Allow tests to hook up to running process to help with profiling

backend/test_utils/src/workspace/start_server.rs

@@ -11,23 +11,40 @@ use crate::server::{self, Server, Command};
 /// - `TELEMETRY_SHARD_BIN` - path to telemetry_shard binary
 /// - `TELEMETRY_CORE_BIN` - path to telemetry_core binary
 ///
-/// Whatever is not provided will be substituted with a `cargo run` variant instead.
+/// (Whatever is not provided will be substituted with a `cargo run` variant instead)
+///
+/// Or alternately alternately, we can connect to a running instance by providing:
+///
+/// - `TELEMETRY_SUBMIT_HOSTS` - hosts (comma separated) to connect to for telemetry `/submit`s.
+/// - `TELEMETRY_FEED_HOST` - host to connect to for feeds (eg 127.0.0.1:3000)
+///
 pub async fn start_server(release_mode: bool) -> Server {
-
+    // Start to a single process:
     if let Ok(bin) = std::env::var("TELEMETRY_BIN") {
         return Server::start(server::StartOpts::SingleProcess {
             command: Command::new(bin)
         }).await.unwrap();
     }
 
+    // Connect to a running instance:
+    if let Ok(feed_host) = std::env::var("TELEMETRY_FEED_HOST") {
+        let feed_host = feed_host.trim().into();
+        let submit_hosts: Vec<_> = std::env::var("TELEMETRY_SUBMIT_HOSTS")
+            .map(|var| var.split(",").map(|var| var.trim().into()).collect())
+            .unwrap_or(Vec::new());
+        return Server::start(server::StartOpts::ConnectToExisting {
+            feed_host,
+            submit_hosts,
+        }).await.unwrap();
+    }
+
+    // Start a shard and core process:
     let shard_command = std::env::var("TELEMETRY_SHARD_BIN")
         .map(|val| Command::new(val))
         .unwrap_or_else(|_| commands::cargo_run_telemetry_shard(release_mode).expect("must be in rust workspace to run shard command"));
-
     let core_command = std::env::var("TELEMETRY_CORE_BIN")
         .map(|val| Command::new(val))
         .unwrap_or_else(|_| commands::cargo_run_telemetry_core(release_mode).expect("must be in rust workspace to run core command"));
-
     Server::start(server::StartOpts::ShardAndCore {
         shard_command,
         core_command