/
server.go
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/
server.go
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// Copyright 2017 Istio Authors
//
// 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 prometheus
import (
"context"
"fmt"
"io"
"net"
"net/http"
"sync"
"time"
"istio.io/istio/mixer/pkg/adapter"
)
type (
// Server presents prometheus server endpoint
Server interface {
io.Closer
Start(adapter.Env, http.Handler) error
Port() int
}
serverInst struct {
addr string
lock sync.Mutex // protects resources below
srv *http.Server
handler *metaHandler
refCnt int
port int // port that this server instance is listening on
}
)
const (
metricsPath = "/metrics"
defaultAddr = ":42422"
)
func newServer(addr string) *serverInst {
return &serverInst{addr: addr}
}
// metaHandler switches the delegate without downtime.
type metaHandler struct {
delegate http.Handler
lock sync.RWMutex
}
func (m *metaHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
m.lock.RLock()
m.delegate.ServeHTTP(w, r)
m.lock.RUnlock()
}
func (m *metaHandler) setDelegate(delegate http.Handler) {
m.lock.Lock()
m.delegate = delegate
m.lock.Unlock()
}
func (s *serverInst) Port() int {
return s.port
}
// Start the prometheus singleton listener.
func (s *serverInst) Start(env adapter.Env, metricsHandler http.Handler) (err error) {
s.lock.Lock()
defer s.lock.Unlock()
// if server is already running,
// just switch the delegate handler.
if s.srv != nil {
s.refCnt++
s.handler.setDelegate(metricsHandler)
return nil
}
listener, err := net.Listen("tcp", s.addr)
if err != nil {
return fmt.Errorf("could not start prometheus metrics server: %v", err)
}
s.port = listener.Addr().(*net.TCPAddr).Port
srvMux := http.NewServeMux()
s.handler = &metaHandler{delegate: metricsHandler}
srvMux.Handle(metricsPath, s.handler)
srv := &http.Server{Addr: s.addr, Handler: srvMux}
env.ScheduleDaemon(func() {
env.Logger().Infof("serving prometheus metrics on %d", s.port)
if err := srv.Serve(listener.(*net.TCPListener)); err != nil {
if err == http.ErrServerClosed {
env.Logger().Infof("HTTP server stopped")
} else {
_ = env.Logger().Errorf("prometheus HTTP server error: %v", err) // nolint: gas
}
}
})
s.srv = srv
s.refCnt++
return nil
}
// Close -- closes the HTTP server if reference Count is 0.
func (s *serverInst) Close() error {
s.lock.Lock()
defer s.lock.Unlock()
// not started yet, nothing to close.
if s.srv == nil {
return nil
}
s.refCnt--
if s.refCnt > 0 {
return nil
}
// reference count is 0, cleanup.
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
srv := s.srv
s.srv = nil
s.handler = nil
return srv.Shutdown(ctx)
}