Prometheus源码系列：服务发现 (serviceDiscover)

•  服务发现 (serviceDiscover) 简介

　　Prometheus采用pull方式拉取监控数据，需要实时感知被监控服务(Target)的变化．服务发现(serviceDiscover)支持多种服务发现系统，这些系统可以动态感知被监控的服务(Target)的变化，把变化的被监控服务(Target)转换为targetgroup.Group的结构，通过管道up发送个服务发现(serviceDiscover)．以版本 v2.7.1为例，目前服务发现(serviceDiscover)支持的服务发现系统类型如下：

// ServiceDiscoveryConfig configures lists of different service discovery mechanisms.
type ServiceDiscoveryConfig struct {
	// List of labeled target groups for this job.
	StaticConfigs []*targetgroup.Group `yaml:"static_configs,omitempty"`
	// List of DNS service discovery configurations.
	DNSSDConfigs []*dns.SDConfig `yaml:"dns_sd_configs,omitempty"`
	// List of file service discovery configurations.
	FileSDConfigs []*file.SDConfig `yaml:"file_sd_configs,omitempty"`
	// List of Consul service discovery configurations.
	ConsulSDConfigs []*consul.SDConfig `yaml:"consul_sd_configs,omitempty"`
	// List of Serverset service discovery configurations.
	ServersetSDConfigs []*zookeeper.ServersetSDConfig `yaml:"serverset_sd_configs,omitempty"`
	// NerveSDConfigs is a list of Nerve service discovery configurations.
	NerveSDConfigs []*zookeeper.NerveSDConfig `yaml:"nerve_sd_configs,omitempty"`
	// MarathonSDConfigs is a list of Marathon service discovery configurations.
	MarathonSDConfigs []*marathon.SDConfig `yaml:"marathon_sd_configs,omitempty"`
	// List of Kubernetes service discovery configurations.
	KubernetesSDConfigs []*kubernetes.SDConfig `yaml:"kubernetes_sd_configs,omitempty"`
	// List of GCE service discovery configurations.
	GCESDConfigs []*gce.SDConfig `yaml:"gce_sd_configs,omitempty"`
	// List of EC2 service discovery configurations.
	EC2SDConfigs []*ec2.SDConfig `yaml:"ec2_sd_configs,omitempty"`
	// List of OpenStack service discovery configurations.
	OpenstackSDConfigs []*openstack.SDConfig `yaml:"openstack_sd_configs,omitempty"`
	// List of Azure service discovery configurations.
	AzureSDConfigs []*azure.SDConfig `yaml:"azure_sd_configs,omitempty"`
	// List of Triton service discovery configurations.
	TritonSDConfigs []*triton.SDConfig `yaml:"triton_sd_configs,omitempty"`
}

•  服务发现 (serviceDiscover) 管理多种服务发现系统

　　服务发现(serviceDiscover)为了实现对以上服务发现系统的统一管理，提供了一个Discoverer接口，由各个服务发现系统来实现，然后把上线的服务(Target)通过up管道发送给服务发现(serviceDiscover)

prometheus/discovery/manager.go

type Discoverer interface {
	// Run hands a channel to the discovery provider (Consul, DNS etc) through which it can send
	// updated target groups.
	// Must returns if the context gets canceled. It should not close the update
	// channel on returning.
	Run(ctx context.Context, up chan<- []*targetgroup.Group)
}


prometheus/discovery/targetgroup/targetgroup.go

// Group is a set of targets with a common label set(production , test, staging etc.).
type Group struct {
	// Targets is a list of targets identified by a label set. Each target is
	// uniquely identifiable in the group by its address label.
	Targets []model.LabelSet //服务(Target)主要标签，比如ip + port，示例："__address__": "localhost:9100"
	// Labels is a set of labels that is common across all targets in the group.
	Labels model.LabelSet　//服务(Target)其他标签，可以为空：

	// Source is an identifier that describes a group of targets.
	Source string //全局唯一个ID，示例：Source: "0"
}

Group的一个示例：
(dlv) p tg
*github.com/prometheus/prometheus/discovery/targetgroup.Group {
	Targets: []github.com/prometheus/common/model.LabelSet len: 1, cap: 1, [
	　　　　　　　[
		　　　　　　　"__address__": "localhost:9100", 
	　　　　　　　],
　　　　　　　　]
	],
	Labels: github.com/prometheus/common/model.LabelSet nil,
	Source: "0",}

　　除了静态服务发现系统(StaticConfigs)在prometheus/discovery/manager.go中实现了以上接口，其他动态服务发现系统，在prometheus/discovery/下都在有各自的目录下实现．

• 服务发现 (serviceDiscover)的配置初始化及应用

１． 配置文件初始化