From 33e83108690d3a1c1262fe755774632855009702 Mon Sep 17 00:00:00 2001
From: Botond Szirtes <botond.szirtes@est.tech>
Date: Mon, 29 Jul 2024 13:37:55 +0200
Subject: [PATCH] Add an option to expose Prometheus metrics via http/s server

Signed-off-by: Botond Szirtes <botond.szirtes@est.tech>
---
 go.mod                                   |  2 +-
 pkg/tools/opentelemetry/opentelemetry.go | 13 +++-
 pkg/tools/opentelemetry/server.go        | 81 ++++++++++++++++++++++++
 3 files changed, 94 insertions(+), 2 deletions(-)
 create mode 100644 pkg/tools/opentelemetry/server.go

diff --git a/go.mod b/go.mod
index 893943358..e16b32f94 100644
--- a/go.mod
+++ b/go.mod
@@ -22,6 +22,7 @@ require (
 	github.com/networkservicemesh/api v1.13.1-0.20240424210452-d0df98851760
 	github.com/open-policy-agent/opa v0.44.0
 	github.com/pkg/errors v0.9.1
+	github.com/prometheus/client_golang v1.17.0
 	github.com/r3labs/diff v1.1.0
 	github.com/sirupsen/logrus v1.9.0
 	github.com/spiffe/go-spiffe/v2 v2.1.7
@@ -85,7 +86,6 @@ require (
 	github.com/nats-io/nuid v1.0.1 // indirect
 	github.com/openzipkin/zipkin-go v0.4.2 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/prometheus/client_golang v1.17.0 // indirect
 	github.com/prometheus/client_model v0.5.0 // indirect
 	github.com/prometheus/common v0.44.0 // indirect
 	github.com/prometheus/procfs v0.11.1 // indirect
diff --git a/pkg/tools/opentelemetry/opentelemetry.go b/pkg/tools/opentelemetry/opentelemetry.go
index aa8b75cca..abf4abddc 100644
--- a/pkg/tools/opentelemetry/opentelemetry.go
+++ b/pkg/tools/opentelemetry/opentelemetry.go
@@ -2,6 +2,8 @@
 //
 // Copyright (c) 2023 Cisco and/or its affiliates.
 //
+// Copyright (c) 2024 Nordix Foundation.
+//
 // SPDX-License-Identifier: Apache-2.0
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -36,7 +38,8 @@ import (
 )
 
 const (
-	telemetryEnv = "TELEMETRY"
+	telemetryEnv  = "TELEMETRY"
+	prometheusEnv = "PROMETHEUS"
 )
 
 // IsEnabled returns true if opentelemetry enabled
@@ -47,6 +50,14 @@ func IsEnabled() bool {
 	return false
 }
 
+// IsPrometheusEnabled returns true if prometheus enabled
+func IsPrometheusEnabled() bool {
+	if v, err := strconv.ParseBool(os.Getenv(prometheusEnv)); err == nil {
+		return v
+	}
+	return false
+}
+
 type opentelemetry struct {
 	io.Closer
 
diff --git a/pkg/tools/opentelemetry/server.go b/pkg/tools/opentelemetry/server.go
new file mode 100644
index 000000000..e28d1cf1e
--- /dev/null
+++ b/pkg/tools/opentelemetry/server.go
@@ -0,0 +1,81 @@
+// Copyright (c) 2024 Nordix Foundation.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at:
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package opentelemetry provides a set of utilities for assisting with telemetry data
+package opentelemetry
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+
+	"github.com/networkservicemesh/sdk/pkg/tools/log"
+)
+
+// Server is a server type for handling requests
+type Server struct {
+	IP            string
+	TLSCertFile   string
+	TLSKeyFile    string
+	Port          int
+	HeaderTimeout time.Duration
+}
+
+// Start initiates the server to begin handling incoming requests
+func (s *Server) Start(ctx context.Context) error {
+	log.FromContext(ctx).Info("Start metrics server", "ip", s.IP, "port", s.Port)
+
+	server := &http.Server{
+		Addr:              fmt.Sprintf("%s:%d", s.IP, s.Port),
+		ReadHeaderTimeout: s.HeaderTimeout,
+	}
+
+	http.Handle("/metrics", promhttp.Handler())
+
+	serverCtx, cancel := context.WithCancel(ctx)
+	var ListenAndServeErr error
+
+	go func() {
+		if s.TLSCertFile != "" && s.TLSKeyFile != "" {
+			ListenAndServeErr = server.ListenAndServeTLS(s.TLSCertFile, s.TLSKeyFile)
+		} else {
+			ListenAndServeErr = server.ListenAndServe()
+		}
+		if ListenAndServeErr != nil {
+			cancel()
+		}
+	}()
+
+	<-serverCtx.Done()
+
+	if ListenAndServeErr != nil {
+		return errors.Errorf("failed to ListenAndServe on metrics server: %s", ListenAndServeErr)
+	}
+
+	shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer shutdownCancel()
+
+	err := server.Shutdown(shutdownCtx)
+	if err != nil {
+		return errors.Errorf("failed to shutdown metrics server: %s", err)
+	}
+
+	return nil
+}