(1) Storage组件初始化
Prometheus的Storage组件是时序数据库，包含两个：localStorage和remoteStorage．localStorage当前版本指TSDB，用于对metrics的本地存储存储，remoteStorage用于metrics的远程存储，其中fanoutStorage作为localStorage和remoteStorage的读写代理服务器．初始化流程如下
prometheus/cmd/prometheus/main.go localStorage = &tsdb.ReadyStorage{} //本地存储 remoteStorage = remote.NewStorage(log.With(logger, "component", "remote"), //远端存储 localStorage.StartTime, time.Duration(cfg.RemoteFlushDeadline)) fanoutStorage = storage.NewFanout(logger, localStorage, remoteStorage) //读写代理服务器(2) notifier 组件初始化
notifier组件用于发送告警信息给AlertManager，通过方法notifier.NewManager完成初始化
prometheus/cmd/prometheus/main.go notifierManager = notifier.NewManager(&cfg.notifier, log.With(logger, "component", "notifier"))(3) discoveryManagerScrape组件初始化
discoveryManagerScrape组件用于服务发现，当前版本支持多种服务发现系统，比如kuberneters等，通过方法discovery.NewManager完成初始化，
prometheus/cmd/prometheus/main.go discoveryManagerScrape = discovery.NewManager(ctxScrape, log.With(logger, "component", "discovery manager scrape"), discovery.Name("scrape"))(4) discoveryManagerNotify组件初始化
discoveryManagerNotify组件用于告警通知服务发现，比如AlertManager服务．也是通过方法discovery.NewManager完成初始化，不同的是，discoveryManagerNotify服务于notify，而discoveryManagerScrape服务与scrape
prometheus/cmd/prometheus/main.go discoveryManagerNotify = discovery.NewManager(ctxNotify, log.With(logger, "component", "discovery manager notify"), discovery.Name("notify")(5) scrapeManager组件初始化
scrapeManager组件利用discoveryManagerScrape组件发现的targets，抓取对应targets的所有metrics，并将抓取的metrics存储到fanoutStorage中，通过方法scrape.NewManager完成初始化
prometheus/cmd/prometheus/main.go scrapeManager = scrape.NewManager(log.With(logger, "component", "scrape manager"), fanoutStorage)(6) queryEngine组件
queryEngine组件用于rules查询和计算，通过方法promql.NewEngine完成初始化
prometheus/cmd/prometheus/main.go opts = promql.EngineOpts{ Logger: log.With(logger, "component", "query engine"), Reg: prometheus.DefaultRegisterer, MaxConcurrent: cfg.queryConcurrency, //最大并发查询个数 MaxSamples: cfg.queryMaxSamples, Timeout: time.Duration(cfg.queryTimeout), //查询超时时间 } queryEngine = promql.NewEngine(opts)(7) ruleManager组件初始化
ruleManager组件通过方法rules.NewManager完成初始化．其中rules.NewManager的参数涉及多个组件：存储，queryEngine和notifier，整个流程包含rule计算和发送告警
prometheus/cmd/prometheus/main.go ruleManager = rules.NewManager(&rules.ManagerOptions{ Appendable: fanoutStorage, //存储器 TSDB: localStorage, //本地时序数据库TSDB QueryFunc: rules.EngineQueryFunc(queryEngine, fanoutStorage), //rules计算 NotifyFunc: sendAlerts(notifierManager, cfg.web.ExternalURL.String()), //告警通知 Context: ctxRule, //用于控制ruleManager组件的协程 ExternalURL: cfg.web.ExternalURL, //通过Web对外开放的URL Registerer: prometheus.DefaultRegisterer, Logger: log.With(logger, "component", "rule manager"), OutageTolerance: time.Duration(cfg.outageTolerance), //当prometheus重启时，保持alert状态（https://ganeshvernekar.com/gsoc-2018/persist-for-state/） ForGracePeriod: time.Duration(cfg.forGracePeriod), ResendDelay: time.Duration(cfg.resendDelay), }(8) Web组件初始化
Web组件用于为Storage组件，queryEngine组件，scrapeManager组件， ruleManager组件和notifier 组件提供外部HTTP访问方式，初始化代码如下
prometheus/cmd/prometheus/main.go cfg.web.Context = ctxWeb cfg.web.TSDB = localStorage.Get cfg.web.Storage = fanoutStorage cfg.web.QueryEngine = queryEngine cfg.web.ScrapeManager = scrapeManager cfg.web.RuleManager = ruleManager cfg.web.Notifier = notifierManager cfg.web.Version = &web.PrometheusVersion{ Version: version.Version, Revision: version.Revision, Branch: version.Branch, BuildUser: version.BuildUser, BuildDate: version.BuildDate, GoVersion: version.GoVersion, } cfg.web.Flags = map[string]string{} // Depends on cfg.web.ScrapeManager so needs to be after cfg.web.ScrapeManager = scrapeManager webHandler := web.New(log.With(logger, "component", "web"), &cfg.web)以上五个服务组件在Web页面对外的访问如图所示：
(1) 通过以下代码，可以发现，除了服务组件ruleManager用的方法是Update，其他服务组件的在匿名函数中通过各自的ApplyConfig方法，实现配置的管理
prometheus/cmd/prometheus/main.go reloaders := []func(cfg *config.Config) error{ remoteStorage.ApplyConfig, //存储配置 webHandler.ApplyConfig, //web配置 notifierManager.ApplyConfig, //notifier配置 scrapeManager.ApplyConfig, //scrapeManger配置 //从配置文件中提取Section:scrape_configs func(cfg *config.Config) error { c := make(map[string]sd_config.ServiceDiscoveryConfig) for _, v := range cfg.ScrapeConfigs { c[v.JobName] = v.ServiceDiscoveryConfig } return discoveryManagerScrape.ApplyConfig(c) }, //从配置文件中提取Section:alerting func(cfg *config.Config) error { c := make(map[string]sd_config.ServiceDiscoveryConfig) for _, v := range cfg.AlertingConfig.AlertmanagerConfigs { // AlertmanagerConfigs doesn't hold an unique identifier so we use the config hash as the identifier. b, err := json.Marshal(v) if err != nil { return err } c[fmt.Sprintf("%x", md5.Sum(b))] = v.ServiceDiscoveryConfig } return discoveryManagerNotify.ApplyConfig(c) }, //从配置文件中提取Section:rule_files func(cfg *config.Config) error { // Get all rule files matching the configuration paths. var files []string for _, pat := range cfg.RuleFiles { fs, err := filepath.Glob(pat) if err != nil { // The only error can be a bad pattern. return fmt.Errorf("error retrieving rule files for %s: %s", pat, err) } files = append(files, fs...) } return ruleManager.Update(time.Duration(cfg.GlobalConfig.EvaluationInterval), files) }, }(2) 其中，服务组件remoteStorage，webHandler，notifierManager和ScrapeManager的ApplyConfig方法，参数cfg *config.Config中传递的配置文件，是整个文件prometheus.yml，点击prometheus.yml查看一个完整的配置文件示例
prometheus/scrape/manager.go func (m *Manager) ApplyConfig(cfg *config.Config) error { ....... }(3) 而服务组件discoveryManagerScrape和discoveryManagerNotify的Appliconfig方法，参数中传递的配置文件，是文件中的一个Section
prometheus/discovery/manager.go func (m *Manager) ApplyConfig(cfg map[string]sd_config.ServiceDiscoveryConfig) error { ...... }所以，需要利用匿名函数提前处理下，取出对应的Section
prometheus/cmd/prometheus/main.go //从配置文件中提取Section:scrape_configs func(cfg *config.Config) error { c := make(map[string]sd_config.ServiceDiscoveryConfig) for _, v := range cfg.ScrapeConfigs { c[v.JobName] = v.ServiceDiscoveryConfig } return discoveryManagerScrape.ApplyConfig(c) }, //从配置文件中提取Section:alerting func(cfg *config.Config) error { c := make(map[string]sd_config.ServiceDiscoveryConfig) for _, v := range cfg.AlertingConfig.AlertmanagerConfigs { // AlertmanagerConfigs doesn't hold an unique identifier so we use the config hash as the identifier. b, err := json.Marshal(v) if err != nil { return err } c[fmt.Sprintf("%x", md5.Sum(b))] = v.ServiceDiscoveryConfig } return discoveryManagerNotify.ApplyConfig(c) },(4) 服务组件ruleManager，在匿名函数中提取出Section:rule_files
prometheus/cmd/prometheus/main.go //从配置文件中提取Section:rule_files func(cfg *config.Config) error { // Get all rule files matching the configuration paths. var files []string for _, pat := range cfg.RuleFiles { fs, err := filepath.Glob(pat) if err != nil { // The only error can be a bad pattern. return fmt.Errorf("error retrieving rule files for %s: %s", pat, err) } files = append(files, fs...) } return ruleManager.Update(time.Duration(cfg.GlobalConfig.EvaluationInterval), files) },利用该组件内置的Update方法完成配置管理
prometheus/rules/manager.go func (m *Manager) Update(interval time.Duration, files []string) error { ....... }(5) 最后，通过reloadConfig方法，加载各个服务组件的配置项
prometheus/cmd/prometheus/main.go func reloadConfig(filename string, logger log.Logger, rls ...func(*config.Config) error) (err error) { level.Info(logger).Log("msg", "Loading configuration file", "filename", filename) defer func() { if err == nil { configSuccess.Set(1) configSuccessTime.SetToCurrentTime() } else { configSuccess.Set(0) } }() conf, err := config.LoadFile(filename) if err != nil { return fmt.Errorf("couldn't load configuration (--config.file=%q): %v", filename, err) } failed := false //通过一个for循环，加载各个服务组件的配置项 for _, rl := range rls { if err := rl(conf); err != nil { level.Error(logger).Log("msg", "Failed to apply configuration", "err", err) failed = true } } if failed { return fmt.Errorf("one or more errors occurred while applying the new configuration (--config.file=%q)", filename) } promql.SetDefaultEvaluationInterval(time.Duration(conf.GlobalConfig.EvaluationInterval)) level.Info(logger).Log("msg", "Completed loading of configuration file", "filename", filename) return nil }(1) 这里引用了github.com/oklog/oklog/pkg/group包，实例化一个对象g
prometheus/cmd/prometheus/main.go // "github.com/oklog/oklog/pkg/group" var g group.Group { ...... }对象g中包含各个服务组件的入口，通过调用Add方法把把这些入口添加到对象g中，以组件scrapeManager为例：
prometheus/cmd/prometheus/main.go { // Scrape manager. //通过方法Add，把ScrapeManager组件添加到g中 g.Add( func() error { // When the scrape manager receives a new targets list // it needs to read a valid config for each job. // It depends on the config being in sync with the discovery manager so // we wait until the config is fully loaded. <-reloadReady.C //ScrapeManager组件的启动函数 err := scrapeManager.Run(discoveryManagerScrape.SyncCh()) level.Info(logger).Log("msg", "Scrape manager stopped") return err }, func(err error) { // Scrape manager needs to be stopped before closing the local TSDB // so that it doesn't try to write samples to a closed storage. level.Info(logger).Log("msg", "Stopping scrape manager...") scrapeManager.Stop() }, ) }(2) 通过对象g，调用方法run，启动所有服务组件
prometheus/cmd/prometheus/main.go if err := g.Run(); err != nil { level.Error(logger).Log("err", err) os.Exit(1) } level.Info(logger).Log("msg", "See you next time!")