Prometheus 注冊中心Eureka服務發(fā)現(xiàn)原理
概述
Eureka服務發(fā)現(xiàn)協(xié)議允許使用Eureka Rest API檢索出Prometheus需要監(jiān)控的targets，Prometheus會定時周期性的從Eureka調用Eureka Rest API，并將每個應用實例創(chuàng)建出一個target。
(資料圖片)
Eureka服務發(fā)現(xiàn)協(xié)議支持對如下元標簽進行relabeling：
__meta_eureka_app_name: the name of the app__meta_eureka_app_instance_id: the ID of the app instance__meta_eureka_app_instance_hostname: the hostname of the instance__meta_eureka_app_instance_homepage_url: the homepage url of the app instance__meta_eureka_app_instance_statuspage_url: the status page url of the app instance__meta_eureka_app_instance_healthcheck_url: the health check url of the app instance__meta_eureka_app_instance_ip_addr: the IP address of the app instance__meta_eureka_app_instance_vip_address: the VIP address of the app instance__meta_eureka_app_instance_secure_vip_address: the secure VIP address of the app instance__meta_eureka_app_instance_status: the status of the app instance__meta_eureka_app_instance_port: the port of the app instance__meta_eureka_app_instance_port_enabled: the port enabled of the app instance__meta_eureka_app_instance_secure_port: the secure port address of the app instance__meta_eureka_app_instance_secure_port_enabled: the secure port of the app instance__meta_eureka_app_instance_country_id: the country ID of the app instance__meta_eureka_app_instance_metadata_: app instance metadata__meta_eureka_app_instance_datacenterinfo_name: the datacenter name of the app instance__meta_eureka_app_instance_datacenterinfo_: the datacenter metadataeureka_sd_configs常見配置如下：
- job_name: "eureka" eureka_sd_configs: - server: http://localhost:8761/eureka #eureka server地址 refresh_interval: 1m #刷新間隔，默認30seureka_sd_configs官網(wǎng)支持主要配置如下：
server: basic_auth: [ username: ] [ password: ] [ password_file: ]# Configures the scrape request"s TLS settings.tls_config: [ ]# Optional proxy URL.[ proxy_url: ]# Configure whether HTTP requests follow HTTP 3xx redirects.[ follow_redirects: | default = true ]# Refresh interval to re-read the app instance list.[ refresh_interval: | default = 30s ] Eureka協(xié)議實現(xiàn)
基于Eureka服務發(fā)現(xiàn)協(xié)議核心邏輯都封裝在discovery/eureka.go的func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error)方法中：
func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) { // 通過Eureka REST API接口從eureka拉取元數(shù)據(jù)：http://ip:port/eureka/apps apps, err := fetchApps(ctx, d.server, d.client) if err != nil { return nil, err } tg := &targetgroup.Group{ Source: "eureka", } for _, app := range apps.Applications {//遍歷app // targetsForApp()方法將app下每個instance部分轉成target targets := targetsForApp(&app) //解析的采集點合入一起 tg.Targets = append(tg.Targets, targets...) } return []*targetgroup.Group{tg}, nil}refresh方法主要有兩個流程：
1、fetchApps()：從eureka-server的/eureka/apps接口拉取注冊服務信息；
2、targetsForApp()：遍歷app下instance，將每個instance解析出一個target，并添加一堆元標簽數(shù)據(jù)。
如下示例從eureka-server的/eureka/apps接口拉取的注冊服務信息：
1 UP_1_ SERVICE-PROVIDER-01 localhost:service-provider-01:8001 192.168.3.121 SERVICE-PROVIDER-01 192.168.3.121 UP UNKNOWN 8001 443 1 MyOwn 30 90 1629385562130 1629385682050 0 1629385562132 8001 true 8080 http://192.168.3.121:8001/ http://192.168.3.121:8001/actuator/info http://192.168.3.121:8001/actuator/health service-provider-01 service-provider-01 false 1629385562132 1629385562039 ADDED instance信息會被解析成采集點target：
func targetsForApp(app *Application) []model.LabelSet { targets := make([]model.LabelSet, 0, len(app.Instances)) // Gather info about the app"s "instances". Each instance is considered a task. for _, t := range app.Instances { var targetAddress string // __address__取值方式：instance.hostname和port，沒有port則默認port=80 if t.Port != nil { targetAddress = net.JoinHostPort(t.HostName, strconv.Itoa(t.Port.Port)) } else { targetAddress = net.JoinHostPort(t.HostName, "80") } target := model.LabelSet{ model.AddressLabel: lv(targetAddress), model.InstanceLabel: lv(t.InstanceID), appNameLabel: lv(app.Name), appInstanceHostNameLabel: lv(t.HostName), appInstanceHomePageURLLabel: lv(t.HomePageURL), appInstanceStatusPageURLLabel: lv(t.StatusPageURL), appInstanceHealthCheckURLLabel: lv(t.HealthCheckURL), appInstanceIPAddrLabel: lv(t.IPAddr), appInstanceVipAddressLabel: lv(t.VipAddress), appInstanceSecureVipAddressLabel: lv(t.SecureVipAddress), appInstanceStatusLabel: lv(t.Status), appInstanceCountryIDLabel: lv(strconv.Itoa(t.CountryID)), appInstanceIDLabel: lv(t.InstanceID), } if t.Port != nil { target[appInstancePortLabel] = lv(strconv.Itoa(t.Port.Port)) target[appInstancePortEnabledLabel] = lv(strconv.FormatBool(t.Port.Enabled)) } if t.SecurePort != nil { target[appInstanceSecurePortLabel] = lv(strconv.Itoa(t.SecurePort.Port)) target[appInstanceSecurePortEnabledLabel] = lv(strconv.FormatBool(t.SecurePort.Enabled)) } if t.DataCenterInfo != nil { target[appInstanceDataCenterInfoNameLabel] = lv(t.DataCenterInfo.Name) if t.DataCenterInfo.Metadata != nil { for _, m := range t.DataCenterInfo.Metadata.Items { ln := strutil.SanitizeLabelName(m.XMLName.Local) target[model.LabelName(appInstanceDataCenterInfoMetadataPrefix+ln)] = lv(m.Content) } } } if t.Metadata != nil { for _, m := range t.Metadata.Items { // prometheus label只支持[^a-zA-Z0-9_]字符，其它非法字符都會被替換成下劃線_ ln := strutil.SanitizeLabelName(m.XMLName.Local) target[model.LabelName(appInstanceMetadataPrefix+ln)] = lv(m.Content) } } targets = append(targets, target) } return targets}解析比較簡單，就不再分析，解析后的標簽數(shù)據(jù)如下圖：
標簽中有兩個特別說明下：
1、__address__：這個取值instance.hostname和port(默認80)，所以要注意注冊到eureka上的hostname準確性，不然可能無法抓??；
2、metadata-map數(shù)據(jù)會被轉成__meta_eureka_app_instance_metadata_格式標簽，prometheus進行relabeling一般操作metadata-map，可以自定義metric_path、抓取端口等；
3、prometheus的label只支持[a-zA-Z0-9_]，其它非法字符都會被轉換成下劃線，具體參加：strutil.SanitizeLabelName(m.XMLName.Local)；但是eureka的metadata-map標簽含有下劃線時，注冊到eureka-server上變成雙下劃線，如下配置:
eureka: instance: metadata-map: scrape_enable: true scrape.port: 8080通過/eureka/apps獲取如下：
總結
基于Eureka服務發(fā)現(xiàn)原理如下圖：
基于eureka_sd_configs服務發(fā)現(xiàn)協(xié)議配置創(chuàng)建Discoverer，并通過協(xié)程運行Discoverer.Run方法，Eureka服務發(fā)現(xiàn)核心邏輯封裝discovery/eureka.go的func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error)方法中。
refresh方法中主要調用兩個方法：
1、fetchApps：定時周期從Eureka Server的/eureka/apps接口拉取注冊上來的服務元數(shù)據(jù)信息；
2、targetsForApp：解析上步驟拉取的元數(shù)據(jù)信息，遍歷app下的instance，將每個instance解析成target，并將其它元數(shù)據(jù)信息轉換成target元標簽可以用于relabel_configs操作
關鍵詞：