prometheus/discovery/file/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 file
import (
"encoding/json"
"fmt"
"io/ioutil"
"path/filepath"
"strings"
"time"
"github.com/prometheus/client_golang/prometheus"
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"github.com/prometheus/common/log"
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"github.com/prometheus/common/model"
"golang.org/x/net/context"
"gopkg.in/fsnotify.v1"
"gopkg.in/yaml.v2"
"github.com/prometheus/prometheus/config"
)
const fileSDFilepathLabel = model.MetaLabelPrefix + "filepath"
var (
fileSDScanDuration = prometheus.NewSummary(
prometheus.SummaryOpts{
Name: "prometheus_sd_file_scan_duration_seconds",
Help: "The duration of the File-SD scan in seconds.",
})
fileSDReadErrorsCount = prometheus.NewCounter(
prometheus.CounterOpts{
Name: "prometheus_sd_file_read_errors_total",
Help: "The number of File-SD read errors.",
})
)
func init() {
prometheus.MustRegister(fileSDScanDuration)
prometheus.MustRegister(fileSDReadErrorsCount)
}
// 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
}
// NewDiscovery returns a new file discovery for the given paths.
func NewDiscovery(conf *config.FileSDConfig) *FileDiscovery {
return &FileDiscovery{
paths: conf.Files,
interval: time.Duration(conf.RefreshInterval),
}
}
// 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(ctx context.Context, ch chan<- []*config.TargetGroup) {
defer fd.stop()
watcher, err := fsnotify.NewWatcher()
if err != nil {
log.Errorf("Error creating file watcher: %s", err)
return
}
fd.watcher = watcher
fd.refresh(ctx, ch)
ticker := time.NewTicker(fd.interval)
defer ticker.Stop()
for {
select {
case <-ctx.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(ctx, ch)
case <-ticker.C:
// Setting a new watch after an update might fail. Make sure we don't lose
// those files forever.
fd.refresh(ctx, ch)
case err := <-fd.watcher.Errors:
if err != nil {
log.Errorf("Error on file watch: %s", err)
}
}
}
}
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// stop shuts down the file watcher.
func (fd *FileDiscovery) stop() {
log.Debugf("Stopping file discovery for %s...", fd.paths)
done := make(chan struct{})
defer close(done)
// 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.
case <-done:
return
}
}
}()
if err := fd.watcher.Close(); err != nil {
log.Errorf("Error closing file watcher for %s: %s", fd.paths, err)
}
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log.Debugf("File discovery for %s stopped.", fd.paths)
}
// refresh reads all files matching the discovery's patterns and sends the respective
// updated target groups through the channel.
func (fd *FileDiscovery) refresh(ctx context.Context, ch chan<- []*config.TargetGroup) {
t0 := time.Now()
defer func() {
fileSDScanDuration.Observe(time.Since(t0).Seconds())
}()
ref := map[string]int{}
for _, p := range fd.listFiles() {
tgroups, err := readFile(p)
if err != nil {
fileSDReadErrorsCount.Inc()
log.Errorf("Error reading file %q: %s", p, err)
// Prevent deletion down below.
ref[p] = fd.lastRefresh[p]
continue
}
select {
case ch <- tgroups:
case <-ctx.Done():
return
}
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++ {
select {
case ch <- []*config.TargetGroup{{Source: fileSource(f, i)}}:
case <-ctx.Done():
return
}
}
}
}
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)
}
// 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 = model.LabelSet{}
}
tg.Labels[fileSDFilepathLabel] = model.LabelValue(filename)
}
return targetGroups, nil
}