feat(compute): Add some basic compute_ctl metrics (#10504)

## Problem

There are several parts of `compute_ctl` with a very low visibility of
errors:
1. DB migrations that run async in the background after compute start.
2. Requests made to control plane (currently only `GetSpec`).
3. Requests made to the remote extensions server.

## Summary of changes

Add new counters to quickly evaluate the amount of errors among the
fleet.

Part of neondatabase/cloud#17590

compute_tools/src/extension_server.rs

@@ -85,6 +85,8 @@ use tracing::info;
 use tracing::log::warn;
 use zstd::stream::read::Decoder;
 
+use crate::metrics::{REMOTE_EXT_REQUESTS_FAILED, REMOTE_EXT_REQUESTS_TOTAL, UNKNOWN_HTTP_STATUS};
+
 fn get_pg_config(argument: &str, pgbin: &str) -> String {
     // gives the result of `pg_config [argument]`
     // where argument is a flag like `--version` or `--sharedir`
@@ -258,21 +260,60 @@ async fn download_extension_tar(ext_remote_storage: &str, ext_path: &str) -> Res
 
     info!("Download extension {:?} from uri {:?}", ext_path, uri);
 
-    let resp = reqwest::get(uri).await?;
+    REMOTE_EXT_REQUESTS_TOTAL.with_label_values(&[]).inc();
+
+    match do_extension_server_request(&uri).await {
+        Ok(resp) => {
+            info!(
+                "Successfully downloaded remote extension data {:?}",
+                ext_path
+            );
+            Ok(resp)
+        }
+        Err((msg, status)) => {
+            let status_str = status
+                .map(|s| s.to_string())
+                .unwrap_or(UNKNOWN_HTTP_STATUS.to_string());
+            REMOTE_EXT_REQUESTS_FAILED
+                .with_label_values(&[&status_str])
+                .inc();
+            bail!(msg);
+        }
+    }
+}
+
+// Do a single remote extensions server request.
+// Return result or (error message + status code) in case of any failures.
+async fn do_extension_server_request(uri: &str) -> Result<Bytes, (String, Option<StatusCode>)> {
+    let resp = reqwest::get(uri).await.map_err(|e| {
+        (
+            format!("could not perform remote extensions server request: {}", e),
+            None,
+        )
+    })?;
+    let status = resp.status();
 
-    match resp.status() {
+    match status {
         StatusCode::OK => match resp.bytes().await {
-            Ok(resp) => {
-                info!("Download extension {:?} completed successfully", ext_path);
-                Ok(resp)
-            }
-            Err(e) => bail!("could not deserialize remote extension response: {}", e),
+            Ok(resp) => Ok(resp),
+            Err(e) => Err((
+                format!("could not read remote extensions server response: {}", e),
+                // It's fine to return and report error with status as 200 OK,
+                // because we still failed to read the response.
+                Some(status),
+            )),
         },
-        StatusCode::SERVICE_UNAVAILABLE => bail!("remote extension is temporarily unavailable"),
-        _ => bail!(
-            "unexpected remote extension response status code: {}",
-            resp.status()
-        ),
+        StatusCode::SERVICE_UNAVAILABLE => Err((
+            "remote extensions server is temporarily unavailable".to_string(),
+            Some(status),
+        )),
+        _ => Err((
+            format!(
+                "unexpected remote extensions server response status code: {}",
+                status
+            ),
+            Some(status),
+        )),
     }
 }
 

compute_tools/src/http/routes/metrics.rs

@@ -2,17 +2,16 @@ use axum::{body::Body, response::Response};
 use http::header::CONTENT_TYPE;
 use http::StatusCode;
 use metrics::proto::MetricFamily;
-use metrics::Encoder;
-use metrics::TextEncoder;
+use metrics::{Encoder, TextEncoder};
 
-use crate::{http::JsonResponse, installed_extensions};
+use crate::{http::JsonResponse, metrics::collect};
 
 /// Expose Prometheus metrics.
 pub(in crate::http) async fn get_metrics() -> Response {
     // When we call TextEncoder::encode() below, it will immediately return an
     // error if a metric family has no metrics, so we need to preemptively
     // filter out metric families with no metrics.
-    let metrics = installed_extensions::collect()
+    let metrics = collect()
         .into_iter()
         .filter(|m| !m.get_metric().is_empty())
         .collect::<Vec<MetricFamily>>();

compute_tools/src/installed_extensions.rs

@@ -1,13 +1,10 @@
 use compute_api::responses::{InstalledExtension, InstalledExtensions};
-use metrics::proto::MetricFamily;
 use std::collections::HashMap;
 
 use anyhow::Result;
 use postgres::{Client, NoTls};
 
-use metrics::core::Collector;
-use metrics::{register_uint_gauge_vec, UIntGaugeVec};
-use once_cell::sync::Lazy;
+use crate::metrics::INSTALLED_EXTENSIONS;
 
 /// We don't reuse get_existing_dbs() just for code clarity
 /// and to make database listing query here more explicit.
@@ -102,16 +99,3 @@ pub fn get_installed_extensions(mut conf: postgres::config::Config) -> Result<In
         extensions: extensions_map.into_values().collect(),
     })
 }
-
-static INSTALLED_EXTENSIONS: Lazy<UIntGaugeVec> = Lazy::new(|| {
-    register_uint_gauge_vec!(
-        "compute_installed_extensions",
-        "Number of databases where the version of extension is installed",
-        &["extension_name", "version", "owned_by_superuser"]
-    )
-    .expect("failed to define a metric")
-});
-
-pub fn collect() -> Vec<MetricFamily> {
-    INSTALLED_EXTENSIONS.collect()
-}

compute_tools/src/lib.rs

@@ -16,6 +16,7 @@ pub mod extension_server;
 pub mod installed_extensions;
 pub mod local_proxy;
 pub mod lsn_lease;
+pub mod metrics;
 mod migration;
 pub mod monitor;
 pub mod params;

compute_tools/src/metrics.rs

@@ -0,0 +1,90 @@
+use metrics::core::Collector;
+use metrics::proto::MetricFamily;
+use metrics::{register_int_counter_vec, register_uint_gauge_vec, IntCounterVec, UIntGaugeVec};
+use once_cell::sync::Lazy;
+
+pub(crate) static INSTALLED_EXTENSIONS: Lazy<UIntGaugeVec> = Lazy::new(|| {
+    register_uint_gauge_vec!(
+        "compute_installed_extensions",
+        "Number of databases where the version of extension is installed",
+        &["extension_name", "version", "owned_by_superuser"]
+    )
+    .expect("failed to define a metric")
+});
+
+// Normally, any HTTP API request is described by METHOD (e.g. GET, POST, etc.) + PATH,
+// but for all our APIs we defined a 'slug'/method/operationId in the OpenAPI spec.
+// And it's fair to call it a 'RPC' (Remote Procedure Call).
+pub enum CPlaneRequestRPC {
+    GetSpec,
+}
+
+impl CPlaneRequestRPC {
+    pub fn as_str(&self) -> &str {
+        match self {
+            CPlaneRequestRPC::GetSpec => "GetSpec",
+        }
+    }
+}
+
+pub const UNKNOWN_HTTP_STATUS: &str = "unknown";
+
+pub(crate) static CPLANE_REQUESTS_TOTAL: Lazy<IntCounterVec> = Lazy::new(|| {
+    register_int_counter_vec!(
+        "compute_ctl_cplane_requests_total",
+        "Total number of control plane requests made by compute_ctl",
+        &["rpc"]
+    )
+    .expect("failed to define a metric")
+});
+
+pub(crate) static CPLANE_REQUESTS_FAILED: Lazy<IntCounterVec> = Lazy::new(|| {
+    register_int_counter_vec!(
+        "compute_ctl_cplane_requests_failed_total",
+        "Total number of failed control plane requests made by compute_ctl",
+        &["rpc", "http_status"]
+    )
+    .expect("failed to define a metric")
+});
+
+/// Total number of failed database migrations. Per-compute, this is actually a boolean metric,
+/// either empty or with a single value (1, migration_id) because we stop at the first failure.
+/// Yet, the sum over the fleet will provide the total number of failures.
+pub(crate) static DB_MIGRATION_FAILED: Lazy<IntCounterVec> = Lazy::new(|| {
+    register_int_counter_vec!(
+        "compute_ctl_db_migration_failed_total",
+        "Total number of failed database migrations",
+        &["migration_id"]
+    )
+    .expect("failed to define a metric")
+});
+
+pub(crate) static REMOTE_EXT_REQUESTS_TOTAL: Lazy<IntCounterVec> = Lazy::new(|| {
+    register_int_counter_vec!(
+        "compute_ctl_remote_ext_requests_total",
+        "Total number of requests made by compute_ctl to download extensions from S3 proxy",
+        // Do not use any labels like extension name yet.
+        // We can add them later if needed.
+        &[]
+    )
+    .expect("failed to define a metric")
+});
+
+pub(crate) static REMOTE_EXT_REQUESTS_FAILED: Lazy<IntCounterVec> = Lazy::new(|| {
+    register_int_counter_vec!(
+        "compute_ctl_remote_ext_requests_failed_total",
+        "Total number of failed requests to S3 proxy",
+        &["http_status"]
+    )
+    .expect("failed to define a metric")
+});
+
+pub fn collect() -> Vec<MetricFamily> {
+    let mut metrics = INSTALLED_EXTENSIONS.collect();
+    metrics.extend(CPLANE_REQUESTS_TOTAL.collect());
+    metrics.extend(CPLANE_REQUESTS_FAILED.collect());
+    metrics.extend(DB_MIGRATION_FAILED.collect());
+    metrics.extend(REMOTE_EXT_REQUESTS_TOTAL.collect());
+    metrics.extend(REMOTE_EXT_REQUESTS_FAILED.collect());
+    metrics
+}

compute_tools/src/migration.rs

@@ -1,7 +1,9 @@
 use anyhow::{Context, Result};
 use fail::fail_point;
 use postgres::{Client, Transaction};
-use tracing::info;
+use tracing::{error, info};
+
+use crate::metrics::DB_MIGRATION_FAILED;
 
 /// Runs a series of migrations on a target database
 pub(crate) struct MigrationRunner<'m> {
@@ -78,24 +80,31 @@ impl<'m> MigrationRunner<'m> {
         Ok(())
     }
 
-    /// Run an individual migration
-    fn run_migration(txn: &mut Transaction, migration_id: i64, migration: &str) -> Result<()> {
+    /// Run an individual migration in a separate transaction block.
+    fn run_migration(client: &mut Client, migration_id: i64, migration: &str) -> Result<()> {
+        let mut txn = client
+            .transaction()
+            .with_context(|| format!("begin transaction for migration {migration_id}"))?;
+
         if migration.starts_with("-- SKIP") {
             info!("Skipping migration id={}", migration_id);
 
             // Even though we are skipping the migration, updating the
             // migration ID should help keep logic easy to understand when
             // trying to understand the state of a cluster.
-            Self::update_migration_id(txn, migration_id)?;
+            Self::update_migration_id(&mut txn, migration_id)?;
         } else {
             info!("Running migration id={}:\n{}\n", migration_id, migration);
 
             txn.simple_query(migration)
                 .with_context(|| format!("apply migration {migration_id}"))?;
 
-            Self::update_migration_id(txn, migration_id)?;
+            Self::update_migration_id(&mut txn, migration_id)?;
         }
 
+        txn.commit()
+            .with_context(|| format!("commit transaction for migration {migration_id}"))?;
+
         Ok(())
     }
 
@@ -109,19 +118,20 @@ impl<'m> MigrationRunner<'m> {
             // The index lags the migration ID by 1, so the current migration
             // ID is also the next index
             let migration_id = (current_migration + 1) as i64;
-
-            let mut txn = self
-                .client
-                .transaction()
-                .with_context(|| format!("begin transaction for migration {migration_id}"))?;
-
-            Self::run_migration(&mut txn, migration_id, self.migrations[current_migration])
-                .with_context(|| format!("running migration {migration_id}"))?;
-
-            txn.commit()
-                .with_context(|| format!("commit transaction for migration {migration_id}"))?;
-
-            info!("Finished migration id={}", migration_id);
+            let migration = self.migrations[current_migration];
+
+            match Self::run_migration(self.client, migration_id, migration) {
+                Ok(_) => {
+                    info!("Finished migration id={}", migration_id);
+                }
+                Err(e) => {
+                    error!("Failed to run migration id={}: {}", migration_id, e);
+                    DB_MIGRATION_FAILED
+                        .with_label_values(&[migration_id.to_string().as_str()])
+                        .inc();
+                    return Err(e);
+                }
+            }
 
             current_migration += 1;
         }