【云原生 • Prometheus】Prometheus 注册中心Eureka服务发现原理

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Prometheus 注册中心Eureka服务发现原理

概述

Eureka服务发现协议允许使用Eureka Rest API检索出Prometheus需要监控的targets，Prometheus会定时周期性的从Eureka调用Eureka Rest API，并将每个应用实例创建出一个target。

Eureka服务发现协议支持对如下元标签进行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_<metadataname>: app instance metadata
  • __meta_eureka_app_instance_datacenterinfo_name: the datacenter name of the app instance
  • __meta_eureka_app_instance_datacenterinfo_<metadataname>: the datacenter metadata

eureka_sd_configs常见配置如下：

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- job_name: 'eureka'
  eureka_sd_configs:
    - server: http://localhost:8761/eureka #eureka server地址
      refresh_interval: 1m #刷新间隔，默认30s

eureka_sd_configs官网支持主要配置如下：

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server: <string>

basic_auth:

[ username: <string> ]

[ password: <secret> ]

[ password_file: <string> ]


Configures the scrape request's TLS settings.


tls_config:

[ <tls_config> ]


Optional proxy URL.


[ proxy_url: <string> ]


Configure whether HTTP requests follow HTTP 3xx redirects.


[ follow_redirects: <bool> | default = true ]


Refresh interval to re-read the app instance list.


[ refresh_interval: <duration> | default = 30s ]

Eureka协议实现

基于Eureka服务发现协议核心逻辑都封装在discovery/eureka.go的func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error)方法中：

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func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {

// 通过Eureka REST API接口从eureka拉取元数据：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 {//遍历app

// targetsForApp()方法将app下每个instance部分转成target

targets := targetsForApp(&app)

//解析的采集点合入一起

tg.Targets = append(tg.Targets, targets...)

}

return []*targetgroup.Group{tg}, nil

}

refresh方法主要有两个流程：

1、fetchApps()：从eureka-server的/eureka/apps接口拉取注册服务信息；

2、targetsForApp()：遍历app下instance，将每个instance解析出一个target，并添加一堆元标签数据。

如下示例从eureka-server的/eureka/apps接口拉取的注册服务信息：

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<applications>

<versions__delta>1</versions__delta>

<apps__hashcode>UP_1</apps__hashcode>

<application>

<name>SERVICE-PROVIDER-01</name>

<instance>

<instanceId>localhost:service-provider-01:8001</instanceId>

<hostName>192.168.3.121</hostName>

<app>SERVICE-PROVIDER-01</app>

<ipAddr>192.168.3.121</ipAddr>

<status>UP</status>

<overriddenstatus>UNKNOWN</overriddenstatus>

<port enabled="true">8001</port>

<securePort enabled="false">443</securePort>

<countryId>1</countryId>

<dataCenterInfo class="com.netflix.appinfo.InstanceInfo$DefaultDataCenterInfo">

<name>MyOwn</name>

</dataCenterInfo>

<leaseInfo>

<renewalIntervalInSecs>30</renewalIntervalInSecs>

<durationInSecs>90</durationInSecs>

<registrationTimestamp>1629385562130</registrationTimestamp>

<lastRenewalTimestamp>1629385682050</lastRenewalTimestamp>

<evictionTimestamp>0</evictionTimestamp>

<serviceUpTimestamp>1629385562132</serviceUpTimestamp>

</leaseInfo>

<metadata>

<management.port>8001</management.port>

<scrape__enable>true</scrape__enable>

<scrape.port>8080</scrape.port>

</metadata>

<homePageUrl>http://192.168.3.121/</homePageUrl>

<statusPageUrl>http://192.168.3.121/actuator/info</statusPageUrl>

<healthCheckUrl>http://192.168.3.121/actuator/health</healthCheckUrl>

<vipAddress>service-provider-01</vipAddress>

<secureVipAddress>service-provider-01</secureVipAddress>

<isCoordinatingDiscoveryServer>false</isCoordinatingDiscoveryServer>

<lastUpdatedTimestamp>1629385562132</lastUpdatedTimestamp>

<lastDirtyTimestamp>1629385562039</lastDirtyTimestamp>

<actionType>ADDED</actionType>

</instance>

</application>

</applications>

instance信息会被解析成采集点target：

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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，没有port则默认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，其它非法字符都会被替换成下划线_

ln := strutil.SanitizeLabelName(m.XMLName.Local)

target[model.LabelName(appInstanceMetadataPrefix+ln)] = lv(m.Content)

}

}


targets = append(targets, target)


}

return targets

}

解析比较简单，就不再分析，解析后的标签数据如下图：

标签中有两个特别说明下：

1、address：这个取值instance.hostname和port(默认80)，所以要注意注册到eureka上的hostname准确性，不然可能无法抓取；

2、metadata-map数据会被转成meta_eureka_app_instance_metadata<metadataname>格式标签，prometheus进行relabeling 一般操作metadata-map，可以自定义metric_path、抓取端口等；

3、prometheus的label只支持[a-zA-Z0-9]，其它非法字符都会被转换成下划线，具体参加：strutil.SanitizeLabelName(m.XMLName.Local)；但是eureka的metadata-map标签含有下划线时，注册到eureka-server上变成双下划线，如下配置:

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eureka:

instance:

metadata-map:

scrape_enable: true

scrape.port: 8080

通过/eureka/apps获取如下：

总结

基于Eureka服务发现原理如下图：

基于eureka_sd_configs服务发现协议配置创建Discoverer，并通过协程运行Discoverer.Run方法，Eureka服务发现核心逻辑封装discovery/eureka.go的func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error)方法中。

refresh方法中主要调用两个方法：

1、fetchApps：定时周期从Eureka Server的/eureka/apps接口拉取注册上来的服务元数据信息；

2、targetsForApp：解析上步骤拉取的元数据信息，遍历app下的instance，将每个instance解析成target，并将其它元数据信息转换成target元标签可以用于relabel_configs操作

#prometheus#服务#数据#协议#原理