diff --git a/backend/common/src/channel/metered_unbounded.rs b/backend/common/src/channel/metered_unbounded.rs
new file mode 100644
index 0000000..f76e440
--- /dev/null
+++ b/backend/common/src/channel/metered_unbounded.rs
@@ -0,0 +1,191 @@
+use futures::channel::mpsc::{ SendError, TrySendError, UnboundedSender, UnboundedReceiver, unbounded };
+use futures::{ Sink, Stream, SinkExt, StreamExt };
+use std::sync::atomic::{ AtomicUsize, Ordering };
+use std::sync::Arc;
+use std::task::Poll;
+
+/// Create an unbounded channel where we record the current length of the message queue.
+pub fn metered_unbounded<T>() -> (MeteredUnboundedSender<T>, MeteredUnboundedReceiver<T>) {
+    let (tx, rx) = unbounded();
+    let len = Arc::new(AtomicUsize::new(0));
+    let len2 = Arc::clone(&len);
+
+    let tx = MeteredUnboundedSender {
+        inner: tx,
+        len: len
+    };
+    let rx = MeteredUnboundedReceiver {
+        inner: rx,
+        len: len2
+    };
+
+    (tx, rx)
+}
+
+/// This is similar to an `UnboundedSender`, except that we keep track
+/// of the length of the internal message buffer.
+#[derive(Debug, Clone)]
+pub struct MeteredUnboundedSender<T> {
+    inner: UnboundedSender<T>,
+    len: Arc<AtomicUsize>,
+}
+
+impl <T> MeteredUnboundedSender<T> {
+    /// The current number of messages in the queue.
+    pub fn len(&self) -> usize {
+        self.len.load(Ordering::Relaxed)
+    }
+
+    /// Send a message.
+    pub fn unbounded_send(&self, item: T) -> Result<(), TrySendError<T>> {
+        self.len.fetch_add(1, Ordering::Relaxed);
+        self.inner.unbounded_send(item)
+    }
+}
+
+impl <T> Sink<T> for MeteredUnboundedSender<T> {
+    type Error = SendError;
+
+    fn poll_ready(self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.inner.poll_ready(cx)
+    }
+
+    fn start_send(self: std::pin::Pin<&mut Self>, item: T) -> Result<(), Self::Error> {
+        self.unbounded_send(item).map_err(|e| e.into_send_error())
+    }
+
+    fn poll_flush(mut self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.inner.poll_flush_unpin(cx)
+    }
+
+    fn poll_close(mut self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.inner.poll_close_unpin(cx)
+    }
+}
+
+impl <T> Stream for MeteredUnboundedReceiver<T> {
+    type Item = T;
+
+    fn poll_next(mut self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> std::task::Poll<Option<Self::Item>> {
+        let res = self.inner.poll_next_unpin(cx);
+        if matches!(res, Poll::Ready(Some(..))) {
+            self.len.fetch_sub(1, Ordering::Relaxed);
+        }
+        res
+    }
+}
+
+/// This is similar to an `UnboundedReceiver`, except that we keep track
+/// of the length of the internal message buffer.
+#[derive(Debug)]
+pub struct MeteredUnboundedReceiver<T> {
+    inner: UnboundedReceiver<T>,
+    len: Arc<AtomicUsize>,
+}
+
+impl <T> MeteredUnboundedReceiver<T> {
+    /// The current number of messages in the queue.
+    pub fn len(&self) -> usize {
+        self.len.load(Ordering::Relaxed)
+    }
+}
+
+#[cfg(test)]
+mod test {
+
+    use super::*;
+
+    #[tokio::test]
+    async fn channel_len_consistent_with_msgs() {
+        let (tx, mut rx) = metered_unbounded();
+
+        assert_eq!(tx.len(), 0);
+        tx.unbounded_send(1).unwrap();
+        assert_eq!(tx.len(), 1);
+        tx.unbounded_send(2).unwrap();
+        assert_eq!(tx.len(), 2);
+        tx.unbounded_send(3).unwrap();
+        assert_eq!(tx.len(), 3);
+
+        rx.next().await.unwrap();
+        assert_eq!(tx.len(), 2);
+        rx.next().await.unwrap();
+        assert_eq!(tx.len(), 1);
+        rx.next().await.unwrap();
+        assert_eq!(tx.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn channel_len_consistent_with_msgs_sink() {
+        let (mut tx, mut rx) = metered_unbounded::<usize>();
+
+        assert_eq!(tx.len(), 0);
+        tx.send(1).await.unwrap();
+        assert_eq!(tx.len(), 1);
+        tx.send(2).await.unwrap();
+        assert_eq!(tx.len(), 2);
+        tx.send(3).await.unwrap();
+        assert_eq!(tx.len(), 3);
+
+        rx.next().await.unwrap();
+        assert_eq!(tx.len(), 2);
+        rx.next().await.unwrap();
+        assert_eq!(tx.len(), 1);
+        rx.next().await.unwrap();
+        assert_eq!(tx.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn channel_len_consistent_when_send_parallelised() {
+        let (mut tx, mut rx) = metered_unbounded::<usize>();
+
+        // Send lots of messages on a bunch of real threads:
+        let mut join_handles = vec![];
+        for _ in 0..50 {
+            let tx = tx.clone();
+            let join_handle = std::thread::spawn(move || {
+                for i in 0..10000 {
+                    tx.unbounded_send(i).unwrap();
+                }
+            });
+            join_handles.push(join_handle);
+        }
+
+        // When they are done, our len should be accurate:
+        for handle in join_handles {
+            handle.join().unwrap();
+        }
+        assert_eq!(tx.len(), 50 * 10_000);
+
+    }
+
+    #[tokio::test]
+    async fn channel_len_consistent_when_send_and_recv_parallelised() {
+        let (mut tx, mut rx) = metered_unbounded::<usize>();
+
+        // Send lots of messages on a bunch of real threads:
+        let mut join_handles = vec![];
+        for _ in 0..50 {
+            let tx = tx.clone();
+            let join_handle = std::thread::spawn(move || {
+                for i in 0..10000 {
+                    tx.unbounded_send(i).unwrap();
+                }
+            });
+            join_handles.push(join_handle);
+        }
+
+        // While this is happenening, we are trying to receive that same number of msgs:
+        for _ in 0..500_000 {
+            rx.next().await.unwrap();
+        }
+
+        // When they are done, our len should be accurate:
+        for handle in join_handles {
+            handle.join().unwrap();
+        }
+        assert_eq!(tx.len(), 0);
+
+    }
+
+}
\ No newline at end of file
diff --git a/backend/common/src/channel/mod.rs b/backend/common/src/channel/mod.rs
new file mode 100644
index 0000000..dd4b412
--- /dev/null
+++ b/backend/common/src/channel/mod.rs
@@ -0,0 +1,3 @@
+mod metered_unbounded;
+
+pub use metered_unbounded::*;
\ No newline at end of file
diff --git a/backend/common/src/lib.rs b/backend/common/src/lib.rs
index 85e14fa..b863e45 100644
--- a/backend/common/src/lib.rs
+++ b/backend/common/src/lib.rs
@@ -24,6 +24,7 @@ pub mod ready_chunks_all;
 pub mod rolling_total;
 pub mod time;
 pub mod ws_client;
+pub mod channel;
 
 mod assign_id;
 mod dense_map;
diff --git a/backend/telemetry_core/src/aggregator/aggregator.rs b/backend/telemetry_core/src/aggregator/aggregator.rs
index 7c975ee..172a405 100644
--- a/backend/telemetry_core/src/aggregator/aggregator.rs
+++ b/backend/telemetry_core/src/aggregator/aggregator.rs
@@ -74,16 +74,16 @@ impl Aggregator {
         })))
     }
 
-    // This is spawned into a separate task and handles any messages coming
-    // in to the aggregator. If nobody is tolding the tx side of the channel
-    // any more, this task will gracefully end.
+    /// This is spawned into a separate task and handles any messages coming
+    /// in to the aggregator. If nobody is tolding the tx side of the channel
+    /// any more, this task will gracefully end.
     async fn handle_messages(
         rx_from_external: mpsc::UnboundedReceiver<inner_loop::ToAggregator>,
         tx_to_aggregator: mpsc::UnboundedSender<(NodeId, Ipv4Addr)>,
         denylist: Vec<String>,
     ) {
-        inner_loop::InnerLoop::new(rx_from_external, tx_to_aggregator, denylist)
-            .handle()
+        inner_loop::InnerLoop::new(tx_to_aggregator, denylist)
+            .handle(rx_from_external)
             .await;
     }
 
diff --git a/backend/telemetry_core/src/aggregator/inner_loop.rs b/backend/telemetry_core/src/aggregator/inner_loop.rs
index 6cfec73..1b6e0fe 100644
--- a/backend/telemetry_core/src/aggregator/inner_loop.rs
+++ b/backend/telemetry_core/src/aggregator/inner_loop.rs
@@ -23,6 +23,7 @@ use common::{
     internal_messages::{self, MuteReason, ShardNodeId},
     node_message,
     node_types::BlockHash,
+    channel::metered_unbounded,
     time,
 };
 use futures::channel::mpsc;
@@ -127,9 +128,6 @@ pub enum ToFeedWebsocket {
 /// Instances of this are responsible for handling incoming and
 /// outgoing messages in the main aggregator loop.
 pub struct InnerLoop {
-    /// Messages from the outside world come into this:
-    rx_from_external: mpsc::UnboundedReceiver<ToAggregator>,
-
     /// The state of our chains and nodes lives here:
     node_state: State,
     /// We maintain a mapping between NodeId and ConnId+LocalId, so that we know
@@ -158,12 +156,10 @@ pub struct InnerLoop {
 impl InnerLoop {
     /// Create a new inner loop handler with the various state it needs.
     pub fn new(
-        rx_from_external: mpsc::UnboundedReceiver<ToAggregator>,
         tx_to_locator: mpsc::UnboundedSender<(NodeId, Ipv4Addr)>,
         denylist: Vec<String>,
     ) -> Self {
         InnerLoop {
-            rx_from_external,
             node_state: State::new(denylist),
             node_ids: BiMap::new(),
             feed_channels: HashMap::new(),
@@ -178,19 +174,40 @@ impl InnerLoop {
     /// Start handling and responding to incoming messages. Owing to unbounded channels, we actually
     /// only have a single `.await` (in this function). This helps to make it clear that the aggregator loop
     /// will be able to make progress quickly without any potential yield points.
-    pub async fn handle(mut self) {
-        while let Some(msg) = self.rx_from_external.next().await {
-            match msg {
-                ToAggregator::FromFeedWebsocket(feed_conn_id, msg) => {
-                    self.handle_from_feed(feed_conn_id, msg)
-                }
-                ToAggregator::FromShardWebsocket(shard_conn_id, msg) => {
-                    self.handle_from_shard(shard_conn_id, msg)
-                }
-                ToAggregator::FromFindLocation(node_id, location) => {
-                    self.handle_from_find_location(node_id, location)
+    pub async fn handle(mut self, mut rx_from_external: mpsc::UnboundedReceiver<ToAggregator>) {
+
+        let (metered_tx, mut metered_rx) = metered_unbounded();
+
+        tokio::spawn(async move {
+            while let Some(msg) = metered_rx.next().await {
+                match msg {
+                    ToAggregator::FromFeedWebsocket(feed_conn_id, msg) => {
+                        self.handle_from_feed(feed_conn_id, msg)
+                    }
+                    ToAggregator::FromShardWebsocket(shard_conn_id, msg) => {
+                        self.handle_from_shard(shard_conn_id, msg)
+                    }
+                    ToAggregator::FromFindLocation(node_id, location) => {
+                        self.handle_from_find_location(node_id, location)
+                    }
                 }
             }
+        });
+
+        // TEMP: let's monitor message queue len out of interest
+        let tx_len = metered_tx.clone();
+        tokio::spawn(async move {
+            loop {
+                println!("Queue len: {}", tx_len.len());
+                tokio::time::sleep(tokio::time::Duration::from_secs(1)).await
+            }
+        });
+
+        while let Some(msg) = rx_from_external.next().await {
+            if let Err(e) = metered_tx.unbounded_send(msg) {
+                log::error!("Cannot send message into aggregator: {}", e);
+                break;
+            }
         }
     }