注册中心

Dubbogo 为注册中心抽象了一套接口如下：

  1. // Registry Extension - Registry
  2. type Registry interface {
  3.     common.Node
  5.     // Register is used for service provider calling, register services
  6.     // to registry. And it is also used for service consumer calling, register
  7.     // services cared about, for dubbo's admin monitoring.
  8.     Register(url *common.URL) error
  10.     // UnRegister is required to support the contract:
  11.     // 1. If it is the persistent stored data of dynamic=false, the
  12.     //    registration data can not be found, then the IllegalStateException
  13.     //    is thrown, otherwise it is ignored.
  14.     // 2. Unregister according to the full url match.
  15.     // url Registration information, is not allowed to be empty, e.g:
  16.     // dubbo://10.20.153.10/org.apache.dubbo.foo.BarService?version=1.0.0&application=kylin
  17.     UnRegister(url *common.URL) error
  19.     // Subscribe is required to support the contract:
  20.     // When creating new registry extension, pls select one of the
  21.     // following modes.
  22.     // Will remove in dubbogo version v1.1.0
  23.     // mode1: return Listener with Next function which can return
  24.     //        subscribe service event from registry
  25.     // Deprecated!
  26.     // subscribe(event.URL) (Listener, error)
  27.     // Will replace mode1 in dubbogo version v1.1.0
  28.     // mode2: callback mode, subscribe with notify(notify listener).
  29.     Subscribe(*common.URL, NotifyListener) error
  31.     // UnSubscribe is required to support the contract:
  32.     // 1. If don't subscribe, ignore it directly.
  33.     // 2. Unsubscribe by full URL match.
  34.     // url Subscription condition, not allowed to be empty, e.g.
  35.     // consumer://10.20.153.10/org.apache.dubbo.foo.BarService?version=1.0.0&application=kylin
  36.     // listener A listener of the change event, not allowed to be empty
  37.     UnSubscribe(*common.URL, NotifyListener) error
  38. }

该接口主要包含四个方法，分别是注册、反注册、订阅、取消订阅。顾名思义，概括了客户端和服务端与注册中心交互的动作。针对普通接口级服务注册发现场景，在Provider 服务启动时，会将自身服务接口信息抽象为一个 url，该 url 包含了客户端发起调用所需的所有信息（ip、端口、协议等），服务端的注册中心组件会将该 url 写入注册中心（例如zk）。客户端启动后，在服务引用 Refer 步骤会通过注册中心组件订阅（Subscribe）需要的服务信息，获取到的服务信息以异步事件更新的形式写入客户端缓存，从而在服务发现成功后，可以根据拿到的服务 url 参数，向对应服务提供者发起调用。

最后修改 December 16, 2022: Fix check (#1736) (97972c1)