Zookeeper

Basic usage and working principle of Zookeeper metadata center

1 Preparation

2 Instructions

2.1 Adding Maven Dependency

If the project has already enabled Zookeeper as the registry center, no additional configuration is needed.

If Zookeeper is not used as the registry center, please refer to Add Zookeeper-related dependencies for the registry center.

2.2 Enable Zookeeper Configuration Center

  1. <dubbo:metadata-report address="zookeeper://127.0.0.1:2181"/>

or

  1. dubbo
  2.   metadata-report
  3.     address: zookeeper://127.0.0.1:2181

or

  1. dubbo.metadata-report.address=zookeeper://127.0.0.1:2181

or

  1. MetadataReportConfig metadataConfig = new MetadataReportConfig();
  2. metadataConfig.setAddress("zookeeper://127.0.0.1:2181");

For the format of address, please refer to zookeeper register center - Enable Configuration

3 Advanced Configuration

For complete configuration parameters, please refer to metadata-report-config.

4 Working Principle

4.1 Service Operation Metadata

Zookeeper stores data based on a tree structure, and its metadata information is located at the following nodes:

  1. Provider: /dubbo/metadata/{interface name}/{version}/{group}/provider/{application name}
  2. Consumer: /dubbo/metadata/{interface name}/{version}/{group}/consumer/{application name}

When version or group does not exist, the version path and group path will be removed, paths are as follows:

  1. Provider: /dubbo/metadata/{interface name}/provider/{application name}
  2. Consumer: /dubbo/metadata/{interface name}/consumer/{application name}

Use zkCli get command to view data.

Provider node:

  1. [zk: localhost:2181(CONNECTED) 8] get /dubbo/metadata/org.apache.dubbo.demo.DemoService/provider/demo-provider
  2. {"parameters":{"side":"provider","interface":"org.apache.dubbo.demo.DemoService","metadata-type":"remote","application":"demo-provider","dubbo":"2.0.2","release":"","anyhost":"true","delay":"5000","methods":"sayHello,sayHelloAsync","deprecated":"false","dynamic":"true","timeout":"3000","generic":"false"},"canonicalName":"org.apache.dubbo.demo.DemoService","codeSource":"file:/Users/apple/IdeaProjects/dubbo/dubbo-demo/dubbo-demo-interface/target/classes/","methods":[{"name":"sayHelloAsync","parameterTypes":["java.lang.String"],"returnType":"java.util.concurrent.CompletableFuture"},{"name":"sayHello","parameterTypes":["java.lang.String"],"returnType":"java.lang.String"}],"types":[{"type":"java.util.concurrent.CompletableFuture","properties":{"result":"java.lang.Object","stack":"java.util.concurrent.CompletableFuture.Completion"}},{"type":"java.lang.Object"},{"type":"java.lang.String"},{"type":"java.util.concurrent.CompletableFuture.Completion","properties":{"next":"java.util.concurrent.CompletableFuture.Completion","status":"int"}},{"type":"int"}]}
  3. cZxid = 0x25a9b1
  4. ctime = Mon Jun 28 21:35:17 CST 2021
  5. mZxid = 0x25a9b1
  6. mtime = Mon Jun 28 21:35:17 CST 2021
  7. pZxid = 0x25a9b1
  8. cversion = 0
  9. dataVersion = 0
  10. aclVersion = 0
  11. ephemeralOwner = 0x0
  12. dataLength = 1061
  13. numChildren = 0

Consumer node:

  1. [zk: localhost:2181(CONNECTED) 10] get /dubbo/metadata/org.apache.dubbo.demo.DemoService/consumer/demo-consumer
  2. {"side":"consumer","interface":"org.apache.dubbo.demo.DemoService","metadata-type":"remote","application":"demo-consumer","dubbo":"2.0.2","release":"","sticky":"false","check":"false","methods":"sayHello,sayHelloAsync"}
  3. cZxid = 0x25aa24
  4. ctime = Mon Jun 28 21:57:43 CST 2021
  5. mZxid = 0x25aa24
  6. mtime = Mon Jun 28 21:57:43 CST 2021
  7. pZxid = 0x25aa24
  8. cversion = 0
  9. dataVersion = 0
  10. aclVersion = 0
  11. ephemeralOwner = 0x0
  12. dataLength = 219
  13. numChildren = 0

4.2 Address Discovery - Interface-Application Name Mapping

In Dubbo 3.0, the service introspection mechanism is used by default to achieve service discovery. For service introspection, you can refer to Service Introspection

In short, the service introspection mechanism needs to find the corresponding application name through the interface name. This relationship can be one-to-many, meaning a service name may correspond to multiple different application names. In 3.0, the metadata center provides this mapping capability.

Zookeeper

As mentioned above, service name and application name may be one-to-many. In Zookeeper, a single key-value pair is used for storage, with multiple application names separated by commas ,. Since it is a single key-value for data storage, there may be concurrent overwrite issues in a multi-client scenario. Therefore, we use Zookeeper’s version mechanism to address this issue. In Zookeeper, each modification to data increases the dataVersion, allowing the use of the version mechanism to resolve concurrent issues during updates by multiple clients. Different clients check the version before updating, treating it as a local credential. During the update, the version credential is sent to the server for comparison. If they do not match, it indicates modification by another client, and the credential should be re-obtained for retry (CAS). Currently, if 6 retries fail, the update mapping action is abandoned.

Curator api.

  1. CuratorFramework client = ...
  2. client.setData().withVersion(ticket).forPath(path, dataBytes);

Mapping information is located at:

  1. /dubbo/mapping/{service name}

Use zkCli get command to view data.

  1. [zk: localhost:2181(CONNECTED) 26] get /dubbo/mapping/org.apache.dubbo.demo.DemoService
  2. demo-provider,two-demo-provider,dubbo-demo-annotation-provider
  3. cZxid = 0x25a80f
  4. ctime = Thu Jun 10 01:36:40 CST 2021
  5. mZxid = 0x25a918
  6. mtime = Fri Jun 11 18:46:40 CST 2021
  7. pZxid = 0x25a80f
  8. cversion = 0
  9. dataVersion = 2
  10. aclVersion = 0
  11. ephemeralOwner = 0x0
  12. dataLength = 62
  13. numChildren = 0

4.3 Address Discovery - Interface Configuration Metadata

To enable remote interface configuration metadata registration, the following configuration must be added to the application, as by default Dubbo3 application-level service discovery will enable service introspection mode and will not register data to the metadata center.

  1.  dubbo.application.metadata-type=remote

Or to enable centralized metadata registration while in introspection mode

  1. dubbo.application.metadata-type=local
  2. dubbo.metadata-report.report-metadata=true

The application-level metadata in Zookeeper is located at /dubbo/metadata/{application name}/{revision}

  1. [zk: localhost:2181(CONNECTED) 33] get /dubbo/metadata/demo-provider/da3be833baa2088c5f6776fb7ab1a436
  2. {"app":"demo-provider","revision":"da3be833baa2088c5f6776fb7ab1a436","services":{"org.apache.dubbo.demo.DemoService:dubbo":{"name":"org.apache.dubbo.demo.DemoService","protocol":"dubbo","path":"org.apache.dubbo.demo.DemoService","params":{"side":"provider","release":"","methods":"sayHello,sayHelloAsync","deprecated":"false","dubbo":"2.0.2","pid":"38298","interface":"org.apache.dubbo.demo.DemoService","service-name-mapping":"true","timeout":"3000","generic":"false","metadata-type":"remote","delay":"5000","application":"demo-provider","dynamic":"true","REGISTRY_CLUSTER":"registry1","anyhost":"true","timestamp":"1626887121829"}},"org.apache.dubbo.demo.RestDemoService:1.0.0:rest":{"name":"org.apache.dubbo.demo.RestDemoService","version":"1.0.0","protocol":"rest","path":"org.apache.dubbo.demo.RestDemoService","params":{"side":"provider","release":"","methods":"getRemoteApplicationName,sayHello,hello,error","deprecated":"false","dubbo":"2.0.2","pid":"38298","interface":"org.apache.dubbo.demo.RestDemoService","service-name-mapping":"true","version":"1.0.0","timeout":"5000","generic":"false","revision":"1.0.0","metadata-type":"remote","delay":"5000","application":"demo-provider","dynamic":"true","REGISTRY_CLUSTER":"registry1","anyhost":"true","timestamp":"1626887120943"}}}}
  3. cZxid = 0x25b336
  4. ctime = Thu Jul 22 01:05:55 CST 2021
  5. mZxid = 0x25b336
  6. mtime = Thu Jul 22 01:05:55 CST 2021
  7. pZxid = 0x25b336
  8. cversion = 0
  9. dataVersion = 0
  10. aclVersion = 0
  11. ephemeralOwner = 0x0
  12. dataLength = 1286
  13. numChildren = 0

Feedback

Was this page helpful?

Yes No

Last modified September 30, 2024: Update & Translate Overview Docs (#3040) (d37ebceaea7)