initial prometheus metrics (#1536)

* service-new: cosmetic changes

* overseer: draft of prometheus metrics

* metrics: update active_leaves metrics

* metrics: extract into functions

* metrics: resolve XXX

* metrics: it's ugly, but it works

* Bump Substrate

* metrics: move a bunch of code around

* Bumb substrate again

* metrics: fix a warning

* fix a warning in runtime

* metrics: statements signed

* metrics: statements impl RegisterMetrics

* metrics: refactor Metrics trait

* metrics: add Metrics assoc type to JobTrait

* metrics: move Metrics trait to util

* metrics: fix overseer

* metrics: fix backing

* metrics: fix candidate validation

* metrics: derive Default

* metrics: docs

* metrics: add stubs for other subsystems

* metrics: add more stubs and fix compilation

* metrics: fix doctest

* metrics: move to subsystem

* metrics: fix candidate validation

* metrics: bitfield signing

* metrics: av store

* metrics: chain API

* metrics: runtime API

* metrics: stub for avad

* metrics: candidates seconded

* metrics: ok I gave up

* metrics: provisioner

* metrics: remove a clone by requiring Metrics: Sync

* metrics: YAGNI

* metrics: remove another TODO

* metrics: for later

* metrics: add parachain_ prefix

* metrics: s/signed_statement/signed_statements

* utils: add a comment for job metrics

* metrics: address review comments

* metrics: oops

* metrics: make sure to save files before commit 😅

* use _total suffix for requests metrics

Co-authored-by: Max Inden <mail@max-inden.de>

* metrics: add tests for overseer

* update Cargo.lock

* overseer: add a test for CollationGeneration

* collation-generation: impl metrics

* collation-generation: use kebab-case for name

* collation-generation: add a constructor

Co-authored-by: Gav Wood <gavin@parity.io>
Co-authored-by: Ashley Ruglys <ashley.ruglys@gmail.com>
Co-authored-by: Max Inden <mail@max-inden.de>

polkadot/Cargo.lock

@@ -4861,6 +4861,7 @@ dependencies = [
  "sc-network",
  "smallvec 1.4.1",
  "sp-core",
+ "substrate-prometheus-endpoint",
 ]
 
 [[package]]

polkadot/node/collation-generation/src/lib.rs

@@ -31,6 +31,7 @@ use polkadot_node_subsystem::{
 	errors::RuntimeApiError,
 	messages::{AllMessages, CollationGenerationMessage, CollatorProtocolMessage},
 	FromOverseer, SpawnedSubsystem, Subsystem, SubsystemContext, SubsystemError, SubsystemResult,
+	metrics::{self, prometheus},
 };
 use polkadot_node_subsystem_util::{
 	self as util, request_availability_cores_ctx, request_global_validation_data_ctx,
@@ -47,9 +48,18 @@ use std::sync::Arc;
 /// Collation Generation Subsystem
 pub struct CollationGenerationSubsystem {
 	config: Option<Arc<CollationGenerationConfig>>,
+	metrics: Metrics,
 }
 
 impl CollationGenerationSubsystem {
+	/// Create a new instance of the `CollationGenerationSubsystem`.
+	pub fn new(metrics: Metrics) -> Self {
+		Self {
+			config: None,
+			metrics,
+		}
+	}
+
 	/// Run this subsystem
 	///
 	/// Conceptually, this is very simple: it just loops forever.
@@ -112,8 +122,9 @@ impl CollationGenerationSubsystem {
 			Ok(Signal(ActiveLeaves(ActiveLeavesUpdate { activated, .. }))) => {
 				// follow the procedure from the guide
 				if let Some(config) = &self.config {
+					let metrics = self.metrics.clone();
 					if let Err(err) =
-						handle_new_activations(config.clone(), &activated, ctx, sender).await
+						handle_new_activations(config.clone(), &activated, ctx, metrics, sender).await
 					{
 						log::warn!(target: "collation_generation", "failed to handle new activations: {:?}", err);
 						return true;
@@ -146,13 +157,13 @@ impl<Context> Subsystem<Context> for CollationGenerationSubsystem
 where
 	Context: SubsystemContext<Message = CollationGenerationMessage>,
 {
-	fn start(self, ctx: Context) -> SpawnedSubsystem {
-		let subsystem = CollationGenerationSubsystem { config: None };
+	type Metrics = Metrics;
 
-		let future = Box::pin(subsystem.run(ctx));
+	fn start(self, ctx: Context) -> SpawnedSubsystem {
+		let future = Box::pin(self.run(ctx));
 
 		SpawnedSubsystem {
-			name: "CollationGenerationSubsystem",
+			name: "collation-generation-subsystem",
 			future,
 		}
 	}
@@ -178,6 +189,7 @@ async fn handle_new_activations<Context: SubsystemContext>(
 	config: Arc<CollationGenerationConfig>,
 	activated: &[Hash],
 	ctx: &mut Context,
+	metrics: Metrics,
 	sender: &mpsc::Sender<AllMessages>,
 ) -> Result<()> {
 	// follow the procedure from the guide:
@@ -230,6 +242,7 @@ async fn handle_new_activations<Context: SubsystemContext>(
 			let task_global_validation_data = global_validation_data.clone();
 			let task_config = config.clone();
 			let mut task_sender = sender.clone();
+			let metrics = metrics.clone();
 			ctx.spawn("collation generation collation builder", Box::pin(async move {
 				let validation_data_hash =
 					validation_data_hash(&task_global_validation_data, &local_validation_data);
@@ -273,6 +286,8 @@ async fn handle_new_activations<Context: SubsystemContext>(
 					},
 				};
 
+				metrics.on_collation_generated();
+
 				if let Err(err) = task_sender.send(AllMessages::CollatorProtocol(
 					CollatorProtocolMessage::DistributeCollation(ccr, collation.proof_of_validity)
 				)).await {
@@ -305,6 +320,38 @@ fn erasure_root(
 	Ok(polkadot_erasure_coding::branches(&chunks).root())
 }
 
+#[derive(Clone)]
+struct MetricsInner {
+	collations_generated_total: prometheus::Counter<prometheus::U64>,
+}
+
+/// CollationGenerationSubsystem metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_collation_generated(&self) {
+		if let Some(metrics) = &self.0 {
+			metrics.collations_generated_total.inc();
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> std::result::Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			collations_generated_total: prometheus::register(
+				prometheus::Counter::new(
+					"parachain_collations_generated_total",
+					"Number of collations generated."
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	mod handle_new_activations {
@@ -411,6 +458,7 @@ mod tests {
 					test_config(123),
 					&subsystem_activated_hashes,
 					&mut ctx,
+					Metrics(None),
 					&tx,
 				)
 				.await
@@ -498,7 +546,7 @@ mod tests {
 			let (tx, _rx) = mpsc::channel(0);
 
 			subsystem_test_harness(overseer, |mut ctx| async move {
-				handle_new_activations(test_config(16), &activated_hashes, &mut ctx, &tx)
+				handle_new_activations(test_config(16), &activated_hashes, &mut ctx, Metrics(None), &tx)
 					.await
 					.unwrap();
 			});
@@ -581,7 +629,7 @@ mod tests {
 			let sent_messages = Arc::new(Mutex::new(Vec::new()));
 			let subsystem_sent_messages = sent_messages.clone();
 			subsystem_test_harness(overseer, |mut ctx| async move {
-				handle_new_activations(subsystem_config, &activated_hashes, &mut ctx, &tx)
+				handle_new_activations(subsystem_config, &activated_hashes, &mut ctx, Metrics(None), &tx)
 					.await
 					.unwrap();
 

polkadot/node/core/av-store/src/lib.rs

@@ -34,6 +34,7 @@ use polkadot_primitives::v1::{
 };
 use polkadot_subsystem::{
 	FromOverseer, SubsystemError, Subsystem, SubsystemContext, SpawnedSubsystem,
+	metrics::{self, prometheus},
 };
 use polkadot_subsystem::messages::AvailabilityStoreMessage;
 
@@ -59,6 +60,7 @@ enum Error {
 /// An implementation of the Availability Store subsystem.
 pub struct AvailabilityStoreSubsystem {
 	inner: Arc<dyn KeyValueDB>,
+	metrics: Metrics,
 }
 
 fn available_data_key(candidate_hash: &Hash) -> Vec<u8> {
@@ -85,7 +87,7 @@ pub struct Config {
 
 impl AvailabilityStoreSubsystem {
 	/// Create a new `AvailabilityStoreSubsystem` with a given config on disk.
-	pub fn new_on_disk(config: Config) -> io::Result<Self> {
+	pub fn new_on_disk(config: Config, metrics: Metrics) -> io::Result<Self> {
 		let mut db_config = DatabaseConfig::with_columns(columns::NUM_COLUMNS);
 
 		if let Some(cache_size) = config.cache_size {
@@ -106,6 +108,7 @@ impl AvailabilityStoreSubsystem {
 
 		Ok(Self {
 			inner: Arc::new(db),
+			metrics,
 		})
 	}
 
@@ -113,6 +116,7 @@ impl AvailabilityStoreSubsystem {
 	fn new_in_memory(inner: Arc<dyn KeyValueDB>) -> Self {
 		Self {
 			inner,
+			metrics: Metrics(None),
 		}
 	}
 }
@@ -130,7 +134,7 @@ where
 					Ok(FromOverseer::Signal(Conclude)) => break,
 					Ok(FromOverseer::Signal(_)) => (),
 					Ok(FromOverseer::Communication { msg }) => {
-						process_message(&subsystem.inner, msg)?;
+						process_message(&subsystem.inner, &subsystem.metrics, msg)?;
 					}
 					Err(_) => break,
 				}
@@ -142,7 +146,7 @@ where
 	Ok(())
 }
 
-fn process_message(db: &Arc<dyn KeyValueDB>, msg: AvailabilityStoreMessage) -> Result<(), Error> {
+fn process_message(db: &Arc<dyn KeyValueDB>, metrics: &Metrics, msg: AvailabilityStoreMessage) -> Result<(), Error> {
 	use AvailabilityStoreMessage::*;
 	match msg {
 		QueryAvailableData(hash, tx) => {
@@ -152,10 +156,10 @@ fn process_message(db: &Arc<dyn KeyValueDB>, msg: AvailabilityStoreMessage) -> R
 			tx.send(available_data(db, &hash).is_some()).map_err(|_| oneshot::Canceled)?;
 		}
 		QueryChunk(hash, id, tx) => {
-			tx.send(get_chunk(db, &hash, id)?).map_err(|_| oneshot::Canceled)?;
+			tx.send(get_chunk(db, &hash, id, metrics)?).map_err(|_| oneshot::Canceled)?;
 		}
 		QueryChunkAvailability(hash, id, tx) => {
-			tx.send(get_chunk(db, &hash, id)?.is_some()).map_err(|_| oneshot::Canceled)?;
+			tx.send(get_chunk(db, &hash, id, metrics)?.is_some()).map_err(|_| oneshot::Canceled)?;
 		}
 		StoreChunk(hash, id, chunk, tx) => {
 			match store_chunk(db, &hash, id, chunk) {
@@ -169,7 +173,7 @@ fn process_message(db: &Arc<dyn KeyValueDB>, msg: AvailabilityStoreMessage) -> R
 			}
 		}
 		StoreAvailableData(hash, id, n_validators, av_data, tx) => {
-			match store_available_data(db, &hash, id, n_validators, av_data) {
+			match store_available_data(db, &hash, id, n_validators, av_data, metrics) {
 				Err(e) => {
 					tx.send(Err(())).map_err(|_| oneshot::Canceled)?;
 					return Err(e);
@@ -194,11 +198,12 @@ fn store_available_data(
 	id: Option<ValidatorIndex>,
 	n_validators: u32,
 	available_data: AvailableData,
+	metrics: &Metrics,
 ) -> Result<(), Error> {
 	let mut tx = DBTransaction::new();
 
 	if let Some(index) = id {
-		let chunks = get_chunks(&available_data, n_validators as usize)?;
+		let chunks = get_chunks(&available_data, n_validators as usize, metrics)?;
 		store_chunk(db, candidate_hash, n_validators, chunks[index as usize].clone())?;
 	}
 
@@ -231,7 +236,7 @@ fn store_chunk(db: &Arc<dyn KeyValueDB>, candidate_hash: &Hash, _n_validators: u
 	Ok(())
 }
 
-fn get_chunk(db: &Arc<dyn KeyValueDB>, candidate_hash: &Hash, index: u32)
+fn get_chunk(db: &Arc<dyn KeyValueDB>, candidate_hash: &Hash, index: u32, metrics: &Metrics)
 	-> Result<Option<ErasureChunk>, Error>
 {
 	if let Some(chunk) = query_inner(
@@ -242,7 +247,7 @@ fn get_chunk(db: &Arc<dyn KeyValueDB>, candidate_hash: &Hash, index: u32)
 	}
 
 	if let Some(data) = available_data(db, candidate_hash) {
-		let mut chunks = get_chunks(&data.data, data.n_validators as usize)?;
+		let mut chunks = get_chunks(&data.data, data.n_validators as usize, metrics)?;
 		let desired_chunk = chunks.get(index as usize).cloned();
 		for chunk in chunks.drain(..) {
 			store_chunk(db, candidate_hash, data.n_validators, chunk)?;
@@ -271,6 +276,8 @@ impl<Context> Subsystem<Context> for AvailabilityStoreSubsystem
 	where
 		Context: SubsystemContext<Message=AvailabilityStoreMessage>,
 {
+	type Metrics = Metrics;
+
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
 		let future = Box::pin(async move {
 			if let Err(e) = run(self, ctx).await {
@@ -285,8 +292,9 @@ impl<Context> Subsystem<Context> for AvailabilityStoreSubsystem
 	}
 }
 
-fn get_chunks(data: &AvailableData, n_validators: usize) -> Result<Vec<ErasureChunk>, Error> {
+fn get_chunks(data: &AvailableData, n_validators: usize, metrics: &Metrics) -> Result<Vec<ErasureChunk>, Error> {
 	let chunks = erasure::obtain_chunks_v1(n_validators, data)?;
+	metrics.on_chunks_received(chunks.len());
 	let branches = erasure::branches(chunks.as_ref());
 
 	Ok(chunks
@@ -302,6 +310,41 @@ fn get_chunks(data: &AvailableData, n_validators: usize) -> Result<Vec<ErasureCh
 	)
 }
 
+#[derive(Clone)]
+struct MetricsInner {
+	received_availability_chunks_total: prometheus::Counter<prometheus::U64>,
+}
+
+/// Availability metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_chunks_received(&self, count: usize) {
+		if let Some(metrics) = &self.0 {
+			use core::convert::TryFrom as _;
+			// assume usize fits into u64
+			let by = u64::try_from(count).unwrap_or_default();
+			metrics.received_availability_chunks_total.inc_by(by);
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			received_availability_chunks_total: prometheus::register(
+				prometheus::Counter::new(
+					"parachain_received_availability_chunks_total",
+					"Number of availability chunks received.",
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
@@ -501,7 +544,8 @@ mod tests {
 				omitted_validation,
 			};
 
-			let chunks_expected = get_chunks(&available_data, n_validators as usize).unwrap();
+			let no_metrics = Metrics(None);
+			let chunks_expected = get_chunks(&available_data, n_validators as usize, &no_metrics).unwrap();
 
 			let (tx, rx) = oneshot::channel();
 			let block_msg = AvailabilityStoreMessage::StoreAvailableData(

polkadot/node/core/backing/src/lib.rs

@@ -45,6 +45,7 @@ use polkadot_subsystem::{
 		ProvisionerMessage, RuntimeApiMessage, StatementDistributionMessage, ValidationFailed,
 		RuntimeApiRequest,
 	},
+	metrics::{self, prometheus},
 };
 use polkadot_node_subsystem_util::{
 	self as util,
@@ -100,6 +101,7 @@ struct CandidateBackingJob {
 	reported_misbehavior_for: HashSet<ValidatorIndex>,
 	table: Table<TableContext>,
 	table_context: TableContext,
+	metrics: Metrics,
 }
 
 const fn group_quorum(n_validators: usize) -> usize {
@@ -432,6 +434,7 @@ impl CandidateBackingJob {
 								&candidate,
 								pov,
 							).await {
+								self.metrics.on_candidate_seconded();
 								self.seconded = Some(candidate_hash);
 							}
 						}
@@ -528,7 +531,9 @@ impl CandidateBackingJob {
 	}
 
 	fn sign_statement(&self, statement: Statement) -> Option<SignedFullStatement> {
-		Some(self.table_context.validator.as_ref()?.sign(statement))
+		let signed = self.table_context.validator.as_ref()?.sign(statement);
+		self.metrics.on_statement_signed();
+		Some(signed)
 	}
 
 	fn check_statement_signature(&self, statement: &SignedFullStatement) -> Result<(), Error> {
@@ -672,12 +677,14 @@ impl util::JobTrait for CandidateBackingJob {
 	type FromJob = FromJob;
 	type Error = Error;
 	type RunArgs = KeyStorePtr;
+	type Metrics = Metrics;
 
 	const NAME: &'static str = "CandidateBackingJob";
 
 	fn run(
 		parent: Hash,
 		keystore: KeyStorePtr,
+		metrics: Metrics,
 		rx_to: mpsc::Receiver<Self::ToJob>,
 		mut tx_from: mpsc::Sender<Self::FromJob>,
 	) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>> {
@@ -764,6 +771,7 @@ impl util::JobTrait for CandidateBackingJob {
 				reported_misbehavior_for: HashSet::new(),
 				table: Table::default(),
 				table_context,
+				metrics,
 			};
 
 			job.run_loop().await
@@ -772,7 +780,53 @@ impl util::JobTrait for CandidateBackingJob {
 	}
 }
 
-delegated_subsystem!(CandidateBackingJob(KeyStorePtr) <- ToJob as CandidateBackingSubsystem);
+#[derive(Clone)]
+struct MetricsInner {
+	signed_statements_total: prometheus::Counter<prometheus::U64>,
+	candidates_seconded_total: prometheus::Counter<prometheus::U64>
+}
+
+/// Candidate backing metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_statement_signed(&self) {
+		if let Some(metrics) = &self.0 {
+			metrics.signed_statements_total.inc();
+		}
+	}
+
+	fn on_candidate_seconded(&self) {
+		if let Some(metrics) = &self.0 {
+			metrics.candidates_seconded_total.inc();
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			signed_statements_total: prometheus::register(
+				prometheus::Counter::new(
+					"parachain_signed_statements_total",
+					"Number of statements signed.",
+				)?,
+				registry,
+			)?,
+			candidates_seconded_total: prometheus::register(
+				prometheus::Counter::new(
+					"parachain_candidates_seconded_total",
+					"Number of candidates seconded.",
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
+delegated_subsystem!(CandidateBackingJob(KeyStorePtr, Metrics) <- ToJob as CandidateBackingSubsystem);
 
 #[cfg(test)]
 mod tests {
@@ -904,7 +958,7 @@ mod tests {
 
 		let (context, virtual_overseer) = polkadot_node_subsystem_test_helpers::make_subsystem_context(pool.clone());
 
-		let subsystem = CandidateBackingSubsystem::run(context, keystore, pool.clone());
+		let subsystem = CandidateBackingSubsystem::run(context, keystore, Metrics(None), pool.clone());
 
 		let test_fut = test(TestHarness {
 			virtual_overseer,

polkadot/node/core/bitfield-signing/src/lib.rs

@@ -29,6 +29,7 @@ use polkadot_node_subsystem::{
 		BitfieldSigningMessage, CandidateBackingMessage, RuntimeApiMessage,
 	},
 	errors::RuntimeApiError,
+	metrics::{self, prometheus},
 };
 use polkadot_node_subsystem_util::{
 	self as util, JobManager, JobTrait, ToJobTrait, Validator
@@ -252,11 +253,44 @@ async fn construct_availability_bitfield(
 	}
 }
 
+#[derive(Clone)]
+struct MetricsInner {
+	bitfields_signed_total: prometheus::Counter<prometheus::U64>,
+}
+
+/// Bitfield signing metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_bitfield_signed(&self) {
+		if let Some(metrics) = &self.0 {
+			metrics.bitfields_signed_total.inc();
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			bitfields_signed_total: prometheus::register(
+				prometheus::Counter::new(
+					"parachain_bitfields_signed_total",
+					"Number of bitfields signed.",
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
 impl JobTrait for BitfieldSigningJob {
 	type ToJob = ToJob;
 	type FromJob = FromJob;
 	type Error = Error;
 	type RunArgs = KeyStorePtr;
+	type Metrics = Metrics;
 
 	const NAME: &'static str = "BitfieldSigningJob";
 
@@ -264,6 +298,7 @@ impl JobTrait for BitfieldSigningJob {
 	fn run(
 		relay_parent: Hash,
 		keystore: Self::RunArgs,
+		metrics: Self::Metrics,
 		_receiver: mpsc::Receiver<ToJob>,
 		mut sender: mpsc::Sender<FromJob>,
 	) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>> {
@@ -295,6 +330,7 @@ impl JobTrait for BitfieldSigningJob {
 			};
 
 			let signed_bitfield = validator.sign(bitfield);
+			metrics.on_bitfield_signed();
 
 			// make an anonymous scope to contain some use statements to simplify creating the outbound message
 			{

polkadot/node/core/candidate-validation/src/lib.rs

@@ -23,9 +23,11 @@
 use polkadot_subsystem::{
 	Subsystem, SubsystemContext, SpawnedSubsystem, SubsystemResult,
 	FromOverseer, OverseerSignal,
-};
-use polkadot_subsystem::messages::{
-	AllMessages, CandidateValidationMessage, RuntimeApiMessage, ValidationFailed, RuntimeApiRequest,
+	messages::{
+		AllMessages, CandidateValidationMessage, RuntimeApiMessage,
+		ValidationFailed, RuntimeApiRequest,
+	},
+	metrics::{self, prometheus},
 };
 use polkadot_subsystem::errors::RuntimeApiError;
 use polkadot_node_primitives::{ValidationResult, ValidationOutputs, InvalidCandidate};
@@ -45,13 +47,63 @@ use futures::prelude::*;
 
 use std::sync::Arc;
 
+const LOG_TARGET: &'static str = "candidate_validation";
+
 /// The candidate validation subsystem.
-pub struct CandidateValidationSubsystem<S>(S);
+pub struct CandidateValidationSubsystem<S> {
+	spawn: S,
+	metrics: Metrics,
+}
+
+#[derive(Clone)]
+struct MetricsInner {
+	validation_requests: prometheus::CounterVec<prometheus::U64>,
+}
+
+/// Candidate validation metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_validation_event(&self, event: &Result<ValidationResult, ValidationFailed>) {
+		if let Some(metrics) = &self.0 {
+			match event {
+				Ok(ValidationResult::Valid(_)) => {
+					metrics.validation_requests.with_label_values(&["valid"]).inc();
+				},
+				Ok(ValidationResult::Invalid(_)) => {
+					metrics.validation_requests.with_label_values(&["invalid"]).inc();
+				},
+				Err(_) => {
+					metrics.validation_requests.with_label_values(&["failed"]).inc();
+				},
+			}
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			validation_requests: prometheus::register(
+				prometheus::CounterVec::new(
+					prometheus::Opts::new(
+						"parachain_validation_requests_total",
+						"Number of validation requests served.",
+					),
+					&["valid", "invalid", "failed"],
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
 
 impl<S> CandidateValidationSubsystem<S> {
 	/// Create a new `CandidateValidationSubsystem` with the given task spawner.
-	pub fn new(spawn: S) -> Self {
-		CandidateValidationSubsystem(spawn)
+	pub fn new(spawn: S, metrics: Metrics) -> Self {
+		CandidateValidationSubsystem { spawn, metrics }
 	}
 }
 
@@ -59,10 +111,12 @@ impl<S, C> Subsystem<C> for CandidateValidationSubsystem<S> where
 	C: SubsystemContext<Message = CandidateValidationMessage>,
 	S: SpawnNamed + Clone + 'static,
 {
+	type Metrics = Metrics;
+
 	fn start(self, ctx: C) -> SpawnedSubsystem {
 		SpawnedSubsystem {
 			name: "candidate-validation-subsystem",
-			future: run(ctx, self.0).map(|_| ()).boxed(),
+			future: run(ctx, self.spawn, self.metrics).map(|_| ()).boxed(),
 		}
 	}
 }
@@ -70,6 +124,7 @@ impl<S, C> Subsystem<C> for CandidateValidationSubsystem<S> where
 async fn run(
 	mut ctx: impl SubsystemContext<Message = CandidateValidationMessage>,
 	spawn: impl SpawnNamed + Clone + 'static,
+	metrics: Metrics,
 )
 	-> SubsystemResult<()>
 {
@@ -95,8 +150,11 @@ async fn run(
 					).await;
 
 					match res {
-						Ok(x) => { let _ = response_sender.send(x); }
-						Err(e)=> return Err(e),
+						Ok(x) => {
+							metrics.on_validation_event(&x);
+							let _ = response_sender.send(x);
+						}
+						Err(e) => return Err(e),
 					}
 				}
 				CandidateValidationMessage::ValidateFromExhaustive(
@@ -117,13 +175,16 @@ async fn run(
 					).await;
 
 					match res {
-						Ok(x) => if let Err(_e) = response_sender.send(x) {
-							log::warn!(
-								target: "candidate_validation",
-								"Requester of candidate validation dropped",
-							)
+						Ok(x) => {
+							metrics.on_validation_event(&x);
+							if let Err(_e) = response_sender.send(x) {
+								log::warn!(
+									target: LOG_TARGET,
+									"Requester of candidate validation dropped",
+								)
+							}
 						},
-						Err(e)=> return Err(e),
+						Err(e) => return Err(e),
 					}
 				}
 			}
@@ -237,7 +298,7 @@ async fn spawn_validate_from_chain_state(
 			Ok(g) => g,
 			Err(e) => {
 				log::warn!(
-					target: "candidate_validation",
+					target: LOG_TARGET,
 					"Error making runtime API request: {:?}",
 					e,
 				);

polkadot/node/core/chain-api/src/lib.rs

@@ -30,6 +30,7 @@ use polkadot_subsystem::{
 	FromOverseer, OverseerSignal,
 	SpawnedSubsystem, Subsystem, SubsystemResult, SubsystemContext,
 	messages::ChainApiMessage,
+	metrics::{self, prometheus},
 };
 use polkadot_primitives::v1::{Block, BlockId};
 use sp_blockchain::HeaderBackend;
@@ -39,13 +40,15 @@ use futures::prelude::*;
 /// The Chain API Subsystem implementation.
 pub struct ChainApiSubsystem<Client> {
 	client: Client,
+	metrics: Metrics,
 }
 
 impl<Client> ChainApiSubsystem<Client> {
 	/// Create a new Chain API subsystem with the given client.
-	pub fn new(client: Client) -> Self {
+	pub fn new(client: Client, metrics: Metrics) -> Self {
 		ChainApiSubsystem {
-			client
+			client,
+			metrics,
 		}
 	}
 }
@@ -54,9 +57,11 @@ impl<Client, Context> Subsystem<Context> for ChainApiSubsystem<Client> where
 	Client: HeaderBackend<Block> + 'static,
 	Context: SubsystemContext<Message = ChainApiMessage>
 {
+	type Metrics = Metrics;
+
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
 		SpawnedSubsystem {
-			future: run(ctx, self.client).map(|_| ()).boxed(),
+			future: run(ctx, self).map(|_| ()).boxed(),
 			name: "chain-api-subsystem",
 		}
 	}
@@ -64,7 +69,7 @@ impl<Client, Context> Subsystem<Context> for ChainApiSubsystem<Client> where
 
 async fn run<Client>(
 	mut ctx: impl SubsystemContext<Message = ChainApiMessage>,
-	client: Client,
+	subsystem: ChainApiSubsystem<Client>,
 ) -> SubsystemResult<()>
 where
 	Client: HeaderBackend<Block>,
@@ -76,23 +81,27 @@ where
 			FromOverseer::Signal(OverseerSignal::BlockFinalized(_)) => {},
 			FromOverseer::Communication { msg } => match msg {
 				ChainApiMessage::BlockNumber(hash, response_channel) => {
-					let result = client.number(hash).map_err(|e| e.to_string().into());
+					let result = subsystem.client.number(hash).map_err(|e| e.to_string().into());
+					subsystem.metrics.on_request(result.is_ok());
 					let _ = response_channel.send(result);
 				},
 				ChainApiMessage::FinalizedBlockHash(number, response_channel) => {
 					// Note: we don't verify it's finalized
-					let result = client.hash(number).map_err(|e| e.to_string().into());
+					let result = subsystem.client.hash(number).map_err(|e| e.to_string().into());
+					subsystem.metrics.on_request(result.is_ok());
 					let _ = response_channel.send(result);
 				},
 				ChainApiMessage::FinalizedBlockNumber(response_channel) => {
-					let result = client.info().finalized_number;
+					let result = subsystem.client.info().finalized_number;
+					// always succeeds
+					subsystem.metrics.on_request(true);
 					let _ = response_channel.send(Ok(result));
 				},
 				ChainApiMessage::Ancestors { hash, k, response_channel } => {
 					let mut hash = hash;
 
 					let next_parent = core::iter::from_fn(|| {
-						let maybe_header = client.header(BlockId::Hash(hash));
+						let maybe_header = subsystem.client.header(BlockId::Hash(hash));
 						match maybe_header {
 							// propagate the error
 							Err(e) => Some(Err(e.to_string().into())),
@@ -106,6 +115,7 @@ where
 					});
 
 					let result = next_parent.take(k).collect::<Result<Vec<_>, _>>();
+					subsystem.metrics.on_request(result.is_ok());
 					let _ = response_channel.send(result);
 				},
 			}
@@ -113,6 +123,46 @@ where
 	}
 }
 
+#[derive(Clone)]
+struct MetricsInner {
+	chain_api_requests: prometheus::CounterVec<prometheus::U64>,
+}
+
+/// Chain API metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_request(&self, succeeded: bool) {
+		if let Some(metrics) = &self.0 {
+			if succeeded {
+				metrics.chain_api_requests.with_label_values(&["succeeded"]).inc();
+			} else {
+				metrics.chain_api_requests.with_label_values(&["failed"]).inc();
+			}
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			chain_api_requests: prometheus::register(
+				prometheus::CounterVec::new(
+					prometheus::Opts::new(
+						"parachain_chain_api_requests_total",
+						"Number of Chain API requests served.",
+					),
+					&["succeeded", "failed"],
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
+
 #[cfg(test)]
 mod tests {
 	use super::*;
@@ -238,7 +288,8 @@ mod tests {
 		let (ctx, ctx_handle) = make_subsystem_context(TaskExecutor::new());
 		let client = TestClient::default();
 
-		let chain_api_task = run(ctx, client.clone()).map(|x| x.unwrap());
+		let subsystem = ChainApiSubsystem::new(client.clone(), Metrics(None));
+		let chain_api_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = test(client, ctx_handle);
 
 		futures::executor::block_on(future::join(chain_api_task, test_task));

polkadot/node/core/provisioner/src/lib.rs

@@ -30,6 +30,7 @@ use polkadot_node_subsystem::{
 		AllMessages, ChainApiMessage, ProvisionableData, ProvisionerInherentData,
 		ProvisionerMessage, RuntimeApiMessage,
 	},
+	metrics::{self, prometheus},
 };
 use polkadot_node_subsystem_util::{
 	self as util,
@@ -50,6 +51,7 @@ struct ProvisioningJob {
 	provisionable_data_channels: Vec<mpsc::Sender<ProvisionableData>>,
 	backed_candidates: Vec<BackedCandidate>,
 	signed_bitfields: Vec<SignedAvailabilityBitfield>,
+	metrics: Metrics,
 }
 
 /// This enum defines the messages that the provisioner is prepared to receive.
@@ -134,6 +136,7 @@ impl JobTrait for ProvisioningJob {
 	type FromJob = FromJob;
 	type Error = Error;
 	type RunArgs = ();
+	type Metrics = Metrics;
 
 	const NAME: &'static str = "ProvisioningJob";
 
@@ -143,11 +146,12 @@ impl JobTrait for ProvisioningJob {
 	fn run(
 		relay_parent: Hash,
 		_run_args: Self::RunArgs,
+		metrics: Self::Metrics,
 		receiver: mpsc::Receiver<ToJob>,
 		sender: mpsc::Sender<FromJob>,
 	) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>> {
 		async move {
-			let job = ProvisioningJob::new(relay_parent, sender, receiver);
+			let job = ProvisioningJob::new(relay_parent, metrics, sender, receiver);
 
 			// it isn't necessary to break run_loop into its own function,
 			// but it's convenient to separate the concerns in this way
@@ -160,6 +164,7 @@ impl JobTrait for ProvisioningJob {
 impl ProvisioningJob {
 	pub fn new(
 		relay_parent: Hash,
+		metrics: Metrics,
 		sender: mpsc::Sender<FromJob>,
 		receiver: mpsc::Receiver<ToJob>,
 	) -> Self {
@@ -170,6 +175,7 @@ impl ProvisioningJob {
 			provisionable_data_channels: Vec::new(),
 			backed_candidates: Vec::new(),
 			signed_bitfields: Vec::new(),
+			metrics,
 		}
 	}
 
@@ -190,7 +196,10 @@ impl ProvisioningJob {
 					)
 					.await
 					{
-						log::warn!(target: "provisioner", "failed to send inherent data: {:?}", err);
+						log::warn!(target: "provisioner", "failed to assemble or send inherent data: {:?}", err);
+						self.metrics.on_inherent_data_request(false);
+					} else {
+						self.metrics.on_inherent_data_request(true);
 					}
 				}
 				ToJob::Provisioner(RequestBlockAuthorshipData(_, sender)) => {
@@ -275,17 +284,9 @@ async fn send_inherent_data(
 	return_sender: oneshot::Sender<ProvisionerInherentData>,
 	mut from_job: mpsc::Sender<FromJob>,
 ) -> Result<(), Error> {
-	let availability_cores = match request_availability_cores(relay_parent, &mut from_job)
+	let availability_cores = request_availability_cores(relay_parent, &mut from_job)
 		.await?
-		.await?
-	{
-		Ok(cores) => cores,
-		Err(runtime_err) => {
-			// Don't take down the node on runtime API errors.
-			log::warn!(target: "provisioner", "Encountered a runtime API error: {:?}", runtime_err);
-			return Ok(());
-		}
-	};
+		.await??;
 
 	let bitfields = select_availability_bitfields(&availability_cores, bitfields);
 	let candidates = select_candidates(
@@ -467,7 +468,47 @@ fn bitfields_indicate_availability(
 	3 * availability.count_ones() >= 2 * availability.len()
 }
 
-delegated_subsystem!(ProvisioningJob(()) <- ToJob as ProvisioningSubsystem);
+#[derive(Clone)]
+struct MetricsInner {
+	inherent_data_requests: prometheus::CounterVec<prometheus::U64>,
+}
+
+/// Candidate backing metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_inherent_data_request(&self, succeeded: bool) {
+		if let Some(metrics) = &self.0 {
+			if succeeded {
+				metrics.inherent_data_requests.with_label_values(&["succeded"]).inc();
+			} else {
+				metrics.inherent_data_requests.with_label_values(&["failed"]).inc();
+			}
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			inherent_data_requests: prometheus::register(
+				prometheus::CounterVec::new(
+					prometheus::Opts::new(
+						"parachain_inherent_data_requests_total",
+						"Number of InherentData requests served by provisioner.",
+					),
+					&["succeeded", "failed"],
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
+
+delegated_subsystem!(ProvisioningJob((), Metrics) <- ToJob as ProvisioningSubsystem);
 
 #[cfg(test)]
 mod tests {

polkadot/node/core/runtime-api/src/lib.rs

@@ -22,6 +22,7 @@
 use polkadot_subsystem::{
 	Subsystem, SpawnedSubsystem, SubsystemResult, SubsystemContext,
 	FromOverseer, OverseerSignal,
+	metrics::{self, prometheus},
 };
 use polkadot_subsystem::messages::{
 	RuntimeApiMessage, RuntimeApiRequest as Request,
@@ -34,12 +35,15 @@ use sp_api::{ProvideRuntimeApi};
 use futures::prelude::*;
 
 /// The `RuntimeApiSubsystem`. See module docs for more details.
-pub struct RuntimeApiSubsystem<Client>(Client);
+pub struct RuntimeApiSubsystem<Client> {
+	client: Client,
+	metrics: Metrics,
+}
 
 impl<Client> RuntimeApiSubsystem<Client> {
-	/// Create a new Runtime API subsystem wrapping the given client.
-	pub fn new(client: Client) -> Self {
-		RuntimeApiSubsystem(client)
+	/// Create a new Runtime API subsystem wrapping the given client and metrics.
+	pub fn new(client: Client, metrics: Metrics) -> Self {
+		RuntimeApiSubsystem { client, metrics }
 	}
 }
 
@@ -48,9 +52,11 @@ impl<Client, Context> Subsystem<Context> for RuntimeApiSubsystem<Client> where
 	Client::Api: ParachainHost<Block>,
 	Context: SubsystemContext<Message = RuntimeApiMessage>
 {
+	type Metrics = Metrics;
+
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
 		SpawnedSubsystem {
-			future: run(ctx, self.0).map(|_| ()).boxed(),
+			future: run(ctx, self).map(|_| ()).boxed(),
 			name: "runtime-api-subsystem",
 		}
 	}
@@ -58,7 +64,7 @@ impl<Client, Context> Subsystem<Context> for RuntimeApiSubsystem<Client> where
 
 async fn run<Client>(
 	mut ctx: impl SubsystemContext<Message = RuntimeApiMessage>,
-	client: Client,
+	subsystem: RuntimeApiSubsystem<Client>,
 ) -> SubsystemResult<()> where
 	Client: ProvideRuntimeApi<Block>,
 	Client::Api: ParachainHost<Block>,
@@ -70,7 +76,8 @@ async fn run<Client>(
 			FromOverseer::Signal(OverseerSignal::BlockFinalized(_)) => {},
 			FromOverseer::Communication { msg } => match msg {
 				RuntimeApiMessage::Request(relay_parent, request) => make_runtime_api_request(
-					&client,
+					&subsystem.client,
+					&subsystem.metrics,
 					relay_parent,
 					request,
 				),
@@ -81,6 +88,7 @@ async fn run<Client>(
 
 fn make_runtime_api_request<Client>(
 	client: &Client,
+	metrics: &Metrics,
 	relay_parent: Hash,
 	request: Request,
 ) where
@@ -93,7 +101,7 @@ fn make_runtime_api_request<Client>(
 			let api = client.runtime_api();
 			let res = api.$api_name(&BlockId::Hash(relay_parent), $($param),*)
 				.map_err(|e| RuntimeApiError::from(format!("{:?}", e)));
-
+			metrics.on_request(res.is_ok());
 			let _ = sender.send(res);
 		}}
 	}
@@ -114,6 +122,45 @@ fn make_runtime_api_request<Client>(
 	}
 }
 
+#[derive(Clone)]
+struct MetricsInner {
+	chain_api_requests: prometheus::CounterVec<prometheus::U64>,
+}
+
+/// Runtime API metrics.
+#[derive(Default, Clone)]
+pub struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_request(&self, succeeded: bool) {
+		if let Some(metrics) = &self.0 {
+			if succeeded {
+				metrics.chain_api_requests.with_label_values(&["succeeded"]).inc();
+			} else {
+				metrics.chain_api_requests.with_label_values(&["failed"]).inc();
+			}
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			chain_api_requests: prometheus::register(
+				prometheus::CounterVec::new(
+					prometheus::Opts::new(
+						"parachain_runtime_api_requests_total",
+						"Number of Runtime API requests served.",
+					),
+					&["succeeded", "failed"],
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
@@ -216,7 +263,8 @@ mod tests {
 		let runtime_api = MockRuntimeApi::default();
 		let relay_parent = [1; 32].into();
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -238,7 +286,8 @@ mod tests {
 		let runtime_api = MockRuntimeApi::default();
 		let relay_parent = [1; 32].into();
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -260,7 +309,8 @@ mod tests {
 		let runtime_api = MockRuntimeApi::default();
 		let relay_parent = [1; 32].into();
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -282,7 +332,8 @@ mod tests {
 		let runtime_api = MockRuntimeApi::default();
 		let relay_parent = [1; 32].into();
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -308,7 +359,8 @@ mod tests {
 
 		runtime_api.local_validation_data.insert(para_a, Default::default());
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -343,7 +395,8 @@ mod tests {
 		let runtime_api = MockRuntimeApi::default();
 		let relay_parent = [1; 32].into();
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -369,7 +422,8 @@ mod tests {
 
 		runtime_api.validation_code.insert(para_a, Default::default());
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -408,7 +462,8 @@ mod tests {
 
 		runtime_api.candidate_pending_availability.insert(para_a, Default::default());
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 
@@ -444,7 +499,8 @@ mod tests {
 		let runtime_api = MockRuntimeApi::default();
 		let relay_parent = [1; 32].into();
 
-		let subsystem_task = run(ctx, runtime_api.clone()).map(|x| x.unwrap());
+		let subsystem = RuntimeApiSubsystem::new(runtime_api.clone(), Metrics(None));
+		let subsystem_task = run(ctx, subsystem).map(|x| x.unwrap());
 		let test_task = async move {
 			let (tx, rx) = oneshot::channel();
 

polkadot/node/network/availability-distribution/src/lib.rs

@@ -756,6 +756,8 @@ impl<Context> Subsystem<Context> for AvailabilityDistributionSubsystem
 where
 	Context: SubsystemContext<Message = AvailabilityDistributionMessage> + Sync + Send,
 {
+	type Metrics = ();
+
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
 		SpawnedSubsystem {
 			name: "availability-distribution-subsystem",

polkadot/node/network/bitfield-distribution/src/lib.rs

@@ -558,6 +558,8 @@ impl<C> Subsystem<C> for BitfieldDistribution
 where
 	C: SubsystemContext<Message = BitfieldDistributionMessage> + Sync + Send,
 {
+	type Metrics = ();
+
 	fn start(self, ctx: C) -> SpawnedSubsystem {
 		SpawnedSubsystem {
 			name: "bitfield-distribution-subsystem",

polkadot/node/network/bridge/src/lib.rs

@@ -205,6 +205,8 @@ impl<Net, Context> Subsystem<Context> for NetworkBridge<Net>
 		Net: Network,
 		Context: SubsystemContext<Message=NetworkBridgeMessage>,
 {
+	type Metrics = ();
+
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
 		// Swallow error because failure is fatal to the node and we log with more precision
 		// within `run_network`.

polkadot/node/network/pov-distribution/src/lib.rs

@@ -51,6 +51,8 @@ pub struct PoVDistribution;
 impl<C> Subsystem<C> for PoVDistribution
 	where C: SubsystemContext<Message = PoVDistributionMessage>
 {
+	type Metrics = ();
+
 	fn start(self, ctx: C) -> SpawnedSubsystem {
 		// Swallow error because failure is fatal to the node and we log with more precision
 		// within `run`.

polkadot/node/network/statement-distribution/src/lib.rs

@@ -65,6 +65,8 @@ pub struct StatementDistribution;
 impl<C> Subsystem<C> for StatementDistribution
 	where C: SubsystemContext<Message=StatementDistributionMessage>
 {
+	type Metrics = ();
+
 	fn start(self, ctx: C) -> SpawnedSubsystem {
 		// Swallow error because failure is fatal to the node and we log with more precision
 		// within `run`.

polkadot/node/overseer/examples/minimal-example.rs

@@ -76,6 +76,8 @@ impl Subsystem1 {
 impl<C> Subsystem<C> for Subsystem1
 	where C: SubsystemContext<Message=CandidateBackingMessage>
 {
+	type Metrics = (); // no Prometheus metrics
+
 	fn start(self, ctx: C) -> SpawnedSubsystem {
 		let future = Box::pin(async move {
 			Self::run(ctx).await;
@@ -121,6 +123,8 @@ impl Subsystem2 {
 impl<C> Subsystem<C> for Subsystem2
 	where C: SubsystemContext<Message=CandidateValidationMessage>
 {
+	type Metrics = (); // no Prometheus metrics
+
 	fn start(self, ctx: C) -> SpawnedSubsystem {
 		let future = Box::pin(async move {
 			Self::run(ctx).await;
@@ -161,6 +165,7 @@ fn main() {
 		let (overseer, _handler) = Overseer::new(
 			vec![],
 			all_subsystems,
+			None,
 			spawner,
 		).unwrap();
 		let overseer_fut = overseer.run().fuse();

polkadot/node/overseer/src/lib.rs

@@ -84,6 +84,7 @@ use polkadot_subsystem::messages::{
 pub use polkadot_subsystem::{
 	Subsystem, SubsystemContext, OverseerSignal, FromOverseer, SubsystemError, SubsystemResult,
 	SpawnedSubsystem, ActiveLeavesUpdate,
+	metrics::{self, prometheus},
 };
 use polkadot_node_primitives::SpawnNamed;
 
@@ -92,6 +93,9 @@ use polkadot_node_primitives::SpawnNamed;
 const CHANNEL_CAPACITY: usize = 1024;
 // A graceful `Overseer` teardown time delay.
 const STOP_DELAY: u64 = 1;
+// Target for logs.
+const LOG_TARGET: &'static str = "overseer";
+
 
 /// A type of messages that are sent from [`Subsystem`] to [`Overseer`].
 ///
@@ -325,10 +329,6 @@ impl<M: Send + 'static> SubsystemContext for OverseerSubsystemContext<M> {
 	}
 }
 
-/// A subsystem compatible with the overseer - one which can be run in the context of the
-/// overseer.
-pub type CompatibleSubsystem<M> = Box<dyn Subsystem<OverseerSubsystemContext<M>> + Send>;
-
 /// A subsystem that we oversee.
 ///
 /// Ties together the [`Subsystem`] itself and it's running instance
@@ -336,7 +336,6 @@ pub type CompatibleSubsystem<M> = Box<dyn Subsystem<OverseerSubsystemContext<M>>
 /// for whatever reason).
 ///
 /// [`Subsystem`]: trait.Subsystem.html
-#[allow(dead_code)]
 struct OverseenSubsystem<M> {
 	instance: Option<SubsystemInstance<M>>,
 }
@@ -407,6 +406,9 @@ pub struct Overseer<S: SpawnNamed> {
 
 	/// The set of the "active leaves".
 	active_leaves: HashSet<(Hash, BlockNumber)>,
+
+	/// Various Prometheus metrics.
+	metrics: Metrics,
 }
 
 /// This struct is passed as an argument to create a new instance of an [`Overseer`].
@@ -453,6 +455,52 @@ pub struct AllSubsystems<CV, CB, CS, SD, AD, BS, BD, P, PoVD, RA, AS, NB, CA, CG
 	pub collator_protocol: CP,
 }
 
+/// Overseer Prometheus metrics.
+#[derive(Clone)]
+struct MetricsInner {
+	activated_heads_total: prometheus::Counter<prometheus::U64>,
+	deactivated_heads_total: prometheus::Counter<prometheus::U64>,
+}
+
+#[derive(Default, Clone)]
+struct Metrics(Option<MetricsInner>);
+
+impl Metrics {
+	fn on_head_activated(&self) {
+		if let Some(metrics) = &self.0 {
+			metrics.activated_heads_total.inc();
+		}
+	}
+
+	fn on_head_deactivated(&self) {
+		if let Some(metrics) = &self.0 {
+			metrics.deactivated_heads_total.inc();
+		}
+	}
+}
+
+impl metrics::Metrics for Metrics {
+	fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError> {
+		let metrics = MetricsInner {
+			activated_heads_total: prometheus::register(
+				prometheus::Counter::new(
+					"parachain_activated_heads_total",
+					"Number of activated heads."
+				)?,
+				registry,
+			)?,
+			deactivated_heads_total: prometheus::register(
+				prometheus::Counter::new(
+					"parachain_deactivated_heads_total",
+					"Number of deactivated heads."
+				)?,
+				registry,
+			)?,
+		};
+		Ok(Metrics(Some(metrics)))
+	}
+}
+
 impl<S> Overseer<S>
 where
 	S: SpawnNamed,
@@ -500,8 +548,10 @@ where
 	/// struct ValidationSubsystem;
 	///
 	/// impl<C> Subsystem<C> for ValidationSubsystem
-	/// 	where C: SubsystemContext<Message=CandidateValidationMessage>
+	///     where C: SubsystemContext<Message=CandidateValidationMessage>
 	/// {
+	///     type Metrics = ();
+	///
 	///     fn start(
 	///         self,
 	///         mut ctx: C,
@@ -539,6 +589,7 @@ where
 	/// let (overseer, _handler) = Overseer::new(
 	///     vec![],
 	///     all_subsystems,
+	///     None,
 	///     spawner,
 	/// ).unwrap();
 	///
@@ -558,6 +609,7 @@ where
 	pub fn new<CV, CB, CS, SD, AD, BS, BD, P, PoVD, RA, AS, NB, CA, CG, CP>(
 		leaves: impl IntoIterator<Item = BlockInfo>,
 		all_subsystems: AllSubsystems<CV, CB, CS, SD, AD, BS, BD, P, PoVD, RA, AS, NB, CA, CG, CP>,
+		prometheus_registry: Option<&prometheus::Registry>,
 		mut s: S,
 	) -> SubsystemResult<(Self, OverseerHandler)>
 	where
@@ -692,13 +744,15 @@ where
 			all_subsystems.collator_protocol,
 		)?;
 
-		let active_leaves = HashSet::new();
-
 		let leaves = leaves
 			.into_iter()
 			.map(|BlockInfo { hash, parent_hash: _, number }| (hash, number))
 			.collect();
 
+		let active_leaves = HashSet::new();
+
+		let metrics = <Metrics as metrics::Metrics>::register(prometheus_registry);
+
 		let this = Self {
 			candidate_validation_subsystem,
 			candidate_backing_subsystem,
@@ -721,6 +775,7 @@ where
 			events_rx,
 			leaves,
 			active_leaves,
+			metrics,
 		};
 
 		Ok((this, handler))
@@ -811,6 +866,7 @@ where
 		for leaf in leaves.into_iter() {
 			update.activated.push(leaf.0);
 			self.active_leaves.insert(leaf);
+			self.metrics.on_head_activated();
 		}
 
 		self.broadcast_signal(OverseerSignal::ActiveLeaves(update)).await?;
@@ -850,7 +906,7 @@ where
 
 			// Some subsystem exited? It's time to panic.
 			if let Poll::Ready(Some(finished)) = poll!(self.running_subsystems.next()) {
-				log::error!("Subsystem finished unexpectedly {:?}", finished);
+				log::error!(target: LOG_TARGET, "Subsystem finished unexpectedly {:?}", finished);
 				self.stop().await;
 				return Err(SubsystemError);
 			}
@@ -865,11 +921,13 @@ where
 
 		if let Some(parent) = block.number.checked_sub(1).and_then(|number| self.active_leaves.take(&(block.parent_hash, number))) {
 			update.deactivated.push(parent.0);
+			self.metrics.on_head_deactivated();
 		}
 
 		if !self.active_leaves.contains(&(block.hash, block.number)) {
 			update.activated.push(block.hash);
 			self.active_leaves.insert((block.hash, block.number));
+			self.metrics.on_head_activated();
 		}
 
 		self.broadcast_signal(OverseerSignal::ActiveLeaves(update)).await?;
@@ -879,10 +937,12 @@ where
 
 	async fn block_finalized(&mut self, block: BlockInfo) -> SubsystemResult<()> {
 		let mut update = ActiveLeavesUpdate::default();
+		let metrics = &self.metrics;
 
 		self.active_leaves.retain(|(h, n)| {
 			if *n <= block.number {
 				update.deactivated.push(*h);
+				metrics.on_head_deactivated();
 				false
 			} else {
 				true
@@ -1103,6 +1163,8 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem1
 		where C: SubsystemContext<Message=CandidateValidationMessage>
 	{
+		type Metrics = ();
+
 		fn start(self, mut ctx: C) -> SpawnedSubsystem {
 			let mut sender = self.0;
 			SpawnedSubsystem {
@@ -1131,6 +1193,8 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem2
 		where C: SubsystemContext<Message=CandidateBackingMessage>
 	{
+		type Metrics = ();
+
 		fn start(self, mut ctx: C) -> SpawnedSubsystem {
 			let sender = self.0.clone();
 			SpawnedSubsystem {
@@ -1177,6 +1241,8 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem4
 		where C: SubsystemContext<Message=CandidateBackingMessage>
 	{
+		type Metrics = ();
+
 		fn start(self, mut _ctx: C) -> SpawnedSubsystem {
 			SpawnedSubsystem {
 				name: "test-subsystem-4",
@@ -1187,6 +1253,7 @@ mod tests {
 		}
 	}
 
+
 	// Checks that a minimal configuration of two jobs can run and exchange messages.
 	#[test]
 	fn overseer_works() {
@@ -1216,6 +1283,7 @@ mod tests {
 			let (overseer, mut handler) = Overseer::new(
 				vec![],
 				all_subsystems,
+				None,
 				spawner,
 			).unwrap();
 			let overseer_fut = overseer.run().fuse();
@@ -1252,6 +1320,86 @@ mod tests {
 			assert_eq!(s1_results, (0..10).collect::<Vec<_>>());
 		});
 	}
+
+	// Checks activated/deactivated metrics are updated properly.
+	#[test]
+	fn overseer_metrics_work() {
+		let spawner = sp_core::testing::TaskExecutor::new();
+
+		executor::block_on(async move {
+			let first_block_hash = [1; 32].into();
+			let second_block_hash = [2; 32].into();
+			let third_block_hash = [3; 32].into();
+
+			let first_block = BlockInfo {
+				hash: first_block_hash,
+				parent_hash: [0; 32].into(),
+				number: 1,
+			};
+			let second_block = BlockInfo {
+				hash: second_block_hash,
+				parent_hash: first_block_hash,
+				number: 2,
+			};
+			let third_block = BlockInfo {
+				hash: third_block_hash,
+				parent_hash: second_block_hash,
+				number: 3,
+			};
+
+			let all_subsystems = AllSubsystems {
+				collation_generation: DummySubsystem,
+				candidate_validation: DummySubsystem,
+				candidate_backing: DummySubsystem,
+				candidate_selection: DummySubsystem,
+				collator_protocol: DummySubsystem,
+				statement_distribution: DummySubsystem,
+				availability_distribution: DummySubsystem,
+				bitfield_signing: DummySubsystem,
+				bitfield_distribution: DummySubsystem,
+				provisioner: DummySubsystem,
+				pov_distribution: DummySubsystem,
+				runtime_api: DummySubsystem,
+				availability_store: DummySubsystem,
+				network_bridge: DummySubsystem,
+				chain_api: DummySubsystem,
+			};
+			let registry = prometheus::Registry::new();
+			let (overseer, mut handler) = Overseer::new(
+				vec![first_block],
+				all_subsystems,
+				Some(&registry),
+				spawner,
+			).unwrap();
+			let overseer_fut = overseer.run().fuse();
+
+			pin_mut!(overseer_fut);
+
+			handler.block_imported(second_block).await.unwrap();
+			handler.block_imported(third_block).await.unwrap();
+			handler.stop().await.unwrap();
+
+			select! {
+				res = overseer_fut => {
+					assert!(res.is_ok());
+					let (activated, deactivated) = extract_metrics(&registry);
+					assert_eq!(activated, 3);
+					assert_eq!(deactivated, 2);
+				},
+				complete => (),
+			}
+		});
+	}
+
+	fn extract_metrics(registry: &prometheus::Registry) -> (u64, u64) {
+		let gather = registry.gather();
+		assert_eq!(gather[0].get_name(), "parachain_activated_heads_total");
+		assert_eq!(gather[1].get_name(), "parachain_deactivated_heads_total");
+		let activated = gather[0].get_metric()[0].get_counter().get_value() as u64;
+		let deactivated = gather[1].get_metric()[0].get_counter().get_value() as u64;
+		(activated, deactivated)
+	}
+
 	// Spawn a subsystem that immediately exits.
 	//
 	// Should immediately conclude the overseer itself with an error.
@@ -1281,6 +1429,7 @@ mod tests {
 			let (overseer, _handle) = Overseer::new(
 				vec![],
 				all_subsystems,
+				None,
 				spawner,
 			).unwrap();
 			let overseer_fut = overseer.run().fuse();
@@ -1298,6 +1447,8 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem5
 		where C: SubsystemContext<Message=CandidateValidationMessage>
 	{
+		type Metrics = ();
+
 		fn start(self, mut ctx: C) -> SpawnedSubsystem {
 			let mut sender = self.0.clone();
 
@@ -1327,6 +1478,8 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem6
 		where C: SubsystemContext<Message=CandidateBackingMessage>
 	{
+		type Metrics = ();
+
 		fn start(self, mut ctx: C) -> SpawnedSubsystem {
 			let mut sender = self.0.clone();
 
@@ -1400,6 +1553,7 @@ mod tests {
 			let (overseer, mut handler) = Overseer::new(
 				vec![first_block],
 				all_subsystems,
+				None,
 				spawner,
 			).unwrap();
 
@@ -1505,6 +1659,7 @@ mod tests {
 			let (overseer, mut handler) = Overseer::new(
 				vec![first_block, second_block],
 				all_subsystems,
+				None,
 				spawner,
 			).unwrap();
 
@@ -1592,6 +1747,8 @@ mod tests {
 			C: SubsystemContext<Message=M>,
 			M: Send,
 	{
+		type Metrics = ();
+
 		fn start(self, mut ctx: C) -> SpawnedSubsystem {
 			SpawnedSubsystem {
 				name: "counter-subsystem",
@@ -1738,6 +1895,7 @@ mod tests {
 			let (overseer, mut handler) = Overseer::new(
 				vec![],
 				all_subsystems,
+				None,
 				spawner,
 			).unwrap();
 			let overseer_fut = overseer.run().fuse();

polkadot/node/service/src/lib.rs

@@ -277,6 +277,7 @@ fn new_partial<RuntimeApi, Executor>(config: &mut Configuration) -> Result<
 
 fn real_overseer<S: SpawnNamed>(
 	leaves: impl IntoIterator<Item = BlockInfo>,
+	prometheus_registry: Option<&Registry>,
 	s: S,
 ) -> Result<(Overseer<S>, OverseerHandler), ServiceError> {
 	let all_subsystems = AllSubsystems {
@@ -296,9 +297,11 @@ fn real_overseer<S: SpawnNamed>(
 		collation_generation: DummySubsystem,
 		collator_protocol: DummySubsystem,
 	};
+
 	Overseer::new(
 		leaves,
 		all_subsystems,
+		prometheus_registry,
 		s,
 	).map_err(|e| ServiceError::Other(format!("Failed to create an Overseer: {:?}", e)))
 }
@@ -399,7 +402,7 @@ fn new_full<RuntimeApi, Executor>(
 		})
 		.collect();
 
-	let (overseer, handler) = real_overseer(leaves, spawner)?;
+	let (overseer, handler) = real_overseer(leaves, prometheus_registry.as_ref(), spawner)?;
 	let handler_clone = handler.clone();
 
 	task_manager.spawn_essential_handle().spawn_blocking("overseer", Box::pin(async move {
@@ -502,7 +505,7 @@ fn new_full<RuntimeApi, Executor>(
 			inherent_data_providers: inherent_data_providers.clone(),
 			telemetry_on_connect: Some(telemetry_connection_sinks.on_connect_stream()),
 			voting_rule,
-			prometheus_registry: prometheus_registry,
+			prometheus_registry,
 			shared_voter_state,
 		};
 
@@ -533,7 +536,7 @@ fn new_light<Runtime, Dispatch>(mut config: Configuration) -> Result<TaskManager
 		RuntimeApiCollection<StateBackend = sc_client_api::StateBackendFor<LightBackend, Block>>,
 		Dispatch: NativeExecutionDispatch + 'static,
 {
-	crate::set_prometheus_registry(&mut config)?;
+	set_prometheus_registry(&mut config)?;
 	use sc_client_api::backend::RemoteBackend;
 
 	let (client, backend, keystore, mut task_manager, on_demand) =

polkadot/node/subsystem-util/src/lib.rs

@@ -24,6 +24,7 @@ use polkadot_node_subsystem::{
 	errors::{ChainApiError, RuntimeApiError},
 	messages::{AllMessages, RuntimeApiMessage, RuntimeApiRequest, RuntimeApiSender},
 	FromOverseer, SpawnedSubsystem, Subsystem, SubsystemContext, SubsystemError, SubsystemResult,
+	metrics,
 };
 use futures::{
 	channel::{mpsc, oneshot},
@@ -63,11 +64,13 @@ pub mod reexports {
 	};
 }
 
+
 /// Duration a job will wait after sending a stop signal before hard-aborting.
 pub const JOB_GRACEFUL_STOP_DURATION: Duration = Duration::from_secs(1);
 /// Capacity of channels to and from individual jobs
 pub const JOB_CHANNEL_CAPACITY: usize = 64;
 
+
 /// Utility errors
 #[derive(Debug, derive_more::From)]
 pub enum Error {
@@ -446,6 +449,12 @@ pub trait JobTrait: Unpin {
 	///
 	/// If no extra information is needed, it is perfectly acceptable to set it to `()`.
 	type RunArgs: 'static + Send;
+	/// Subsystem-specific Prometheus metrics.
+	///
+	/// Jobs spawned by one subsystem should share the same
+	/// instance of metrics (use `.clone()`).
+	/// The `delegate_subsystem!` macro should take care of this.
+	type Metrics: 'static + metrics::Metrics + Send;
 
 	/// Name of the job, i.e. `CandidateBackingJob`
 	const NAME: &'static str;
@@ -454,6 +463,7 @@ pub trait JobTrait: Unpin {
 	fn run(
 		parent: Hash,
 		run_args: Self::RunArgs,
+		metrics: Self::Metrics,
 		receiver: mpsc::Receiver<Self::ToJob>,
 		sender: mpsc::Sender<Self::FromJob>,
 	) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>>;
@@ -532,7 +542,7 @@ impl<Spawner: SpawnNamed, Job: 'static + JobTrait> Jobs<Spawner, Job> {
 	}
 
 	/// Spawn a new job for this `parent_hash`, with whatever args are appropriate.
-	fn spawn_job(&mut self, parent_hash: Hash, run_args: Job::RunArgs) -> Result<(), Error> {
+	fn spawn_job(&mut self, parent_hash: Hash, run_args: Job::RunArgs, metrics: Job::Metrics) -> Result<(), Error> {
 		let (to_job_tx, to_job_rx) = mpsc::channel(JOB_CHANNEL_CAPACITY);
 		let (from_job_tx, from_job_rx) = mpsc::channel(JOB_CHANNEL_CAPACITY);
 		let (finished_tx, finished) = oneshot::channel();
@@ -541,7 +551,7 @@ impl<Spawner: SpawnNamed, Job: 'static + JobTrait> Jobs<Spawner, Job> {
 		let err_tx = self.errors.clone();
 
 		let (future, abort_handle) = future::abortable(async move {
-			if let Err(e) = Job::run(parent_hash, run_args, to_job_rx, from_job_tx).await {
+			if let Err(e) = Job::run(parent_hash, run_args, metrics, to_job_rx, from_job_tx).await {
 				log::error!(
 					"{}({}) finished with an error {:?}",
 					Job::NAME,
@@ -648,6 +658,7 @@ where
 pub struct JobManager<Spawner, Context, Job: JobTrait> {
 	spawner: Spawner,
 	run_args: Job::RunArgs,
+	metrics: Job::Metrics,
 	context: std::marker::PhantomData<Context>,
 	job: std::marker::PhantomData<Job>,
 	errors: Option<mpsc::Sender<(Option<Hash>, JobsError<Job::Error>)>>,
@@ -662,10 +673,11 @@ where
 	Job::ToJob: TryFrom<AllMessages> + TryFrom<<Context as SubsystemContext>::Message> + Sync,
 {
 	/// Creates a new `Subsystem`.
-	pub fn new(spawner: Spawner, run_args: Job::RunArgs) -> Self {
+	pub fn new(spawner: Spawner, run_args: Job::RunArgs, metrics: Job::Metrics) -> Self {
 		Self {
 			spawner,
 			run_args,
+			metrics,
 			context: std::marker::PhantomData,
 			job: std::marker::PhantomData,
 			errors: None,
@@ -703,6 +715,7 @@ where
 	pub async fn run(
 		mut ctx: Context,
 		run_args: Job::RunArgs,
+		metrics: Job::Metrics,
 		spawner: Spawner,
 		mut err_tx: Option<mpsc::Sender<(Option<Hash>, JobsError<Job::Error>)>>,
 	) {
@@ -714,7 +727,7 @@ where
 
 		loop {
 			select! {
-				incoming = ctx.recv().fuse() => if Self::handle_incoming(incoming, &mut jobs, &run_args, &mut err_tx).await { break },
+				incoming = ctx.recv().fuse() => if Self::handle_incoming(incoming, &mut jobs, &run_args, &metrics, &mut err_tx).await { break },
 				outgoing = jobs.next().fuse() => if Self::handle_outgoing(outgoing, &mut ctx, &mut err_tx).await { break },
 				complete => break,
 			}
@@ -741,6 +754,7 @@ where
 		incoming: SubsystemResult<FromOverseer<Context::Message>>,
 		jobs: &mut Jobs<Spawner, Job>,
 		run_args: &Job::RunArgs,
+		metrics: &Job::Metrics,
 		err_tx: &mut Option<mpsc::Sender<(Option<Hash>, JobsError<Job::Error>)>>,
 	) -> bool {
 		use polkadot_node_subsystem::ActiveLeavesUpdate;
@@ -753,7 +767,8 @@ where
 				deactivated,
 			}))) => {
 				for hash in activated {
-					if let Err(e) = jobs.spawn_job(hash, run_args.clone()) {
+					let metrics = metrics.clone();
+					if let Err(e) = jobs.spawn_job(hash, run_args.clone(), metrics) {
 						log::error!("Failed to spawn a job: {:?}", e);
 						Self::fwd_err(Some(hash), e.into(), err_tx).await;
 						return true;
@@ -849,14 +864,18 @@ where
 	Job: 'static + JobTrait + Send,
 	Job::RunArgs: Clone + Sync,
 	Job::ToJob: TryFrom<AllMessages> + Sync,
+	Job::Metrics: Sync,
 {
+	type Metrics = Job::Metrics;
+
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
 		let spawner = self.spawner.clone();
 		let run_args = self.run_args.clone();
+		let metrics = self.metrics.clone();
 		let errors = self.errors;
 
 		let future = Box::pin(async move {
-			Self::run(ctx, run_args, spawner, errors).await;
+			Self::run(ctx, run_args, metrics, spawner, errors).await;
 		});
 
 		SpawnedSubsystem {
@@ -901,11 +920,11 @@ where
 /// ```
 #[macro_export]
 macro_rules! delegated_subsystem {
-	($job:ident($run_args:ty) <- $to_job:ty as $subsystem:ident) => {
-		delegated_subsystem!($job($run_args) <- $to_job as $subsystem; stringify!($subsystem));
+	($job:ident($run_args:ty, $metrics:ty) <- $to_job:ty as $subsystem:ident) => {
+		delegated_subsystem!($job($run_args, $metrics) <- $to_job as $subsystem; stringify!($subsystem));
 	};
 
-	($job:ident($run_args:ty) <- $to_job:ty as $subsystem:ident; $subsystem_name:expr) => {
+	($job:ident($run_args:ty, $metrics:ty) <- $to_job:ty as $subsystem:ident; $subsystem_name:expr) => {
 		#[doc = "Manager type for the "]
 		#[doc = $subsystem_name]
 		type Manager<Spawner, Context> = $crate::JobManager<Spawner, Context, $job>;
@@ -924,15 +943,15 @@ macro_rules! delegated_subsystem {
 		{
 			#[doc = "Creates a new "]
 			#[doc = $subsystem_name]
-			pub fn new(spawner: Spawner, run_args: $run_args) -> Self {
+			pub fn new(spawner: Spawner, run_args: $run_args, metrics: $metrics) -> Self {
 				$subsystem {
-					manager: $crate::JobManager::new(spawner, run_args)
+					manager: $crate::JobManager::new(spawner, run_args, metrics)
 				}
 			}
 
 			/// Run this subsystem
-			pub async fn run(ctx: Context, run_args: $run_args, spawner: Spawner) {
-				<Manager<Spawner, Context>>::run(ctx, run_args, spawner, None).await
+			pub async fn run(ctx: Context, run_args: $run_args, metrics: $metrics, spawner: Spawner) {
+				<Manager<Spawner, Context>>::run(ctx, run_args, metrics, spawner, None).await
 			}
 		}
 
@@ -942,6 +961,8 @@ macro_rules! delegated_subsystem {
 			Context: $crate::reexports::SubsystemContext,
 			<Context as $crate::reexports::SubsystemContext>::Message: Into<$to_job>,
 		{
+			type Metrics = $metrics;
+
 			fn start(self, ctx: Context) -> $crate::reexports::SpawnedSubsystem {
 				self.manager.start(ctx)
 			}
@@ -1061,6 +1082,7 @@ mod tests {
 		// RunArgs get cloned so that each job gets its own owned copy. If you need that, wrap it in
 		// an Arc. Within a testing context, that efficiency is less important.
 		type RunArgs = HashMap<Hash, Vec<FromJob>>;
+		type Metrics = ();
 
 		const NAME: &'static str = "FakeCandidateSelectionJob";
 
@@ -1070,6 +1092,7 @@ mod tests {
 		fn run(
 			parent: Hash,
 			mut run_args: Self::RunArgs,
+			_metrics: Self::Metrics,
 			receiver: mpsc::Receiver<ToJob>,
 			mut sender: mpsc::Sender<FromJob>,
 		) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>> {
@@ -1121,7 +1144,7 @@ mod tests {
 		let (context, overseer_handle) = make_subsystem_context(pool.clone());
 		let (err_tx, err_rx) = mpsc::channel(16);
 
-		let subsystem = FakeCandidateSelectionSubsystem::run(context, run_args, pool, Some(err_tx));
+		let subsystem = FakeCandidateSelectionSubsystem::run(context, run_args, (), pool, Some(err_tx));
 		let test_future = test(overseer_handle, err_rx);
 		let timeout = Delay::new(Duration::from_secs(2));
 
@@ -1196,7 +1219,7 @@ mod tests {
 		let (context, _) = make_subsystem_context::<CandidateSelectionMessage, _>(pool.clone());
 
 		let SpawnedSubsystem { name, .. } =
-			FakeCandidateSelectionSubsystem::new(pool, HashMap::new()).start(context);
+			FakeCandidateSelectionSubsystem::new(pool, HashMap::new(), ()).start(context);
 		assert_eq!(name, "FakeCandidateSelection");
 	}
 }

polkadot/node/subsystem/Cargo.toml

@@ -21,6 +21,7 @@ polkadot-statement-table = { path = "../../statement-table" }
 sc-network = { git = "https://github.com/paritytech/substrate", branch = "master" }
 smallvec = "1.4.1"
 sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }
+substrate-prometheus-endpoint = { git = "https://github.com/paritytech/substrate", branch = "master" }
 
 [dev-dependencies]
 assert_matches = "1.3.0"

polkadot/node/subsystem/src/lib.rs

@@ -19,6 +19,8 @@
 //! Node-side logic for Polkadot is mostly comprised of Subsystems, which are discrete components
 //! that communicate via message-passing. They are coordinated by an overseer, provided by a
 //! separate crate.
+//!
+//! This crate also reexports Prometheus metric types which are expected to be implemented by subsystems.
 
 #![warn(missing_docs)]
 
@@ -128,9 +130,9 @@ impl From<oneshot::Canceled> for SubsystemError {
 }
 
 impl From<futures::task::SpawnError> for SubsystemError {
-    fn from(_: futures::task::SpawnError) -> Self {
+	fn from(_: futures::task::SpawnError) -> Self {
 		Self
-    }
+	}
 }
 
 impl From<std::convert::Infallible> for SubsystemError {
@@ -202,6 +204,9 @@ pub trait SubsystemContext: Send + 'static {
 /// [`Overseer`]: struct.Overseer.html
 /// [`Subsystem`]: trait.Subsystem.html
 pub trait Subsystem<C: SubsystemContext> {
+	/// Subsystem-specific Prometheus metrics.
+	type Metrics: metrics::Metrics;
+
 	/// Start this `Subsystem` and return `SpawnedSubsystem`.
 	fn start(self, ctx: C) -> SpawnedSubsystem;
 }
@@ -211,6 +216,8 @@ pub trait Subsystem<C: SubsystemContext> {
 pub struct DummySubsystem;
 
 impl<C: SubsystemContext> Subsystem<C> for DummySubsystem {
+	type Metrics = ();
+
 	fn start(self, mut ctx: C) -> SpawnedSubsystem {
 		let future = Box::pin(async move {
 			loop {
@@ -227,4 +234,41 @@ impl<C: SubsystemContext> Subsystem<C> for DummySubsystem {
 			future,
 		}
 	}
-}
+}
+
+/// This module reexports Prometheus types and defines the [`Metrics`] trait.
+pub mod metrics {
+	/// Reexport Prometheus types.
+	pub use substrate_prometheus_endpoint as prometheus;
+
+	/// Subsystem- or job-specific Prometheus metrics.
+	///
+	/// Usually implemented as a wrapper for `Option<ActualMetrics>`
+	/// to ensure `Default` bounds or as a dummy type ().
+	/// Prometheus metrics internally hold an `Arc` reference, so cloning them is fine.
+	pub trait Metrics: Default + Clone {
+		/// Try to register metrics in the Prometheus registry.
+		fn try_register(registry: &prometheus::Registry) -> Result<Self, prometheus::PrometheusError>;
+
+		/// Convience method to register metrics in the optional Prometheus registry.
+		/// If the registration fails, prints a warning and returns `Default::default()`.
+		fn register(registry: Option<&prometheus::Registry>) -> Self {
+			registry.map(|r| {
+				match Self::try_register(r) {
+					Err(e) => {
+						log::warn!("Failed to register metrics: {:?}", e);
+						Default::default()
+					},
+					Ok(metrics) => metrics,
+				}
+			}).unwrap_or_default()
+		}
+	}
+
+	// dummy impl
+	impl Metrics for () {
+		fn try_register(_registry: &prometheus::Registry) -> Result<(), prometheus::PrometheusError> {
+			Ok(())
+		}
+	}
+}