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reloader.go
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reloader.go
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// Copyright 2022-2024 The Parca 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 config
import (
"context"
"errors"
"fmt"
"time"
"github.com/fsnotify/fsnotify"
"github.com/go-kit/log"
"github.com/go-kit/log/level"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"
)
// ComponentReloader describes how to reload a component.
type ComponentReloader struct {
Name string
Reloader func(*Config) error
}
// ConfigReloader holds all information required to reload Parca Agent's config into its running components.
type ConfigReloader struct {
logger log.Logger
filename string
watcher *fsnotify.Watcher
reloaders []ComponentReloader
triggerReload chan struct{}
configSuccess prometheus.Gauge
configSuccessTime prometheus.Gauge
}
// NewConfigReloader returns an instantiated config reloader.
func NewConfigReloader(
logger log.Logger,
reg prometheus.Registerer,
filename string,
reloaders []ComponentReloader,
) (*ConfigReloader, error) {
watcher, err := fsnotify.NewWatcher()
if err != nil {
level.Error(logger).Log("msg", "failed to establish config watcher", "err", err)
return nil, err
}
if err := watcher.Add(filename); err != nil {
level.Error(logger).Log("msg", "failed to start watching config file", "err", err, "path", filename)
return nil, err
}
r := &ConfigReloader{
logger: logger,
filename: filename,
watcher: watcher,
reloaders: reloaders,
triggerReload: make(chan struct{}, 1),
configSuccess: promauto.With(reg).NewGauge(prometheus.GaugeOpts{
Name: "parca_agent_config_last_reload_successful",
Help: "Whether the last configuration reload attempt was successful.",
}),
configSuccessTime: promauto.With(reg).NewGauge(prometheus.GaugeOpts{
Name: "parca_agent_config_last_reload_success_timestamp_seconds",
Help: "Timestamp of the last successful configuration reload.",
}),
}
return r, nil
}
func (r *ConfigReloader) watchFile() {
for {
select {
case event, ok := <-r.watcher.Events:
if !ok {
level.Debug(r.logger).Log("msg", "config file watcher events channel closed. exiting goroutine.")
return
}
if event.Has(fsnotify.Remove) {
// Handle case where the config file is a symlink (e.g. Kubernetes ConfigMap)
level.Debug(r.logger).Log("msg", "config file has been removed/recreated")
// Ensure watcher has stopped monitoring the removed file
if err := r.watcher.Remove(event.Name); err != nil && !errors.Is(err, fsnotify.ErrNonExistentWatch) {
level.Error(r.logger).Log("msg", "failed to stop watching old config file", "err", err, "path", r.filename)
return
}
// Watch new file (fsnotify follows symlinks)
if err := r.watcher.Add(r.filename); err != nil {
level.Error(r.logger).Log("msg", "failed to start watching new config file", "err", err, "path", r.filename)
return
}
r.triggerReload <- struct{}{}
} else if event.Has(fsnotify.Write) {
level.Debug(r.logger).Log("msg", "config file has been modified")
r.triggerReload <- struct{}{}
}
case err, ok := <-r.watcher.Errors:
if !ok {
level.Debug(r.logger).Log("msg", "config file watcher errors channel closed. exiting goroutine.")
return
}
level.Error(r.logger).Log("msg", "error encountered while watching config file", "err", err)
}
}
}
//nolint:nonamedreturns
func (r *ConfigReloader) reloadFile() (err error) {
start := time.Now()
timings := []interface{}{}
level.Info(r.logger).Log("msg", "loading configuration file", "filename", r.filename)
defer func() {
if err == nil {
r.configSuccess.Set(1)
r.configSuccessTime.SetToCurrentTime()
} else {
r.configSuccess.Set(0)
}
}()
cfg, err := LoadFile(r.filename)
if err != nil {
return fmt.Errorf("failed to load configuration: %w", err)
}
failed := false
for _, rl := range r.reloaders {
rstart := time.Now()
if err := rl.Reloader(cfg); err != nil {
level.Error(r.logger).Log("msg", "failed to apply configuration", "err", err)
failed = true
}
timings = append(timings, rl.Name, time.Since(rstart))
}
if failed {
return fmt.Errorf("one or more errors occurred while applying the new configuration (--config-path=%q)", r.filename)
}
l := []interface{}{"msg", "completed loading of configuration file", "filename", r.filename, "totalDuration", time.Since(start)}
level.Info(r.logger).Log(append(l, timings...)...)
return nil
}
// Run starts watching the config file and wait for reload triggers.
func (r *ConfigReloader) Run(ctx context.Context) error {
go r.watchFile()
for {
select {
case <-r.triggerReload:
if err := r.reloadFile(); err != nil {
level.Error(r.logger).Log("msg", "failed to reload configuration file", "err", err)
}
case <-ctx.Done():
r.watcher.Close()
return nil
}
}
}