entrypoint: add liveness probe endpoint to the sidecar

This change uses the liveness probes as a way to guarantee a regular
period of uninterrupted CPU for the sidecar to complete its prometheus
scrapes and flushes to GMP.

Change-Id: Ic6f0ed38ade237d6179dea12268cd2575d221146

entrypoint.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"net/http"
 	"os"
 	"os/signal"
 	"path/filepath"
@@ -34,6 +35,9 @@ var userConfigFile = "/etc/rungmp/config.yaml"
 var otelConfigFile = "/run/rungmp/otel.yaml"
 var configRefreshInterval = 20 * time.Second
 var selfMetricsPort = 0
+var livenessProbePort = 13133
+var livenessProbePath = "/liveness"
+var delayLivenessProbe = 5 * time.Second
 
 func getRawUserConfig(userConfigFile string) (string, error) {
 	_, err := os.Stat(userConfigFile)
@@ -84,6 +88,16 @@ func generateOtelConfig(ctx context.Context, userConfigFile string) error {
 	return nil
 }
 
+// The container is allocated CPU for the duration of the healthcheck. Delaying
+// the response to this probe allows the container to complete telemetry flushes
+// that may have been throttled.
+//
+// TODO(b/342463831): Use a more reliable way of checking if telemetry is being
+// flushed instead of using a static sleep.
+func healthcheckHandler(w http.ResponseWriter, r *http.Request) {
+	time.Sleep(delayLivenessProbe)
+}
+
 func main() {
 	// SIGINT handles Ctrl+C locally.
 	// SIGTERM handles Cloud Run termination signal.
@@ -101,6 +115,13 @@ func main() {
 		log.Fatal(err)
 	}
 
+	entrypointMux := http.NewServeMux()
+	entrypointMux.HandleFunc(livenessProbePath, healthcheckHandler)
+
+	go func() {
+		http.ListenAndServe(fmt.Sprintf(":%d", livenessProbePort), entrypointMux)
+	}()
+
 	// Spin up new-subprocess that runs the OTel collector and store the PID.
 	// This OTel collector should use the generated config.
 	var procAttr os.ProcAttr

run-service-simple.yaml

@@ -23,21 +23,22 @@ spec:
     metadata:
       annotations:
         run.googleapis.com/execution-environment: gen2
-        run.googleapis.com/cpu-throttling: 'false'
+        run.googleapis.com/cpu-throttling: "false"
         run.googleapis.com/container-dependencies: '{"collector":["app"]}'
     spec:
       containers:
-      - image: "%SAMPLE_APP_IMAGE%"
-        name: app
-        startupProbe:
-          httpGet:
-            path: /startup
-            port: 8000
-        livenessProbe:
-          httpGet:
-            path: /liveness
-            port: 8000
-        ports:
-        - containerPort: 8000
-      - image: us-docker.pkg.dev/cloud-ops-agents-artifacts/cloud-run-gmp-sidecar/cloud-run-gmp-sidecar:1.1.1
-        name: collector
+        - image: "%SAMPLE_APP_IMAGE%"
+          name: app
+          startupProbe:
+            httpGet:
+              path: /startup
+              port: 8000
+          livenessProbe:
+            httpGet:
+              path: /liveness
+              port: 8000
+          ports:
+            - containerPort: 8000
+        - image: us-docker.pkg.dev/cloud-ops-agents-artifacts/cloud-run-gmp-sidecar/cloud-run-gmp-sidecar:1.1.1
+          name: collector
+          # TODO(b/342463134): Post release 1.2.0, update the collector container to use the healthcheck endpoint

run-service.yaml

@@ -23,32 +23,37 @@ spec:
     metadata:
       annotations:
         run.googleapis.com/execution-environment: gen2
-        run.googleapis.com/cpu-throttling: 'false'
         run.googleapis.com/container-dependencies: '{"collector":["app"]}'
-        run.googleapis.com/secrets: '%SECRET%:projects/%PROJECT%/secrets/%SECRET%'
+        run.googleapis.com/secrets: "%SECRET%:projects/%PROJECT%/secrets/%SECRET%"
     spec:
       containers:
-      - image: "%SAMPLE_APP_IMAGE%"
-        name: app
-        startupProbe:
-          httpGet:
-            path: /startup
-            port: 8000
-        livenessProbe:
-          httpGet:
-            path: /liveness
-            port: 8000
-        ports:
-        - containerPort: 8000
-      - image: "%OTELCOL_IMAGE%"
-        name: collector
-        volumeMounts:
-        - mountPath: /etc/rungmp/
-          name: config
+        - image: "%SAMPLE_APP_IMAGE%"
+          name: app
+          startupProbe:
+            httpGet:
+              path: /startup
+              port: 8000
+          livenessProbe:
+            httpGet:
+              path: /liveness
+              port: 8000
+          ports:
+            - containerPort: 8000
+        - image: "%OTELCOL_IMAGE%"
+          name: collector
+          livenessProbe:
+            httpGet:
+              path: /liveness
+              port: 13133
+            timeoutSeconds: 30
+            periodSeconds: 30
+          volumeMounts:
+            - mountPath: /etc/rungmp/
+              name: config
       volumes:
-      - name: config
-        secret:
-          items:
-          - key: latest
-            path: config.yaml
-          secretName: '%SECRET%'
+        - name: config
+          secret:
+            items:
+              - key: latest
+                path: config.yaml
+            secretName: "%SECRET%"