Zookeeper

1 precondition

• Understand Dubbo basic development steps
• Install and start Zookeeper

2 Instructions for use

Check out full sample code here

2.1 Add Maven dependency

<properties>
    <dubbo.version>3.0.8</dubbo.version>
</properties>

<dependencies>
    <dependency>
        <groupId>org.apache.dubbo</groupId>
        <artifactId>dubbo</artifactId>
        <version>${dubbo.version}</version>
    </dependency>
    <!-- This dependency helps to introduce Curator and Zookeeper dependencies that are necessary for Dubbo to work with zookeeper as transitive dependencies -->
    <dependency>
        <groupId>org.apache.dubbo</groupId>
        <artifactId>dubbo-dependencies-zookeeper</artifactId>
        <version>${dubbo.version}</version>
        <type>pom</type>
    </dependency>
</dependencies>

dubbo-dependencies-zookeeper will automatically add Zookeeper-related client dependencies to the application, reducing the cost of using Zookeeper for users. If there is a version compatibility problem during use, users can also add it by themselves instead of using dubbo-dependencies-zookeeper Curator, Zookeeper Client and other dependencies.

Since Dubbo uses Curator as a programming client interacting with Zookeeper Server, special attention should be paid to the compatibility between Zookeeper Server and Dubbo version dependencies

2.2 Configure and enable Zookeeper

# application.yml
dubbo
 registry
   address: zookeeper://localhost:2181

or

# dubbo.properties
dubbo.registry.address=zookeeper://localhost:2181

or

<dubbo:registry address="zookeeper://localhost:2181" />

address is the only attribute that must be specified to enable the zookeeper registration center, and in a production environment, address is usually specified as the cluster address, such as

address=zookeeper://10.20.153.10:2181?backup=10.20.153.11:2181,10.20.153.12:2181

It is also possible to configure protocol and address separately, such as

<dubbo:registry protocol="zookeeper" address="10.20.153.10:2181,10.20.153.11:2181,10.20.153.12:2181" />

3 Advanced configuration

3.1 Authentication and Authorization

If Zookeeper enables authentication, Dubbo supports passing in the identity by specifying username and password.

# application.yml
dubbo
 registry
   address: zookeeper://localhost:2181
   username: hello
   password: 1234

You can also directly expand the parameters on the address address=zookeeper://hello:1234@localhost:2181

3.2 Group isolation

By specifying the group attribute, the logical isolation of microservice addresses can be achieved within the same Zookeeper cluster. For example, multiple sets of development environments can be isolated in one cluster, and isolation can be achieved at the address discovery level.

# application.yml
dubbo
 registry
   address: zookeeper://localhost:2181
   group: daily1

3.3 Other extended configurations

Configure connection and session expiration time

# application.yml
dubbo
 registry
   address: zookeeper://localhost:2181
   timeout: 30 * 1000* # Connection timeout, default 30s
   session: 60 * 1000* # Session timeout, default 60s

The Zookeeper registry also supports some other control parameters, for details, see Registry configuration item manual

4 How it works

4.1 Dubbo2 node structure

process:

• When the service provider starts: write its own URL address to the /dubbo/com.foo.BarService/providers directory.
• When the service consumer starts: subscribe to the provider URL address under the /dubbo/com.foo.BarService/providers directory. And write your own URL address to /dubbo/com.foo.BarService/consumers directory
• When monitoring center starts: subscribe to all provider and consumer URL addresses under /dubbo/com.foo.BarService directory.

The following functions are supported:

• When the provider has abnormal downtime such as power failure, the registration center can automatically delete the provider information
• When the registration center restarts, the registration data and subscription requests can be automatically restored
• When the session expires, the registration data and subscription request can be automatically restored
• When <dubbo:registry check="false" /> is set, the failed registration and subscription requests will be recorded, and the background will retry periodically
• You can set zookeeper login information through <dubbo:registry username="admin" password="1234" />
• The root node of zookeeper can be set through <dubbo:registry group="dubbo" />, if not configured, the default root node will be used.
• Support * wildcard <dubbo:reference group="*" version="*" />, you can subscribe to all groups of services and providers of all versions

4.2 Dubbo3 node structure