org.apache.dubbo.registry.client.ServiceDiscovery SPI.In the Service Discovery chapter, we learned about the usage and working principles of several core built-in registry implementations in Dubbo, such as Nacos and Zookeeper. This article explains how to provide a custom registry implementation by extending the org.apache.dubbo.registry.client.ServiceDiscovery and org.apache.dubbo.registry.nacos.NacosServiceDiscoveryFactory SPI.
For the complete source code of this example, please refer to dubbo-registry-etcd. In addition to this example, many registry extension implementations in the core repository apache/dubbo and the extension library apache/dubbo-spi-extensions can serve as references for extensions:
# Common registry implementations supported by Dubbo
nacos=org.apache.dubbo.registry.nacos.NacosServiceDiscoveryFactory
zookeeper=org.apache.dubbo.registry.zookeeper.ZookeeperServiceDiscoveryFactory
Implement the etcd registry based on extending SPI.
First, implement the ServiceDiscoveryFactory interface by extending AbstractServiceDiscoveryFactory
public class EtcdServiceDiscoveryFactory extends AbstractServiceDiscoveryFactory {
@Override
protected ServiceDiscovery createDiscovery(URL registryURL) {
return new EtcdServiceDiscovery(applicationModel, registryURL);
}
}
Some key methods and implementations of EtcdServiceDiscovery are as follows:
public class EtcdServiceDiscovery extends AbstractServiceDiscovery {
private final Set<String> services = new ConcurrentHashSet<>();
private final Map<String, InstanceChildListener> childListenerMap = new ConcurrentHashMap<>();
EtcdClient etcdClient;
public EtcdServiceDiscovery(ApplicationModel applicationModel, URL registryURL) {
super(applicationModel, registryURL);
EtcdTransporter etcdTransporter = applicationModel.getExtensionLoader(EtcdTransporter.class).getAdaptiveExtension();
etcdClient = etcdTransporter.connect(registryURL);
etcdClient.addStateListener(state -> {
if (state == StateListener.CONNECTED) {
try {
recover();
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}
});
this.registryURL = registryURL;
}
@Override
public void doRegister(ServiceInstance serviceInstance) {
try {
String path = toPath(serviceInstance);
etcdClient.putEphemeral(path, new Gson().toJson(serviceInstance));
services.add(serviceInstance.getServiceName());
} catch (Throwable e) {
throw new RpcException("Failed to register " + serviceInstance + " to etcd " + etcdClient.getUrl()
+ ", cause: " + (OptionUtil.isProtocolError(e)
? "etcd3 registry may not be supported yet or etcd3 registry is not available."
: e.getMessage()), e);
}
}
@Override
protected void doUnregister(ServiceInstance serviceInstance) {
try {
String path = toPath(serviceInstance);
etcdClient.delete(path);
services.remove(serviceInstance.getServiceName());
} catch (Throwable e) {
throw new RpcException("Failed to unregister " + serviceInstance + " to etcd " + etcdClient.getUrl() + ", cause: " + e.getMessage(), e);
}
}
@Override
public void addServiceInstancesChangedListener(ServiceInstancesChangedListener listener) throws NullPointerException, IllegalArgumentException {
for (String serviceName : listener.getServiceNames()) {
registerServiceWatcher(serviceName, listener);
}
}
@Override
public List<ServiceInstance> getInstances(String serviceName) {
List<String> children = etcdClient.getChildren(toParentPath(serviceName));
if (CollectionUtils.isEmpty(children)) {
return Collections.emptyList();
}
List<ServiceInstance> list = new ArrayList<>(children.size());
for (String child : children) {
ServiceInstance serviceInstance = new Gson().fromJson(etcdClient.getKVValue(child), DefaultServiceInstance.class);
list.add(serviceInstance);
}
return list;
}
}
Add the following configuration in the resources/META-INF/dubbo/org.apache.dubbo.registry.client.ServiceDiscoveryFactory file:
etcd=org.apache.dubbo.registry.etcd.EtcdServiceDiscoveryFactory
To enable etcd as the registry, modify the registry configuration in the resources/application.properties file as follows:
dubbo.registry.address=etcd://host:port