prometheus/prom/retrieval/discovery/file.go

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// Copyright 2015 The Prometheus 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 discovery
import (
"encoding/json"
"fmt"
"io/ioutil"
"path/filepath"
"strings"
"time"
"github.com/prometheus/log"
"gopkg.in/fsnotify.v1"
"gopkg.in/yaml.v2"
clientmodel "github.com/prometheus/client_golang/model"
"github.com/prometheus/prometheus/config"
)
const FileSDFilepathLabel = clientmodel.MetaLabelPrefix + "filepath"
// FileDiscovery provides service discovery functionality based
// on files that contain target groups in JSON or YAML format. Refreshing
// happens using file watches and periodic refreshes.
type FileDiscovery struct {
paths []string
watcher *fsnotify.Watcher
interval time.Duration
// lastRefresh stores which files were found during the last refresh
// and how many target groups they contained.
// This is used to detect deleted target groups.
lastRefresh map[string]int
}
// NewFileDiscovery returns a new file discovery for the given paths.
func NewFileDiscovery(conf *config.FileSDConfig) *FileDiscovery {
return &FileDiscovery{
paths: conf.Names,
interval: time.Duration(conf.RefreshInterval),
}
}
// Sources implements the TargetProvider interface.
func (fd *FileDiscovery) Sources() []string {
var srcs []string
// As we allow multiple target groups per file we have no choice
// but to parse them all.
for _, p := range fd.listFiles() {
tgroups, err := readFile(p)
if err != nil {
log.Errorf("Error reading file %q: ", p, err)
}
for _, tg := range tgroups {
srcs = append(srcs, tg.Source)
}
}
return srcs
}
// listFiles returns a list of all files that match the configured patterns.
func (fd *FileDiscovery) listFiles() []string {
var paths []string
for _, p := range fd.paths {
files, err := filepath.Glob(p)
if err != nil {
log.Errorf("Error expanding glob %q: %s", p, err)
continue
}
paths = append(paths, files...)
}
return paths
}
// watchFiles sets watches on all full paths or directories that were configured for
// this file discovery.
func (fd *FileDiscovery) watchFiles() {
if fd.watcher == nil {
panic("no watcher configured")
}
for _, p := range fd.paths {
if idx := strings.LastIndex(p, "/"); idx > -1 {
p = p[:idx]
} else {
p = "./"
}
if err := fd.watcher.Add(p); err != nil {
log.Errorf("Error adding file watch for %q: %s", p, err)
}
}
}
// Run implements the TargetProvider interface.
func (fd *FileDiscovery) Run(ch chan<- *config.TargetGroup, done <-chan struct{}) {
defer close(ch)
defer fd.stop()
watcher, err := fsnotify.NewWatcher()
if err != nil {
log.Errorf("Error creating file watcher: %s", err)
return
}
fd.watcher = watcher
fd.refresh(ch)
ticker := time.NewTicker(fd.interval)
defer ticker.Stop()
for {
// Stopping has priority over refreshing. Thus we wrap the actual select
// clause to always catch done signals.
select {
case <-done:
return
default:
select {
case <-done:
return
case event := <-fd.watcher.Events:
// fsnotify sometimes sends a bunch of events without name or operation.
// It's unclear what they are and why they are sent - filter them out.
if len(event.Name) == 0 {
break
}
// Everything but a chmod requires rereading.
if event.Op^fsnotify.Chmod == 0 {
break
}
// Changes to a file can spawn various sequences of events with
// different combinations of operations. For all practical purposes
// this is inaccurate.
// The most reliable solution is to reload everything if anything happens.
fd.refresh(ch)
case <-ticker.C:
// Setting a new watch after an update might fail. Make sure we don't lose
// those files forever.
fd.refresh(ch)
case err := <-fd.watcher.Errors:
if err != nil {
log.Errorf("Error on file watch: %s", err)
}
}
}
}
}
// refresh reads all files matching the discoveries patterns and sends the respective
// updated target groups through the channel.
func (fd *FileDiscovery) refresh(ch chan<- *config.TargetGroup) {
ref := map[string]int{}
for _, p := range fd.listFiles() {
tgroups, err := readFile(p)
if err != nil {
log.Errorf("Error reading file %q: %s", p, err)
// Prevent deletion down below.
ref[p] = fd.lastRefresh[p]
continue
}
for _, tg := range tgroups {
ch <- tg
}
ref[p] = len(tgroups)
}
// Send empty updates for sources that disappeared.
for f, n := range fd.lastRefresh {
m, ok := ref[f]
if !ok || n > m {
for i := m; i < n; i++ {
ch <- &config.TargetGroup{Source: fileSource(f, i)}
}
}
}
fd.lastRefresh = ref
fd.watchFiles()
}
// fileSource returns a source ID for the i-th target group in the file.
func fileSource(filename string, i int) string {
return fmt.Sprintf("%s:%d", filename, i)
}
// stop shuts down the file watcher.
func (fd *FileDiscovery) stop() {
log.Debugf("Stopping file discovery for %s...", fd.paths)
// Closing the watcher will deadlock unless all events and errors are drained.
go func() {
for {
select {
case <-fd.watcher.Errors:
case <-fd.watcher.Events:
// Drain all events and errors.
default:
return
}
}
}()
fd.watcher.Close()
log.Debugf("File discovery for %s stopped.", fd.paths)
}
// readFile reads a JSON or YAML list of targets groups from the file, depending on its
// file extension. It returns full configuration target groups.
func readFile(filename string) ([]*config.TargetGroup, error) {
content, err := ioutil.ReadFile(filename)
if err != nil {
return nil, err
}
var targetGroups []*config.TargetGroup
switch ext := filepath.Ext(filename); strings.ToLower(ext) {
case ".json":
if err := json.Unmarshal(content, &targetGroups); err != nil {
return nil, err
}
case ".yml", ".yaml":
if err := yaml.Unmarshal(content, &targetGroups); err != nil {
return nil, err
}
default:
panic(fmt.Errorf("retrieval.FileDiscovery.readFile: unhandled file extension %q", ext))
}
for i, tg := range targetGroups {
tg.Source = fileSource(filename, i)
if tg.Labels == nil {
tg.Labels = clientmodel.LabelSet{}
}
tg.Labels[FileSDFilepathLabel] = clientmodel.LabelValue(filename)
}
return targetGroups, nil
}