Delete data stream in ILM delete action if last index in data stream (#69637)

If an index happens to be the last index in the data stream (such as a user testing ILM out) when it
comes to the `delete` action, we attempt to delete it, however, a data stream cannot be empty, so it
throws an exception and prevents the deletion.

This commit changes the behavior of the `delete` action such that deleting the very last index in a
data stream deletes the entire data stream.

Author: dakrone

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/DeleteStep.java

@@ -14,6 +14,7 @@
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexAbstraction;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.xpack.core.action.DeleteDataStreamAction;
 
 import java.util.Locale;
 
@@ -38,7 +39,14 @@ public void performDuringNoSnapshot(IndexMetadata indexMetadata, ClusterState cu
 
         if (dataStream != null) {
             assert dataStream.getWriteIndex() != null : dataStream.getName() + " has no write index";
-            if (dataStream.getWriteIndex().getIndex().getName().equals(indexName)) {
+            if (dataStream.getIndices().size() == 1 && dataStream.getIndices().get(0).equals(indexMetadata)) {
+                // This is the last index in the data stream, the entire stream
+                // needs to be deleted, because we can't have an empty data stream
+                DeleteDataStreamAction.Request deleteReq = new DeleteDataStreamAction.Request(new String[]{dataStream.getName()});
+                getClient().execute(DeleteDataStreamAction.INSTANCE, deleteReq,
+                    ActionListener.wrap(response -> listener.onResponse(true), listener::onFailure));
+                return;
+            } else if (dataStream.getWriteIndex().getIndex().getName().equals(indexName)) {
                 String errorMessage = String.format(Locale.ROOT, "index [%s] is the write index for data stream [%s]. " +
                         "stopping execution of lifecycle [%s] as a data stream's write index cannot be deleted. manually rolling over the" +
                         " index will resume the execution of the policy as the index will not be the data stream's write index anymore",

x-pack/plugin/ilm/qa/multi-node/src/javaRestTest/java/org/elasticsearch/xpack/ilm/TimeSeriesDataStreamsIT.java

@@ -19,6 +19,7 @@
 import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.test.rest.ESRestTestCase;
 import org.elasticsearch.xpack.core.ilm.CheckNotDataStreamWriteIndexStep;
+import org.elasticsearch.xpack.core.ilm.DeleteAction;
 import org.elasticsearch.xpack.core.ilm.ForceMergeAction;
 import org.elasticsearch.xpack.core.ilm.FreezeAction;
 import org.elasticsearch.xpack.core.ilm.LifecycleSettings;
@@ -46,6 +47,7 @@
 import static org.elasticsearch.xpack.TimeSeriesRestDriver.getStepKeyForIndex;
 import static org.elasticsearch.xpack.TimeSeriesRestDriver.indexDocument;
 import static org.elasticsearch.xpack.TimeSeriesRestDriver.rolloverMaxOneDocCondition;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.is;
 
@@ -238,6 +240,18 @@ public void testGetDataStreamReturnsILMPolicy() throws Exception {
         assertThat(logsDataStream.get("ilm_policy"), is(policyName));
     }
 
+    public void testDeleteOnlyIndexInDataStreamDeletesDataStream() throws Exception {
+        createNewSingletonPolicy(client(), policyName, "delete", new DeleteAction(false));
+        createComposableTemplate(client(), template, dataStream + "*", getTemplate(policyName));
+        indexDocument(client(), dataStream, true);
+
+        assertBusy(() -> {
+            Request r = new Request("GET", "/_data_stream/" + dataStream);
+            Exception e = expectThrows(Exception.class, () -> client().performRequest(r));
+            assertThat(e.getMessage(), containsString("no such index [" + dataStream + "]"));
+        });
+    }
+
     private static Template getTemplate(String policyName) throws IOException {
         return new Template(getLifecycleSettings(policyName), null, null);
     }