Add metric for tracking S3 endpoint calls by RPC method

src/access.rs

@@ -0,0 +1,20 @@
+use s3s::S3Result;
+use s3s::access::{S3Access, S3AccessContext};
+
+use crate::telemetry;
+
+pub(crate) struct TelemetryAccess;
+
+#[async_trait::async_trait]
+impl S3Access for TelemetryAccess {
+    async fn check(&self, cx: &mut S3AccessContext<'_>) -> S3Result<()> {
+        // to use this check to record telemetry data is an abuse of the S3Access trait, but we use it here to have a single location where we can record the requested operations
+        telemetry::record_endpoint_call(cx.s3_op().name());
+
+        if cx.credentials().is_none() {
+            return Err(s3s::s3_error!(AccessDenied, "Signature is required"));
+        }
+
+        Ok(())
+    }
+}

src/lib.rs

@@ -36,6 +36,7 @@ pub use self::proxy::{S3CachingProxy, range_to_string};
 pub use self::s3_cache::{CacheKey, CachedObject, S3Cache};
 pub use self::statistics::UniqueRequestedObjectsStatisticsTracker;
 
+mod access;
 mod auth;
 mod config;
 mod error;
@@ -148,6 +149,7 @@ where
     let service = {
         let mut b = S3ServiceBuilder::new(caching_proxy);
         b.set_auth(auth::create_auth(&config));
+        b.set_access(access::TelemetryAccess);
         let upstream_health_endpoint = Url::parse(&config.upstream_endpoint)
             .unwrap()
             .join("/minio/health/ready")

src/telemetry.rs

@@ -5,7 +5,7 @@ use opentelemetry::KeyValue;
 use opentelemetry::metrics::{Counter, Gauge, Histogram};
 use opentelemetry_appender_tracing::layer::OpenTelemetryTracingBridge;
 use opentelemetry_otlp::{Compression, WithExportConfig, WithTonicConfig};
-use prometheus::{HistogramOpts, IntCounter, IntGauge, Registry};
+use prometheus::{HistogramOpts, IntCounter, IntCounterVec, IntGauge, Opts, Registry};
 use tracing::{error, info};
 use tracing_subscriber::{EnvFilter, layer::SubscriberExt, util::SubscriberInitExt};
 
@@ -681,6 +681,35 @@ pub(crate) fn record_request_duration(data: RequestDuration) {
     REQUEST_DURATION_MS.record(milliseconds, &attributes);
 }
 
+// MARK: - Endpoint Calls
+
+pub(crate) fn record_endpoint_call(method: &str) {
+    static ENDPOINT_TOTAL: LazyLock<Counter<u64>> = LazyLock::new(|| {
+        opentelemetry::global::meter(CARGO_CRATE_NAME)
+            .u64_counter("s3_cache.endpoint_call_total")
+            .with_description("Number of S3 endpoint method calls")
+            .build()
+    });
+
+    static PROM_ENDPOINT_TOTAL: LazyLock<IntCounterVec> = LazyLock::new(|| {
+        let counter = IntCounterVec::new(
+            Opts::new(
+                "s3_cache_endpoint_call_total",
+                "Number of S3 endpoint method calls",
+            ),
+            &["rpc_method"],
+        )
+        .unwrap();
+        PROMETHEUS_REGISTRY
+            .register(Box::new(counter.clone()))
+            .unwrap();
+        counter
+    });
+
+    PROM_ENDPOINT_TOTAL.with_label_values(&[method]).inc();
+    ENDPOINT_TOTAL.add(1, &[KeyValue::new("rpc.method", method.to_owned())]);
+}
+
 // MARK: Response Body Sizes
 
 /// Attributes based on: https://opentelemetry.io/docs/specs/semconv/http/http-metrics/#http-server