Simulate Index Template API

A SimulateIndexTemplateRequest specifies the indexName to simulate matching against the templates in the system.

SimulateIndexTemplateRequest simulateRequest = new SimulateIndexTemplateRequest("log-000001"); 
PutComposableIndexTemplateRequest newIndexTemplateRequest = new PutComposableIndexTemplateRequest()
    .name("used-for-simulation");
Settings settings = Settings.builder().put("index.number_of_shards", 6).build();
Template template = new Template(settings, null, null); 
ComposableIndexTemplate composableIndexTemplate = new ComposableIndexTemplate(Arrays.asList("log-*"),
    template, null, 90L, null, null);
newIndexTemplateRequest.indexTemplate(composableIndexTemplate);

simulateRequest.indexTemplateV2Request(newIndexTemplateRequest); 

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

ActionListener<SimulateIndexTemplateResponse> listener =
    new ActionListener<SimulateIndexTemplateResponse>() {
        @Override
        public void onResponse(SimulateIndexTemplateResponse response) {
            
        }

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

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 SimulateIndexTemplateRequest 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 simulate-index-template method:

client.indices().simulateIndexTemplateAsync(simulateRequest, 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 simulate-index-template looks like:

ActionListener<SimulateIndexTemplateResponse> listener =
    new ActionListener<SimulateIndexTemplateResponse>() {
        @Override
        public void onResponse(SimulateIndexTemplateResponse response) {
            
        }

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

The returned SimulateIndexTemplateResponse includes a resolved Template object containing the resolved settings, mappings and aliases of the index template that matched and would be applied to the index with the provided name (if any). It will also return a Map of index templates (both legacy and composable) names and their corresponding index patterns:

SimulateIndexTemplateResponse simulateIndexTemplateResponse = client.indices().simulateIndexTemplate(simulateRequest,
    RequestOptions.DEFAULT);
assertThat(simulateIndexTemplateResponse.resolvedTemplate().settings().get("index.number_of_shards"), is("6")); 
assertThat(simulateIndexTemplateResponse.overlappingTemplates().get("my-template"),
    containsInAnyOrder("pattern-1", "log-*"));