config-reloader的源码：https://github.com/prometheus...
config-reloader的启动参数：
prometheus-config-reloader:Image: 178.104.162.39:443/kubernetes/amd64/prometheus-config-reloader:v0.40.0Args: --log-format=logfmt --reload-url=http://localhost:9090/-/reload --config-file=/etc/prometheus/config/prometheus.yaml.gz --config-envsubst-file=/etc/prometheus/config_out/prometheus.env.yamloperator监听到prometheus配置变更，会更新secret(文件prometheus-yaml.gz，应用gz保障<1M)，config-reloader监控到prometheus-yaml.gz文件有变更，将其解压至prometheus-env.yaml，而后发送reload给prometehus。
1. config-reloader内的源码剖析
代码中监听了config-file和rules-dir(未应用)的变动：
// cmd/promethues-config-reloader/main.gofunc main() { cfgFile := app.Flag("config-file", "config file watched by the reloader").String() cfgSubstFile := app.Flag("config-envsubst-file", "output file for environment variable substituted config file").String() rulesDir := app.Flag("rules-dir", "Rules directory to watch non-recursively").Strings() var g run.Group { ctx, cancel := context.WithCancel(context.Background()) rel := reloader.New(logger, *reloadURL, *cfgFile, *cfgSubstFile, *rulesDir) g.Add(func() error { return rel.Watch(ctx) }, func(error) { cancel() }) } if err := g.Run(); err != nil { fmt.Fprintln(os.Stderr, err) os.Exit(1) }}监听的动作由reloader实现：
// New creates a new reloader that watches the given config file and rule directory// and triggers a Prometheus reload upon changes.// If cfgOutputFile is not empty the config file will be decompressed if needed, environment variables// will be substituted and the output written into the given path. Prometheus should then use// cfgOutputFile as its config file path.func New(logger log.Logger, reloadURL *url.URL, cfgFile string, cfgOutputFile string, ruleDirs []string) *Reloader { if logger == nil { logger = log.NewNopLogger() } return &Reloader{ logger: logger, reloadURL: reloadURL, cfgFile: cfgFile, cfgOutputFile: cfgOutputFile, ruleDirs: ruleDirs, watchInterval: 3 * time.Minute, retryInterval: 5 * time.Second, }}能够看到reloader每个3min监听一次变动，应用fsnotify监听文件的变动：
// Watch starts to watch periodically the config file and rules and process them until the context// gets canceled. Config file gets env expanded if cfgOutputFile is specified and reload is trigger if// config or rules changed.// Watch watchers periodically based on r.watchInterval.// For config file it watches it directly as well via fsnotify.// It watches rule dirs as well, but lot's of edge cases are missing, so rely on interval mostly.func (r *Reloader) Watch(ctx context.Context) error { // 应用fsnotity监听 watcher, err := fsnotify.NewWatcher() // 监听cfgFile watchables := map[string]struct{}{} if r.cfgFile != "" { watchables[filepath.Dir(r.cfgFile)] = struct{}{} if err := watcher.Add(r.cfgFile); err != nil { return errors.Wrapf(err, "add config file %s to watcher", r.cfgFile) } if err := r.apply(ctx); err != nil { return err } } tick := time.NewTicker(r.watchInterval) defer tick.Stop() for { select { case <-ctx.Done(): return nil case <-tick.C: case event := <-watcher.Events: // TODO(bwplotka): Add metric if we are not cycling CPU here too much. if _, ok := watchables[filepath.Dir(event.Name)]; !ok { continue } case err := <-watcher.Errors: level.Error(r.logger).Log("msg", "watch error", "err", err) continue } // 监听到变动，apply if err := r.apply(ctx); err != nil { // Critical error. return err } }}监听到变动会apply，apply中波及的文件：
- r.cfgFile=/etc/prometheus/config/prometheus.yaml.gz，它是1个gzip文件;
- r.cfgOutputFile=/etc/prometheus/config_out/prometheus.env.yaml，它是真正被prometheus挂载应用的配置文件;
apply中的文件操作：
- gunzip解压缩cfgFile文件；
- 将解压缩的文件内容，写入到cfgOutputFile；
- 也就说，gz文件是最新的配置，它被解压缩而后替换env，最终生成新的配置文件promethues-env.yaml；
// thanos-io/thanos/pkg/reloader/reloader.go// apply triggers Prometheus reload if rules or config changed. If cfgOutputFile is set, we also// expand env vars into config file before reloading.// Reload is retried in retryInterval until watchInterval.func (r *Reloader) apply(ctx context.Context) error { if r.cfgFile != "" { if r.cfgOutputFile != "" { b, err := ioutil.ReadFile(r.cfgFile) if err != nil { return errors.Wrap(err, "read file") } // cfgFile是个gz文件，读文件内容 // Detect and extract gzipped file. if bytes.Equal(b[0:3], firstGzipBytes) { zr, err := gzip.NewReader(bytes.NewReader(b)) if err != nil { return errors.Wrap(err, "create gzip reader") } defer runutil.CloseWithLogOnErr(r.logger, zr, "gzip reader close") b, err = ioutil.ReadAll(zr) if err != nil { return errors.Wrap(err, "read compressed config file") } } // 替换其中的env变量为实在值 b, err = expandEnv(b) if err != nil { return errors.Wrap(err, "expand environment variables") } tmpFile := r.cfgOutputFile + ".tmp" defer func() { _ = os.Remove(tmpFile) }() // 将cfgFile的内容，写入cfgOutputFile if err := ioutil.WriteFile(tmpFile, b, 0666); err != nil { return errors.Wrap(err, "write file") } if err := os.Rename(tmpFile, r.cfgOutputFile); err != nil { return errors.Wrap(err, "rename file") } } } // 向prometheus发送reload if err := runutil.RetryWithLog(r.logger, r.retryInterval, retryCtx.Done(), func() error { if err := r.triggerReload(ctx); err != nil { return errors.Wrap(err, "trigger reload") } .... }}apply中的reload操作：POST reloadURL告诉prometheus配置变更；
// thanos-io/thanos/pkg/reloader/reloader.gofunc (r *Reloader) triggerReload(ctx context.Context) error { req, err := http.NewRequest("POST", r.reloadURL.String(), nil) if err != nil { return errors.Wrap(err, "create request") } req = req.WithContext(ctx) resp, err := http.DefaultClient.Do(req) if err != nil { return errors.Wrap(err, "reload request failed") } defer runutil.ExhaustCloseWithLogOnErr(r.logger, resp.Body, "trigger reload resp body") if resp.StatusCode != 200 { return errors.Errorf("received non-200 response: %s; have you set `--web.enable-lifecycle` Prometheus flag?", resp.Status) } return nil}2. config-reloader中prometheus.yaml.gz的由来
prometheus.yaml.gz是gzip文件，依据下面的剖析，config-reloader每隔3min监听一次prometheus.yaml.gz文件的变动，而后将其gunzip再写入到prometheus-env.yaml，给prometheus应用。
那么，prometheus.yaml.gz文件是哪里来的，为什么要应用gz文件？
能够在prometheus-operator中找到答案：
- prometheus.yaml.gz是secret(prometheus-k8s)挂载而来，该secret由operator保护；
- 应用gz文件是因为secret有1M大小的限度，避免文件过大；
operator保护secret(prometheus-k8s):
- 当prometheus CRD对象产生变更时，产生变更事件，而后由goroutine在sync中生产；
- operator依据promethues CRD对象的配置，生成secret spec；
- 如果secret不存在，则sClient.Create(); 否则sClient.Update()；
// pkg/prometheus/operator.gofunc (c *Operator) sync(key string) error { ... if err := c.createOrUpdateConfigurationSecret(p, ruleConfigMapNames); err != nil { return errors.Wrap(err, "creating config failed") } ...}// pkg/prometheus/operator.gofunc (c *Operator) createOrUpdateConfigurationSecret(p *monitoringv1.Prometheus, ruleConfigMapNames []string) error { ...... // Update secret based on the most recent configuration. conf, err := c.configGenerator.generateConfig( p, smons, pmons, basicAuthSecrets, bearerTokens, additionalScrapeConfigs, additionalAlertRelabelConfigs, additionalAlertManagerConfigs, ruleConfigMapNames, ) // 生成secrete的spec s := makeConfigSecret(p, c.config) s.ObjectMeta.Annotations = map[string]string{ "generated": "true", } ...... // gz的起因在这里 // Compress config to avoid 1mb secret limit for a while var buf bytes.Buffer if err = gzipConfig(&buf, conf); err != nil { return errors.Wrap(err, "couldnt gzip config") } // 这里configFilename="prometheus.yaml.gz" s.Data[configFilename] = buf.Bytes() // secret不存在的话，Create，而后返回 curSecret, err := sClient.Get(context.TODO(), s.Name, metav1.GetOptions{}) if apierrors.IsNotFound(err) { level.Debug(c.logger).Log("msg", "creating configuration") _, err = sClient.Create(context.TODO(), s, metav1.CreateOptions{}) return err } ...... // secret已存在，Update level.Debug(c.logger).Log("msg", "updating Prometheus configuration secret") _, err = sClient.Update(context.TODO(), s, metav1.UpdateOptions{}) return err}