Explain Lifecycle API

The Explain Lifecycle API allows you to retrieve information about the execution of a Lifecycle Policy with respect to one or more indices.

ExplainLifecycleRequest request =
    new ExplainLifecycleRequest("my_index-1", "other_index"); 

The returned ExplainLifecycleResponse contains a map of LifecyclePolicyMetadata, accessible by the name of the policy, which contains data about each policy, as well as the policy definition.

Map<String, IndexLifecycleExplainResponse> indices =
    response.getIndexResponses();
IndexLifecycleExplainResponse myIndex = indices.get("my_index-1");
String policyName = myIndex.getPolicyName(); 
boolean isManaged = myIndex.managedByILM(); 

String phase = myIndex.getPhase(); 
long phaseTime = myIndex.getPhaseTime(); 
String action = myIndex.getAction(); 
long actionTime = myIndex.getActionTime();
String step = myIndex.getStep(); 
long stepTime = myIndex.getStepTime();

String failedStep = myIndex.getFailedStep(); 

When executing a ExplainLifecycleRequest in the following manner, the client waits for the ExplainLifecycleResponse to be returned before continuing with code execution:

ExplainLifecycleResponse response = client.indexLifecycle()
    .explainLifecycle(request, RequestOptions.DEFAULT);

Synchronous calls may throw an IOException in case of either failing to parse the REST response in the high-level REST client, the request times out or similar cases where there is no response coming back from the server.

In cases where the server returns a 4xx or 5xx error code, the high-level client tries to parse the response body error details instead and then throws a generic ElasticsearchException and adds the original ResponseException as a suppressed exception to it.

Executing a ExplainLifecycleRequest can also be done in an asynchronous fashion so that the client can return directly. Users need to specify how the response or potential failures will be handled by passing the request and a listener to the asynchronous ilm-explain-lifecycle method:

client.indexLifecycle().explainLifecycleAsync(request,
    RequestOptions.DEFAULT, listener); 

The asynchronous method does not block and returns immediately. Once it is completed the ActionListener is called back using the onResponse method if the execution successfully completed or using the onFailure method if it failed. Failure scenarios and expected exceptions are the same as in the synchronous execution case.

A typical listener for ilm-explain-lifecycle looks like:

ActionListener<ExplainLifecycleResponse> listener =
    new ActionListener<ExplainLifecycleResponse>() {
        @Override
        public void onResponse(ExplainLifecycleResponse response)
        {
            Map<String, IndexLifecycleExplainResponse> indices =
                response.getIndexResponses(); 
        }

        @Override
        public void onFailure(Exception e) {
            
        }
    };