# Dynamic Configuration

This document describes how the Sermant plugin uses the dynamic configuration function.

Dynamic configuration function is one of the core services of sermant-core module (opens new window). This feature allows Sermant to pull configurations from a dynamic configuration center for rich and diverse service governance capabilities.

Refer to Sermant Dynamic Configuration Center User Manual (opens new window) on how to use the dynamic configuration center. The following section describes how to develop dynamic-configuration-related capabilities in plugins.

# Dynamic Configuration API

The functionality API of Dynamic Configuration Service is provided by the abstract class DynamicConfigService (opens new window) , which implements three interfaces, as seen in API (opens new window) directory, The concrete interface is as follows:：

Above all, two concepts need to be clear:

• Key, a single reference to a dynamical configuration key
• Group, a dynamical configuration set of groups, often used to distinguish between users

As you can see, the above API is mainly divided into data adding, deleting, querying and modifying operations, and add/remove operations of the listener's DynamicConfigListener (opens new window). The latter event callback is a crucial part of the functionality of the Dynamic Configuration Service, which is the main feature of the plugin using Dynamic Configuration Service.

Also, in the KeyService (opens new window) interface, all the API defined are API without Group. They will actually use the default Group and be fixed to API of KeyGroupService (opens new window) in DynamicConfigService (opens new window). The default Group can be modified via dynamic.config.default_group in the unified configuration file config.properties.

Finally, besides the above service interfaces, there are a few other interfaces, configurations, or entities that developers need to pay attention to:

• Static configuration DynamicConfig (opens new window) for Dynamic Configuration Service, whose parameters configuration refers to Sermant Dynamic Configuration Center User Manual (opens new window) .

• Dynamic configuration service implementation typeDynamicConfigServiceType (opens new window), contains:

  Enum	Explanation
  ZOOKEEPER	ZooKeeper
  KIE	ServiceComb Kie
  NOP	No implementation

• Dynamic configuration listener DynamicConfigListener (opens new window), which contains the following interface methods:

  Method	Explanation
  void process(DynamicConfigEvent (opens new window))	Callback interface for handling change events of configuration

• Change events of dynamic configuration DynamicConfigEvent (opens new window), whose member properties are as follows:

  Type	Property	Explanation
  String	key	Key of configuration
  String	group	Group of configuration
  String	content	Content of configuration
  DynamicConfigEventType (opens new window)	changeType	Type of configuration change event

• Type of change events of dynamic configuration DynamicConfigEventType (opens new window), which contains following four kinds:

  Enum	Explanation
  INIT	Initial response when adding a listener
  CREATE	Event of adding new configuration
  MODIFY	Event of modifying configuration
  DELETE	Event of deleting configuration

# Dynamic Configuration Development Example

The DynamicConfigService instance of the dynamic configuration function can be obtained with the following code:

DynamicConfigService service = ServiceManager.getService(DynamicConfigService.class);

Once the service instance is obtained, you can invoke the API listed in the table above to take the appropriate action. For example, to register a listener, you can do this by:

// ${group} is user group，${key} is the key listened. For zookeeper, the path is: / + ${group} + ${key}
// if ${group} do not exist，it will set the value by dynamicconfig.default_group in unified configuration
service.addConfigListener("${key}", "${group}", new DynamicConfigListener() {
  @Override
  public void process(ConfigChangedEvent event) {
    // do something
  }
});

Once the listener is registered, the process method will be triggered when the server creates, deletes, modifies, or adds child nodes.

Examples of other interfaces are not listed here, you can refer to the API description above.