[feature] Metrics (#503)

* Add basic metrics

* Updated Docs

* Remove http errors

docs/_docs/dev-guide/tavern.md

@@ -14,6 +14,15 @@ If you would like to help contribute to Tavern, please take a look at our [open
 
 ## Configuration
 
+### Metrics
+
+By default, Tavern does not export metrics. You may use the below environment configuration variables to enable [Prometheus](https://prometheus.io/docs/introduction/overview/) metric collection. These metrics become available at the "/metrics" endpoint configured. These metrics are hosted on a separate HTTP server such that it can be restricted to localhost (default). This is because the endpoint is unauthenticated, and would leak sensitive information if it was accessible.
+
+| Env Var | Description | Default | Required |
+| ------- | ----------- | ------- | -------- |
+| ENABLE_METRICS | Set to any value to enable the "/metrics" endpoint. | Disabled | No |
+| HTTP_METRICS_LISTEN_ADDR | Listen address for the metrics HTTP server, it must be different than the value of `HTTP_LISTEN_ADDR`. | `127.0.0.1:8080` | No |
+
 ### MySQL
 
 By default, Tavern operates an in-memory SQLite database. To persist data, a MySQL backend is supported. In order to configure Tavern to use MySQL, the `MYSQL_ADDR` environment variable must be set to the `host[:port]` of the database (e.g. `127.0.0.1`, `mydb.com`, or `mydb.com:3306`). You can reference the [mysql.Config](https://pkg.go.dev/github.com/go-sql-driver/mysql#Config) for additional information about Tavern's MySQL configuration.

go.mod

@@ -17,7 +17,7 @@ require (
 	github.com/vektah/gqlparser/v2 v2.5.10
 	golang.org/x/crypto v0.14.0
 	golang.org/x/net v0.17.0
-	golang.org/x/oauth2 v0.11.0
+	golang.org/x/oauth2 v0.12.0
 	golang.org/x/sync v0.4.0
 	google.golang.org/grpc v1.59.0
 	google.golang.org/protobuf v1.32.0
@@ -31,6 +31,8 @@ require (
 	github.com/agext/levenshtein v1.2.3 // indirect
 	github.com/agnivade/levenshtein v1.1.1 // indirect
 	github.com/apparentlymart/go-textseg/v15 v15.0.0 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.2.0 // indirect
 	github.com/cpuguy83/go-md2man/v2 v2.0.2 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-openapi/inflect v0.19.0 // indirect
@@ -39,17 +41,22 @@ require (
 	github.com/hashicorp/errwrap v1.1.0 // indirect
 	github.com/hashicorp/golang-lru/v2 v2.0.3 // indirect
 	github.com/hashicorp/hcl/v2 v2.18.1 // indirect
+	github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0 // indirect
 	github.com/mitchellh/go-wordwrap v1.0.1 // indirect
 	github.com/mitchellh/mapstructure v1.5.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/prometheus/client_golang v1.18.0 // indirect
+	github.com/prometheus/client_model v0.5.0 // indirect
+	github.com/prometheus/common v0.45.0 // indirect
+	github.com/prometheus/procfs v0.12.0 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/sosodev/duration v1.2.0 // indirect
 	github.com/vmihailenco/msgpack/v5 v5.4.0 // indirect
 	github.com/vmihailenco/tagparser/v2 v2.0.0 // indirect
 	github.com/zclconf/go-cty v1.14.1 // indirect
 	golang.org/x/exp v0.0.0-20231006140011-7918f672742d // indirect
 	golang.org/x/mod v0.13.0 // indirect
-	golang.org/x/sys v0.13.0 // indirect
+	golang.org/x/sys v0.15.0 // indirect
 	golang.org/x/text v0.13.0 // indirect
 	golang.org/x/tools v0.14.0 // indirect
 	google.golang.org/appengine v1.6.7 // indirect

go.sum

@@ -21,6 +21,10 @@ github.com/apparentlymart/go-textseg/v15 v15.0.0 h1:uYvfpb3DyLSCGWnctWKGj857c6ew
 github.com/apparentlymart/go-textseg/v15 v15.0.0/go.mod h1:K8XmNZdhEBkdlyDdvbmmsvpAG721bKi0joRfFdHIWJ4=
 github.com/arbovm/levenshtein v0.0.0-20160628152529-48b4e1c0c4d0 h1:jfIu9sQUG6Ig+0+Ap1h4unLjW6YQJpKZVmUzxsD4E/Q=
 github.com/arbovm/levenshtein v0.0.0-20160628152529-48b4e1c0c4d0/go.mod h1:t2tdKJDJF9BV14lnkjHmOQgcvEKgtqs5a1N3LNdJhGE=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
+github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/cpuguy83/go-md2man/v2 v2.0.0-20190314233015-f79a8a8ca69d/go.mod h1:maD7wRr/U5Z6m/iR4s+kqSMx2CaBsrgA7czyZG/E6dU=
 github.com/cpuguy83/go-md2man/v2 v2.0.2 h1:p1EgwI/C7NhT0JmVkwCD2ZBK8j4aeHQX2pMHHBfMQ6w=
 github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
@@ -57,16 +61,27 @@ github.com/hashicorp/golang-lru/v2 v2.0.3/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyf
 github.com/hashicorp/hcl/v2 v2.18.1 h1:6nxnOJFku1EuSawSD81fuviYUV8DxFr3fp2dUi3ZYSo=
 github.com/hashicorp/hcl/v2 v2.18.1/go.mod h1:ThLC89FV4p9MPW804KVbe/cEXoQ8NZEh+JtMeeGErHE=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kylelemons/godebug v0.0.0-20170820004349-d65d576e9348 h1:MtvEpTB6LX3vkb4ax0b5D2DHbNAUsen0Gx5wZoq3lV4=
 github.com/mattn/go-sqlite3 v1.14.16 h1:yOQRA0RpS5PFz/oikGwBEqvAWhWg5ufRz4ETLjwpU1Y=
 github.com/mattn/go-sqlite3 v1.14.16/go.mod h1:2eHXhiwb8IkHr+BDWZGa96P6+rkvnG63S2DGjv9HUNg=
+github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0 h1:jWpvCLoY8Z/e3VKvlsiIGKtc+UG6U5vzxaoagmhXfyg=
+github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0/go.mod h1:QUyp042oQthUoa9bqDv0ER0wrtXnBruoNd7aNjkbP+k=
 github.com/mitchellh/go-wordwrap v1.0.1 h1:TLuKupo69TCn6TQSyGxwI1EblZZEsQ0vMlAFQflz0v0=
 github.com/mitchellh/go-wordwrap v1.0.1/go.mod h1:R62XHJLzvMFRBbcrT7m7WgmE1eOyTSsCt+hzestvNj0=
 github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyuac5Z2hdY=
 github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/prometheus/client_golang v1.18.0 h1:HzFfmkOzH5Q8L8G+kSJKUx5dtG87sewO+FoDDqP5Tbk=
+github.com/prometheus/client_golang v1.18.0/go.mod h1:T+GXkCk5wSJyOqMIzVgvvjFDlkOQntgjkJWKrN5txjA=
+github.com/prometheus/client_model v0.5.0 h1:VQw1hfvPvk3Uv6Qf29VrPF32JB6rtbgI6cYPYQjL0Qw=
+github.com/prometheus/client_model v0.5.0/go.mod h1:dTiFglRmd66nLR9Pv9f0mZi7B7fk5Pm3gvsjB5tr+kI=
+github.com/prometheus/common v0.45.0 h1:2BGz0eBc2hdMDLnO/8n0jeB3oPrt2D08CekT0lneoxM=
+github.com/prometheus/common v0.45.0/go.mod h1:YJmSTw9BoKxJplESWWxlbyttQR4uaEcGyv9MZjVOJsY=
+github.com/prometheus/procfs v0.12.0 h1:jluTpSng7V9hY0O2R9DzzJHYb2xULk9VTR1V1R/k6Bo=
+github.com/prometheus/procfs v0.12.0/go.mod h1:pcuDEFsWDnvcgNzo4EEweacyhjeA9Zk3cnaOZAZEfOo=
 github.com/russross/blackfriday/v2 v2.0.1/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
@@ -104,11 +119,15 @@ golang.org/x/net v0.17.0 h1:pVaXccu2ozPjCXewfr1S7xza/zcXTity9cCdXQYSjIM=
 golang.org/x/net v0.17.0/go.mod h1:NxSsAGuq816PNPmqtQdLE42eU2Fs7NoRIZrHJAlaCOE=
 golang.org/x/oauth2 v0.11.0 h1:vPL4xzxBM4niKCW6g9whtaWVXTJf1U5e4aZxxFx/gbU=
 golang.org/x/oauth2 v0.11.0/go.mod h1:LdF7O/8bLR/qWK9DrpXmbHLTouvRHK0SgJl0GmDBchk=
+golang.org/x/oauth2 v0.12.0 h1:smVPGxink+n1ZI5pkQa8y6fZT0RW0MgCO5bFpepy4B4=
+golang.org/x/oauth2 v0.12.0/go.mod h1:A74bZ3aGXgCY0qaIC9Ahg6Lglin4AMAco8cIv9baba4=
 golang.org/x/sync v0.4.0 h1:zxkM55ReGkDlKSM+Fu41A+zmbZuaPVbGMzvvdUPznYQ=
 golang.org/x/sync v0.4.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
 golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.15.0 h1:h48lPFYpsTvQJZF4EKyI4aLHaev3CxivZmv7yZig9pc=
+golang.org/x/sys v0.15.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/text v0.13.0 h1:ablQoSUd0tRdKxZewP80B+BaqeKJuVhuRxj/dkrun3k=

tavern/app.go

@@ -8,29 +8,29 @@ import (
 	"fmt"
 	"log"
 	"net/http"
-	pprof "net/http/pprof"
+	"net/http/pprof"
 	"os"
 	"strings"
 
 	"entgo.io/contrib/entgql"
-	"google.golang.org/grpc"
-	"realm.pub/tavern/internal/c2"
-	"realm.pub/tavern/internal/c2/c2pb"
-	"realm.pub/tavern/internal/graphql"
-	"realm.pub/tavern/tomes"
-
 	gqlgraphql "github.com/99designs/gqlgen/graphql"
 	"github.com/99designs/gqlgen/graphql/handler"
 	"github.com/99designs/gqlgen/graphql/playground"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/urfave/cli"
 	"golang.org/x/net/http2"
 	"golang.org/x/net/http2/h2c"
+	"google.golang.org/grpc"
 	"realm.pub/tavern/internal/auth"
+	"realm.pub/tavern/internal/c2"
+	"realm.pub/tavern/internal/c2/c2pb"
 	"realm.pub/tavern/internal/cdn"
 	"realm.pub/tavern/internal/ent"
 	"realm.pub/tavern/internal/ent/migrate"
+	"realm.pub/tavern/internal/graphql"
 	tavernhttp "realm.pub/tavern/internal/http"
 	"realm.pub/tavern/internal/www"
+	"realm.pub/tavern/tomes"
 )
 
 func newApp(ctx context.Context, options ...func(*Config)) (app *cli.App) {
@@ -50,7 +50,24 @@ func run(ctx context.Context, options ...func(*Config)) error {
 	if err != nil {
 		return err
 	}
-	defer srv.client.Close()
+	defer srv.Close()
+
+	// Start Metrics Server (if configured)
+	if srv.MetricsHTTP != nil {
+		if srv.HTTP.Addr == srv.MetricsHTTP.Addr {
+			return fmt.Errorf(
+				"tavern and metrics http must have different listen configurations (tavern=%q, metrics=%q)",
+				srv.HTTP.Addr,
+				srv.MetricsHTTP.Addr,
+			)
+		}
+		go func() {
+			log.Printf("Metrics HTTP Server started on %s", srv.MetricsHTTP.Addr)
+			if err := srv.MetricsHTTP.ListenAndServe(); err != nil {
+				log.Printf("[WARN] stopped metrics http server: %v", err)
+			}
+		}()
+	}
 
 	// Listen & Serve HTTP Traffic
 	log.Printf("Starting HTTP server on %s", srv.HTTP.Addr)
@@ -63,13 +80,15 @@ func run(ctx context.Context, options ...func(*Config)) error {
 
 // Server responsible for handling Tavern requests.
 type Server struct {
-	HTTP   *http.Server
-	client *ent.Client
+	HTTP        *http.Server
+	MetricsHTTP *http.Server
+	client      *ent.Client
 }
 
 // Close should always be called to clean up a Tavern server.
 func (srv *Server) Close() error {
 	srv.HTTP.Shutdown(context.Background())
+	srv.MetricsHTTP.Shutdown(context.Background())
 	return srv.client.Close()
 }
 
@@ -184,6 +203,12 @@ func NewServer(ctx context.Context, options ...func(*Config)) (*Server, error) {
 		client: client,
 	}
 
+	// Setup Metrics
+	if cfg.IsMetricsEnabled() {
+		log.Printf("[WARN] Metrics reporting is enabled, unauthenticated /metrics endpoint will be available at %q", EnvHTTPMetricsListenAddr.String())
+		tSrv.MetricsHTTP = newMetricsServer()
+	}
+
 	// Shutdown for Test Run & Exit
 	if cfg.IsTestRunAndExitEnabled() {
 		go func() {
@@ -227,7 +252,10 @@ func newGraphQLHandler(client *ent.Client) http.Handler {
 
 func newGRPCHandler(client *ent.Client) http.Handler {
 	c2srv := c2.New(client)
-	grpcSrv := grpc.NewServer()
+	grpcSrv := grpc.NewServer(
+		grpc.UnaryInterceptor(grpcWithUnaryMetrics),
+		grpc.StreamInterceptor(grpcWithStreamMetrics),
+	)
 	c2pb.RegisterC2Server(grpcSrv, c2srv)
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.ProtoMajor != 2 {
@@ -244,6 +272,15 @@ func newGRPCHandler(client *ent.Client) http.Handler {
 	})
 }
 
+func newMetricsServer() *http.Server {
+	router := http.NewServeMux()
+	router.Handle("/metrics", promhttp.Handler())
+	return &http.Server{
+		Addr:    EnvHTTPMetricsListenAddr.String(),
+		Handler: router,
+	}
+}
+
 func registerProfiler(router tavernhttp.RouteMap) {
 	router.HandleFunc("/debug/pprof/", pprof.Index)
 	router.HandleFunc("/debug/pprof/cmdline", pprof.Cmdline)

tavern/config.go

@@ -22,7 +22,9 @@ var (
 	EnvEnableTestRunAndExit = EnvString{"ENABLE_TEST_RUN_AND_EXIT", ""}
 
 	// EnvHTTPListenAddr sets the address (ip:port) for tavern's HTTP server to bind to.
-	EnvHTTPListenAddr = EnvString{"HTTP_LISTEN_ADDR", "0.0.0.0:80"}
+	// EnvHTTPMetricsAddr sets the address (ip:port) for the HTTP metrics server to bind to.
+	EnvHTTPListenAddr        = EnvString{"HTTP_LISTEN_ADDR", "0.0.0.0:80"}
+	EnvHTTPMetricsListenAddr = EnvString{"HTTP_METRICS_LISTEN_ADDR", "127.0.0.1:8080"}
 
 	// EnvOAuthClientID set to configure OAuth Client ID.
 	// EnvOAuthClientSecret set to configure OAuth Client Secret.
@@ -50,7 +52,9 @@ var (
 	EnvDBMaxConnLifetime = EnvInteger{"DB_MAX_CONN_LIFETIME", 3600}
 
 	// EnvEnablePProf enables performance profiling and should not be enabled in production.
-	EnvEnablePProf = EnvString{"ENABLE_PPROF", ""}
+	// EnvEnableMetrics enables the /metrics endpoint and HTTP server. It is unauthenticated and should be used carefully.
+	EnvEnablePProf   = EnvString{"ENABLE_PPROF", ""}
+	EnvEnableMetrics = EnvString{"ENABLE_METRICS", ""}
 )
 
 // Config holds information that controls the behaviour of Tavern
@@ -107,6 +111,11 @@ func (cfg *Config) Connect(options ...ent.Option) (*ent.Client, error) {
 	return ent.NewClient(append(options, ent.Driver(drv))...), nil
 }
 
+// IsMetricsEnabled returns true if the /metrics http endpoint has been enabled.
+func (cfg *Config) IsMetricsEnabled() bool {
+	return EnvEnableMetrics.String() != ""
+}
+
 // IsPProfEnabled returns true if performance profiling has been enabled.
 func (cfg *Config) IsPProfEnabled() bool {
 	return EnvEnablePProf.String() != ""

tavern/internal/c2/api_claim_tasks.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 	"realm.pub/tavern/internal/c2/c2pb"
@@ -14,6 +15,20 @@ import (
 	"realm.pub/tavern/internal/namegen"
 )
 
+var (
+	metricHostCallbacksTotal = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "tavern_host_callbacks_total",
+			Help: "The total number of ClaimTasks gRPC calls, provided with host labeling",
+		},
+		[]string{"host_identifier"},
+	)
+)
+
+func init() {
+	prometheus.MustRegister(metricHostCallbacksTotal)
+}
+
 func (srv *Server) ClaimTasks(ctx context.Context, req *c2pb.ClaimTasksRequest) (*c2pb.ClaimTasksResponse, error) {
 	now := time.Now()
 
@@ -40,6 +55,11 @@ func (srv *Server) ClaimTasks(ctx context.Context, req *c2pb.ClaimTasksRequest)
 		return nil, status.Errorf(codes.InvalidArgument, "must provide agent identifier")
 	}
 
+	// Metrics
+	defer func() {
+		metricHostCallbacksTotal.WithLabelValues(req.Beacon.Identifier).Inc()
+	}()
+
 	// Upsert the host
 	hostID, err := srv.graph.Host.Create().
 		SetIdentifier(req.Beacon.Host.Identifier).

tavern/internal/http/metrics.go

@@ -0,0 +1,27 @@
+package http
+
+import "github.com/prometheus/client_golang/prometheus"
+
+var (
+	metricHTTPRequests = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "tavern_http_requests_total",
+			Help: "Total number of requests received.",
+		},
+		[]string{"request_uri", "method"},
+	)
+
+	metricHTTPLatency = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "tavern_http_request_duration_seconds",
+			Help:    "Latency of requests.",
+			Buckets: prometheus.DefBuckets,
+		},
+		[]string{"request_uri", "method"},
+	)
+)
+
+func init() {
+	// Register metrics with Prometheus
+	prometheus.MustRegister(metricHTTPRequests, metricHTTPLatency)
+}

tavern/internal/http/server.go

@@ -2,6 +2,7 @@ package http
 
 import (
 	"net/http"
+	"time"
 )
 
 // A Server for Tavern HTTP traffic.
@@ -12,6 +13,8 @@ type Server struct {
 }
 
 func (srv *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	start := time.Now()
+
 	// Authenticate Request (if possible)
 	ctx, err := srv.Authenticate(r)
 	if err != nil {
@@ -32,6 +35,15 @@ func (srv *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 	r = r.WithContext(ctx)
 
+	// Metrics
+	defer func() {
+		// Increment total requests counter
+		metricHTTPRequests.WithLabelValues(r.RequestURI, r.Method).Inc()
+
+		// Record the latency
+		metricHTTPLatency.WithLabelValues(r.RequestURI, r.Method).Observe(time.Since(start).Seconds())
+	}()
+
 	// Log Request
 	if srv.Logger != nil {
 		srv.Log(r)

tavern/main_test.go

@@ -10,12 +10,16 @@ import (
 func TestMainFunc(t *testing.T) {
 	os.Setenv(EnvEnableTestRunAndExit.Key, "1")
 	os.Setenv(EnvHTTPListenAddr.Key, "127.0.0.1:8080")
+	os.Setenv(EnvHTTPMetricsListenAddr.Key, "127.0.0.1:8081")
 	os.Setenv(EnvEnablePProf.Key, "1")
+	os.Setenv(EnvEnableMetrics.Key, "1")
 	defer func() {
 		unsetList := []string{
 			EnvEnableTestRunAndExit.Key,
 			EnvHTTPListenAddr.Key,
+			EnvHTTPMetricsListenAddr.Key,
 			EnvEnablePProf.Key,
+			EnvEnableMetrics.Key,
 		}
 		for _, unset := range unsetList {
 			if err := os.Unsetenv(unset); err != nil {