compute_ctl: Add OTEL tracing to incoming HTTP requests and startup (#10971)

We lost this with the switch to axum for the HTTP server. Add it back.

In addition to just resurrecting the functionality we had before, pass
the tracing context of the /configure HTTP request to the start_postgres
operation that runs in the main thread. This way, the 'start_postgres'
and all its sub-spans like getting the basebackup become children of the
HTTP request span. This allows end-to-end tracing of a compute start,
all the way from the proxy to the SQL queries executed by compute_ctl as
part of compute startup.

Cargo.lock

@@ -1342,7 +1342,9 @@ dependencies = [
  "tokio-util",
  "tower 0.5.2",
  "tower-http",
+ "tower-otel",
  "tracing",
+ "tracing-opentelemetry",
  "tracing-subscriber",
  "tracing-utils",
  "url",
@@ -4484,18 +4486,18 @@ dependencies = [
 
 [[package]]
 name = "pin-project"
-version = "1.1.0"
+version = "1.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c95a7476719eab1e366eaf73d0260af3021184f18177925b07f54b30089ceead"
+checksum = "dfe2e71e1471fe07709406bf725f710b02927c9c54b2b5b2ec0e8087d97c327d"
 dependencies = [
  "pin-project-internal",
 ]
 
 [[package]]
 name = "pin-project-internal"
-version = "1.1.0"
+version = "1.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "39407670928234ebc5e6e580247dd567ad73a3578460c5990f9503df207e8f07"
+checksum = "f6e859e6e5bd50440ab63c47e3ebabc90f26251f7c73c3d3e837b74a1cc3fa67"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -7294,6 +7296,20 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "121c2a6cda46980bb0fcd1647ffaf6cd3fc79a013de288782836f6df9c48780e"
 
+[[package]]
+name = "tower-otel"
+version = "0.2.0"
+source = "git+https://github.com/mattiapenati/tower-otel?rev=56a7321053bcb72443888257b622ba0d43a11fcd#56a7321053bcb72443888257b622ba0d43a11fcd"
+dependencies = [
+ "http 1.1.0",
+ "opentelemetry",
+ "pin-project",
+ "tower-layer",
+ "tower-service",
+ "tracing",
+ "tracing-opentelemetry",
+]
+
 [[package]]
 name = "tower-service"
 version = "0.3.3"

Cargo.toml

@@ -193,6 +193,10 @@ toml_edit = "0.22"
 tonic = {version = "0.12.3", default-features = false, features = ["channel", "tls", "tls-roots"]}
 tower = { version = "0.5.2", default-features = false }
 tower-http = { version = "0.6.2", features = ["request-id", "trace"] }
+
+# This revision uses opentelemetry 0.27. There's no tag for it.
+tower-otel = { git = "https://github.com/mattiapenati/tower-otel", rev = "56a7321053bcb72443888257b622ba0d43a11fcd" }
+
 tower-service = "0.3.3"
 tracing = "0.1"
 tracing-error = "0.2"

compute_tools/Cargo.toml

@@ -46,7 +46,9 @@ tokio = { workspace = true, features = ["rt", "rt-multi-thread"] }
 tokio-postgres.workspace = true
 tokio-util.workspace = true
 tokio-stream.workspace = true
+tower-otel.workspace = true
 tracing.workspace = true
+tracing-opentelemetry.workspace = true
 tracing-subscriber.workspace = true
 tracing-utils.workspace = true
 thiserror.workspace = true

compute_tools/src/bin/compute_ctl.rs

@@ -406,6 +406,21 @@ fn start_postgres(
 ) -> Result<(Option<PostgresHandle>, StartPostgresResult)> {
     // We got all we need, update the state.
     let mut state = compute.state.lock().unwrap();
+
+    // Create a tracing span for the startup operation.
+    //
+    // We could otherwise just annotate the function with #[instrument], but if
+    // we're being configured from a /configure HTTP request, we want the
+    // startup to be considered part of the /configure request.
+    let _this_entered = {
+        // Temporarily enter the /configure request's span, so that the new span
+        // becomes its child.
+        let _parent_entered = state.startup_span.take().map(|p| p.entered());
+
+        tracing::info_span!("start_postgres")
+    }
+    .entered();
+
     state.set_status(ComputeStatus::Init, &compute.state_changed);
 
     info!(

compute_tools/src/compute.rs

@@ -110,7 +110,23 @@ pub struct ComputeState {
     /// compute wasn't used since start.
     pub last_active: Option<DateTime<Utc>>,
     pub error: Option<String>,
+
+    /// Compute spec. This can be received from the CLI or - more likely -
+    /// passed by the control plane with a /configure HTTP request.
     pub pspec: Option<ParsedSpec>,
+
+    /// If the spec is passed by a /configure request, 'startup_span' is the
+    /// /configure request's tracing span. The main thread enters it when it
+    /// processes the compute startup, so that the compute startup is considered
+    /// to be part of the /configure request for tracing purposes.
+    ///
+    /// If the request handling thread/task called startup_compute() directly,
+    /// it would automatically be a child of the request handling span, and we
+    /// wouldn't need this. But because we use the main thread to perform the
+    /// startup, and the /configure task just waits for it to finish, we need to
+    /// set up the span relationship ourselves.
+    pub startup_span: Option<tracing::span::Span>,
+
     pub metrics: ComputeMetrics,
 }
 
@@ -122,6 +138,7 @@ impl ComputeState {
             last_active: None,
             error: None,
             pspec: None,
+            startup_span: None,
             metrics: ComputeMetrics::default(),
         }
     }

compute_tools/src/http/routes/configure.rs

@@ -45,13 +45,18 @@ pub(in crate::http) async fn configure(
             return JsonResponse::invalid_status(state.status);
         }
 
+        // Pass the tracing span to the main thread that performs the startup,
+        // so that the start_compute operation is considered a child of this
+        // configure request for tracing purposes.
+        state.startup_span = Some(tracing::Span::current());
+
         state.pspec = Some(pspec);
         state.set_status(ComputeStatus::ConfigurationPending, &compute.state_changed);
         drop(state);
     }
 
     // Spawn a blocking thread to wait for compute to become Running. This is
-    // needed to do not block the main pool of workers and be able to serve
+    // needed to not block the main pool of workers and to be able to serve
     // other requests while some particular request is waiting for compute to
     // finish configuration.
     let c = compute.clone();

compute_tools/src/http/server.rs

@@ -121,6 +121,7 @@ impl From<Server> for Router<Arc<ComputeNode>> {
                 )
                 .layer(PropagateRequestIdLayer::x_request_id()),
         )
+            .layer(tower_otel::trace::HttpLayer::server(tracing::Level::INFO))
     }
 }