Microservices Engine:Empty list protection

Limits

The Nacos Java client in 1.4.1 or later supports empty list protection.

Procedure

• If you use the Nacos Java client, perform the following operations:

  1. Add the following dependency of the Nacos client:

     <!-- ${nacos-client.version} must be 1.4.1 or later. -->
     <dependency>
         <groupId>com.alibaba.nacos</groupId>
         <artifactId>nacos-client</artifactId>
         <version>${nacos-client.version}</version>
     </dependency>

  2. Configure the following settings in the application code:

     Properties properties = new Properties();
     properties.put(PropertyKeyConst.SERVER_ADDR, "${Endpoint of the MSE Nacos instance}");
     properties.put(PropertyKeyConst.NAMING_PUSH_EMPTY_PROTECTION, "true");
     NamingService naming = NamingFactory.createNamingService(properties);

• If your application is a Spring Cloud Alibaba application, add the following configuration to the configuration file of your application:

  spring.cloud.nacos.discovery.namingPushEmptyProtection=true

• If your application is a Dubbo application, add the following registry URL configuration to the configuration file of your Dubbo application:

  dubbo.registry.address=nacos://${Endpoint of the MSE Nacos instance}:8848?namingPushEmptyProtection=true

Limits

The Nacos engine version must be 2.1.0.0 or later. For more information about how to upgrade the Nacos engine version, see Update a Nacos version.

Procedure

The method to enable empty list protection varies based on the version of your MSE Nacos engine.

• If the version of your MSE Nacos engine is 2.1.0.0 or 2.1.0.1, no operation is required. Empty list protection is automatically enabled in these versions.

• If the version of your MSE Nacos engine is 2.1.0.2 or later, perform the following steps to enable empty list protection:

  1. Log on to the MSE console, and select a region in the top navigation bar.

  2. In the left-side navigation pane, choose Microservices Registry > Instances.

  3. On the Instances page, click the name of the instance.

  4. In the left-side navigation pane, click Parameter Settings. In the Real-time Effective Parameters section of the Parameter Settings page, click Edit in the Actions column of the forcePushEmptyProtectionForAllService parameter.

  5. In the Edit Parameters dialog box, select Yes for Value and click OK.

     Note

     To ensure the highest service availability, we recommend that you select Yes for Value of the forcePushEmptyProtectionForAllService parameter in all cases.

Verify the result

When a service triggers empty list protection, Trigger push empty protection for Service is displayed in the naming.log file in the ${user.home}/logs/nacos directory of the node where the consumer resides.

In normal cases, such information does not frequently appear. If such information frequently appears, you can troubleshoot this issue based on the following possible causes:

• The providers to which the consumer subscribes do not exist.

  If the consumer subscribes to a non-existing provider, you must check whether the application dependency is required. If the application dependency is not required, delete the invalid dependency. If the application dependency is required, you must publish the provider again.

• No providers are displayed in the instance list.

  • Check whether the providers to which the consumer subscribes are frequently disconnected.

  • Check whether the network connection between each provider and the MSE Nacos instance is normal. If the network connection is abnormal, the MSE Nacos instance determines that the provider is disconnected.

Identify the service that triggers empty list protection

The error message contains the information about the service that triggers empty list protection. You can identify the empty service to which the consumer subscribes based on Service{namespace='XXX', group='xx', name='xxxxxxx', ephemeral=true, revision=0}.

Known trigger scenarios

Scenarios in which empty list protection is forcefully enabled

In MSE Nacos 2.1.0.2 or later, the logic for enabling empty list protection is optimized. This optimization ensures that empty list protection is enabled only if Yes is selected for Value of the forcePushEmptyProtectionForAllService parameter. However, the system still automatically enables empty list protection to ensure availability and stability in the following scenarios even if No is selected for Value of the forcePushEmptyProtectionForAllService parameter.

• When an engine node is upgraded, restarted, or recovered from a failure, the node automatically enables two-minute empty list protection for all applications to ensure service availability during the period of time.

• If all instances of an application are removed from the application instance list on the MSE instance, the MSE instance automatically enables one-minute empty list protection for the application. This operation prevents empty list protection from being unexpectedly triggered when issues such as unstable network performance and temporary failures of service providers occur. This way, service availability is provided in this scenario.