Preserve backing index ordering for data streams (#63749) (#63903)

Author: danhermann

server/src/main/java/org/elasticsearch/action/admin/indices/resolve/ResolveIndexAction.java

@@ -579,7 +579,6 @@ private static void enrichIndexAbstraction(String indexAbstraction, SortedMap<St
                     case DATA_STREAM:
                         IndexAbstraction.DataStream dataStream = (IndexAbstraction.DataStream) ia;
                         String[] backingIndices = dataStream.getIndices().stream().map(i -> i.getIndex().getName()).toArray(String[]::new);
-                        Arrays.sort(backingIndices);
                         dataStreams.add(new ResolvedDataStream(
                             dataStream.getName(),
                             backingIndices,

server/src/test/java/org/elasticsearch/action/admin/indices/resolve/ResolveIndexTests.java

@@ -47,6 +47,7 @@
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.cluster.DataStreamTestHelper.createTimestampField;
+import static org.hamcrest.Matchers.arrayContaining;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.core.IsNull.notNullValue;
@@ -169,6 +170,29 @@ public void testResolveWithMultipleNames() {
         validateDataStreams(dataStreams, "logs-mysql-test");
     }
 
+    public void testResolvePreservesBackingIndexOrdering() {
+        Metadata.Builder builder = Metadata.builder();
+        String dataStreamName = "my-data-stream";
+        String[] names = {"not-in-order-2", "not-in-order-1", DataStream.getDefaultBackingIndexName(dataStreamName, 3)};
+        List<IndexMetadata> backingIndices = Arrays.stream(names).map(n -> createIndexMetadata(n, true)).collect(Collectors.toList());
+        for (IndexMetadata index : backingIndices) {
+            builder.put(index, false);
+        }
+
+        DataStream ds = new DataStream(dataStreamName, createTimestampField("@timestamp"),
+            backingIndices.stream().map(IndexMetadata::getIndex).collect(Collectors.toList()));
+        builder.put(ds);
+
+        IndicesOptions indicesOptions = IndicesOptions.LENIENT_EXPAND_OPEN_CLOSED_HIDDEN;
+        List<ResolvedIndex> indices = new ArrayList<>();
+        List<ResolvedAlias> aliases = new ArrayList<>();
+        List<ResolvedDataStream> dataStreams = new ArrayList<>();
+        TransportAction.resolveIndices(new String[]{"*"}, indicesOptions, builder.build(), resolver, indices, aliases, dataStreams, true);
+
+        assertThat(dataStreams.size(), equalTo(1));
+        assertThat(dataStreams.get(0).getBackingIndices(), arrayContaining(names));
+    }
+
     private void validateIndices(List<ResolvedIndex> resolvedIndices, String... expectedIndices) {
         assertThat(resolvedIndices.size(), equalTo(expectedIndices.length));
         for (int k = 0; k < resolvedIndices.size(); k++) {