Docker Swarm代码分析笔记（2）——discovery

Docker的discovery package提供了实现新的backend定义的interface（discovey.go）：

package discovery

import (
    "errors"
    "time"
)

var (
    // ErrNotSupported is returned when a discovery service is not supported.
    ErrNotSupported = errors.New("discovery service not supported")

    // ErrNotImplemented is returned when discovery feature is not implemented
    // by discovery backend.
    ErrNotImplemented = errors.New("not implemented in this discovery service")
)

// Watcher provides watching over a cluster for nodes joining and leaving.
type Watcher interface {
    // Watch the discovery for entry changes.
    // Returns a channel that will receive changes or an error.
    // Providing a non-nil stopCh can be used to stop watching.
    Watch(stopCh <-chan struct{}) (<-chan Entries, <-chan error)
}

// Backend is implemented by discovery backends which manage cluster entries.
type Backend interface {
    // Watcher must be provided by every backend.
    Watcher

    // Initialize the discovery with URIs, a heartbeat, a ttl and optional settings.
    Initialize(string, time.Duration, time.Duration, map[string]string) error

    // Register to the discovery.
    Register(string) error
}

Watcher interface用于node加入或移除出cluster时的回调函数。Initialize用于backend的初始化，而Register用于将node加入cluster。