prom: Add option to enable a "bazel_remote" HTTP metrics prefix

This makes it possible to differentiate bazel-remote from other
applications that are using the same metrics.

README.md

@@ -432,6 +432,10 @@ OPTIONS:
       endpoint. (default: false, ie disable metrics)
       [$BAZEL_REMOTE_ENABLE_ENDPOINT_METRICS]
 
+   --http_metrics_prefix Prefix HTTP metrics names with `bazel_remote`
+      (default: false, ie no prefix)
+	  [$BAZEL_REMOTE_HTTP_METRICS_PREFIX]
+
    --experimental_remote_asset_api Whether to enable the experimental remote
       asset API implementation. (default: false, ie disable remote asset API)
       [$BAZEL_REMOTE_EXPERIMENTAL_REMOTE_ASSET_API]

config/config.go

@@ -118,6 +118,7 @@ type Config struct {
 	EnableACKeyInstanceMangling bool                      `yaml:"enable_ac_key_instance_mangling"`
 	EnableEndpointMetrics       bool                      `yaml:"enable_endpoint_metrics"`
 	MetricsDurationBuckets      []float64                 `yaml:"endpoint_metrics_duration_buckets"`
+	HttpMetricsPrefix           bool                      `yaml:"http_metrics_prefix"`
 	ExperimentalRemoteAssetAPI  bool                      `yaml:"experimental_remote_asset_api"`
 	HTTPReadTimeout             time.Duration             `yaml:"http_read_timeout"`
 	HTTPWriteTimeout            time.Duration             `yaml:"http_write_timeout"`
@@ -175,6 +176,7 @@ func newFromArgs(dir string, maxSize int, storageMode string, zstdImplementation
 	disableGRPCACDepsCheck bool,
 	enableACKeyInstanceMangling bool,
 	enableEndpointMetrics bool,
+	httpMetricsPrefix bool,
 	experimentalRemoteAssetAPI bool,
 	httpReadTimeout time.Duration,
 	httpWriteTimeout time.Duration,
@@ -211,6 +213,7 @@ func newFromArgs(dir string, maxSize int, storageMode string, zstdImplementation
 		EnableACKeyInstanceMangling: enableACKeyInstanceMangling,
 		EnableEndpointMetrics:       enableEndpointMetrics,
 		MetricsDurationBuckets:      defaultDurationBuckets,
+		HttpMetricsPrefix:           httpMetricsPrefix,
 		ExperimentalRemoteAssetAPI:  experimentalRemoteAssetAPI,
 		HTTPReadTimeout:             httpReadTimeout,
 		HTTPWriteTimeout:            httpWriteTimeout,
@@ -662,6 +665,7 @@ func get(ctx *cli.Context) (*Config, error) {
 		ctx.Bool("disable_grpc_ac_deps_check"),
 		ctx.Bool("enable_ac_key_instance_mangling"),
 		ctx.Bool("enable_endpoint_metrics"),
+		ctx.Bool("http_metrics_prefix"),
 		ctx.Bool("experimental_remote_asset_api"),
 		ctx.Duration("http_read_timeout"),
 		ctx.Duration("http_write_timeout"),

main.go

@@ -287,8 +287,14 @@ func startHttpServer(c *config.Config, httpServer **http.Server,
 	if c.EnableEndpointMetrics {
 		log.Println("Endpoint metrics: enabled")
 
+		prefix := ""
+		if c.HttpMetricsPrefix {
+			prefix = "bazel_remote"
+		}
+
 		metricsMdlw := middleware.New(middleware.Config{
 			Recorder: httpmetrics.NewRecorder(httpmetrics.Config{
+				Prefix:          prefix,
 				DurationBuckets: c.MetricsDurationBuckets,
 			}),
 		})

utils/flags/flags.go

@@ -471,6 +471,12 @@ func GetCliFlags() []cli.Flag {
 			DefaultText: "false, ie disable metrics",
 			EnvVars:     []string{"BAZEL_REMOTE_ENABLE_ENDPOINT_METRICS"},
 		},
+		&cli.BoolFlag{
+			Name:        "http_metrics_prefix",
+			Usage:       "Whether to prefix http metrics with `bazel_remote` or not",
+			DefaultText: "false, ie no prefix",
+			EnvVars:     []string{"BAZEL_REMOTE_HTTP_METRICS_PREFIX"},
+		},
 		&cli.BoolFlag{
 			Name:        "experimental_remote_asset_api",
 			Usage:       "Whether to enable the experimental remote asset API implementation.",