[GitHub] [dubbo] plusmancn removed a comment on issue #8666: [3.0] The problem collection of Triple with ApplicationDiscovery

[GitBox <gi...@apache.org>]

plusmancn removed a comment on issue #8666:
URL: https://github.com/apache/dubbo/issues/8666#issuecomment-913655259


   ## The logic of preferredProtocol was not user-friendly, we maybe should optimize it.
   
   ### What's the problem?
   When we only use the `triple` protocol in dubbo with setting provider's register-mode as `instance`, the consumer can't find the service.
   
   
   The source is in `org.apache.dubbo.config.metadata.ServiceInstanceHostPortCustomizer`, let's have a look:
   
   
   ```java
   @Override
   public void customize(ServiceInstance serviceInstance) {
       String host = null;
       int port = -1;
       // ......
       Set<URL> urls = writableMetadataService.getExportedServiceURLs();
       if (CollectionUtils.isNotEmpty(urls)) {
           ApplicationModel applicationModel = serviceInstance.getApplicationModel();
           String preferredProtocol = applicationModel.getCurrentConfig().getProtocol();
           //  The default value of preferredProtocol is dubbo.
           if (preferredProtocol != null) {
               for (URL exportedURL : urls) {
                   // The protocol of exportedURL is tri
                   // because of tri != dubbo, the host and port will not be assigned values.
                   if (preferredProtocol.equals(exportedURL.getProtocol())) {
                       host = exportedURL.getHost();
                       port = exportedURL.getPort();
                       break;
                   }
               }
           } else {
               URL url = urls.iterator().next();
               host = url.getHost();
               port = url.getPort();
           }
           // If not the port of instace > 0, the application instance will not be registered to RegistryCenter(like Nacos, Zookeeper).
           // As a result, the consumer can't find the avaliabe providers when our settging is registry-mode=instance
           if (serviceInstance instanceof DefaultServiceInstance) {
               DefaultServiceInstance instance = (DefaultServiceInstance) serviceInstance;
               instance.setHost(host);
               instance.setPort(port);
           }
       }
   }
   ```
   
   
   For the moment, if you want both consumer and provider to force using `Application Discovery` in tri protocol, just change one line config of provider as follows:
   
   
   ```yaml
   dubbo:
     application:
       metadata-type: remote
       register-mode: instance
       protocol: tri  <==== HERE, set preferredProtocol as tri
   ```
   
   
   
   
   ### The possible solution
   change the default `application-protocol` as `TRIPLE` in the future
   > Why not now? Because most users are still trying to migrate from 2.0 to 3.0
   
   ```java
   // => org.apache.dubbo.config.ApplicationConfig#checkDefault
   protected void checkDefault() {
       super.checkDefault();
       if (protocol == null) {
           protocol = DUBBO;   // <======= HERE
       }
       // ......
   }
   ```
   In `ServiceInstanceHostPortCustomizer`, If the default protocol not exists, just try to get the first protocol and log an error log.
   


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