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|
// Package metrics implement a handler and plugin that provides Prometheus metrics.
package metrics
import (
"context"
"net"
"net/http"
"sync"
"time"
"github.com/coredns/caddy"
"github.com/coredns/coredns/plugin"
"github.com/coredns/coredns/plugin/pkg/reuseport"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"
"github.com/prometheus/client_golang/prometheus/promhttp"
)
// Metrics holds the prometheus configuration. The metrics' path is fixed to be /metrics .
type Metrics struct {
Next plugin.Handler
Addr string
Reg *prometheus.Registry
ln net.Listener
lnSetup bool
mux *http.ServeMux
srv *http.Server
zoneNames []string
zoneMap map[string]struct{}
zoneMu sync.RWMutex
plugins map[string]struct{} // all available plugins, used to determine which plugin made the client write
}
// New returns a new instance of Metrics with the given address.
func New(addr string) *Metrics {
met := &Metrics{
Addr: addr,
Reg: prometheus.DefaultRegisterer.(*prometheus.Registry),
zoneMap: make(map[string]struct{}),
plugins: pluginList(caddy.ListPlugins()),
}
return met
}
// MustRegister wraps m.Reg.MustRegister.
func (m *Metrics) MustRegister(c prometheus.Collector) {
err := m.Reg.Register(c)
if err != nil {
// ignore any duplicate error, but fatal on any other kind of error
if _, ok := err.(prometheus.AlreadyRegisteredError); !ok {
log.Fatalf("Cannot register metrics collector: %s", err)
}
}
}
// AddZone adds zone z to m.
func (m *Metrics) AddZone(z string) {
m.zoneMu.Lock()
m.zoneMap[z] = struct{}{}
m.zoneNames = keys(m.zoneMap)
m.zoneMu.Unlock()
}
// RemoveZone remove zone z from m.
func (m *Metrics) RemoveZone(z string) {
m.zoneMu.Lock()
delete(m.zoneMap, z)
m.zoneNames = keys(m.zoneMap)
m.zoneMu.Unlock()
}
// ZoneNames returns the zones of m.
func (m *Metrics) ZoneNames() []string {
m.zoneMu.RLock()
s := m.zoneNames
m.zoneMu.RUnlock()
return s
}
// OnStartup sets up the metrics on startup.
func (m *Metrics) OnStartup() error {
ln, err := reuseport.Listen("tcp", m.Addr)
if err != nil {
log.Errorf("Failed to start metrics handler: %s", err)
return err
}
m.ln = ln
m.lnSetup = true
m.mux = http.NewServeMux()
m.mux.Handle("/metrics", promhttp.HandlerFor(m.Reg, promhttp.HandlerOpts{}))
// creating some helper variables to avoid data races on m.srv and m.ln
server := &http.Server{Handler: m.mux}
m.srv = server
go func() {
server.Serve(ln)
}()
ListenAddr = ln.Addr().String() // For tests.
return nil
}
// OnRestart stops the listener on reload.
func (m *Metrics) OnRestart() error {
if !m.lnSetup {
return nil
}
u.Unset(m.Addr)
return m.stopServer()
}
func (m *Metrics) stopServer() error {
if !m.lnSetup {
return nil
}
ctx, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
defer cancel()
if err := m.srv.Shutdown(ctx); err != nil {
log.Infof("Failed to stop prometheus http server: %s", err)
return err
}
m.lnSetup = false
m.ln.Close()
return nil
}
// OnFinalShutdown tears down the metrics listener on shutdown and restart.
func (m *Metrics) OnFinalShutdown() error { return m.stopServer() }
func keys(m map[string]struct{}) []string {
sx := []string{}
for k := range m {
sx = append(sx, k)
}
return sx
}
// pluginList iterates over the returned plugin map from caddy and removes the "dns." prefix from them.
func pluginList(m map[string][]string) map[string]struct{} {
pm := map[string]struct{}{}
for _, p := range m["others"] {
// only add 'dns.' plugins
if len(p) > 3 {
pm[p[4:]] = struct{}{}
continue
}
}
return pm
}
// ListenAddr is assigned the address of the prometheus listener. Its use is mainly in tests where
// we listen on "localhost:0" and need to retrieve the actual address.
var ListenAddr string
// shutdownTimeout is the maximum amount of time the metrics plugin will wait
// before erroring when it tries to close the metrics server
const shutdownTimeout time.Duration = time.Second * 5
var buildInfo = promauto.NewGaugeVec(prometheus.GaugeOpts{
Namespace: plugin.Namespace,
Name: "build_info",
Help: "A metric with a constant '1' value labeled by version, revision, and goversion from which CoreDNS was built.",
}, []string{"version", "revision", "goversion"})
|
