[StorageIndexAdapter] Set auto_expand_replicas to fix yellow health on single-node ES clusters

src/platform/packages/shared/kbn-storage-adapter/src/index_adapter/index.test.ts

@@ -76,6 +76,7 @@ const createMockEsClient = () => {
         template: { mappings: {} },
       }),
       putMapping: jest.fn().mockResolvedValue({}),
+      putSettings: jest.fn().mockResolvedValue({}),
     },
   } as unknown as jest.Mocked<ElasticsearchClient>;
   return client;
@@ -162,6 +163,24 @@ describe('StorageIndexAdapter - transport options forwarding', () => {
     );
   });
 
+  it('includes settings in the index template', async () => {
+    const adapter = new StorageIndexAdapter(esClient, loggerMock, storageSettings);
+    const client = adapter.getClient();
+
+    await client.index({ id: 'doc1', document: { foo: 'bar' } });
+
+    expect(esClient.indices.putIndexTemplate).toHaveBeenCalledWith(
+      expect.objectContaining({
+        template: expect.objectContaining({
+          settings: expect.objectContaining({
+            auto_expand_replicas: '0-1',
+            number_of_shards: 1,
+          }),
+        }),
+      })
+    );
+  });
+
   it('works without transport options (backward compatible)', async () => {
     const adapter = new StorageIndexAdapter(esClient, loggerMock, storageSettings);
     const client = adapter.getClient();

src/platform/packages/shared/kbn-storage-adapter/src/index_adapter/index.ts

@@ -160,6 +160,10 @@ export class StorageIndexAdapter<
     const version = getSchemaVersion(this.storage);
 
     const template: IndicesPutIndexTemplateIndexTemplateMapping = {
+      settings: {
+        auto_expand_replicas: '0-1',
+        number_of_shards: 1,
+      },
       mappings: {
         _meta: {
           version,
@@ -319,11 +323,13 @@ export class StorageIndexAdapter<
     if (!writeIndex) {
       this.logger.debug(`Creating index`);
       await this.createIndex();
-    } else if (writeIndex?.state.mappings?._meta?.version !== expectedSchemaVersion) {
-      this.logger.debug(`Updating mappings of existing index due to schema version mismatch`);
-      await this.updateMappingsOfExistingIndex({
-        name: writeIndex.name,
-      });
+    } else {
+      if (writeIndex.state.mappings?._meta?.version !== expectedSchemaVersion) {
+        this.logger.debug(`Updating mappings of existing index due to schema version mismatch`);
+        await this.updateMappingsOfExistingIndex({
+          name: writeIndex.name,
+        });
+      }
     }
 
     return await cb();

src/platform/packages/shared/kbn-storage-adapter/src/index_adapter/integration_tests/index.test.ts

@@ -656,6 +656,10 @@ describe('StorageIndexAdapter', () => {
         is_write_index: true,
       },
     });
+
+    expect(getIndexResponse[writeIndexName].settings?.index?.auto_expand_replicas).toEqual('0-1');
+
+    expect(getIndexResponse[writeIndexName].settings?.index?.number_of_shards).toEqual('1');
   }
 
   async function verifyClean() {