ES Client: use ClusterConnectionPool (elastic#134628)

(cherry picked from commit 6decdc3)

# Conflicts:
#	src/core/server/elasticsearch/client/configure_client.ts

src/core/server/elasticsearch/client/configure_client.test.ts

@@ -17,6 +17,7 @@ import {
   ClientMock,
 } from './configure_client.test.mocks';
 import { loggingSystemMock } from '../../logging/logging_system.mock';
+import { ClusterConnectionPool } from '@elastic/elasticsearch';
 import type { ElasticsearchClientConfig } from './client_config';
 import { configureClient } from './configure_client';
 import { instrumentEsQueryAndDeprecationLogger } from './log_query_and_deprecation';
@@ -112,6 +113,21 @@ describe('configureClient', () => {
     expect(client).toBe(ClientMock.mock.results[0].value);
   });
 
+  it('constructs a client using `ClusterConnectionPool` for `ConnectionPool` ', () => {
+    const mockedTransport = { mockTransport: true };
+    createTransportMock.mockReturnValue(mockedTransport);
+
+    const client = configureClient(config, { logger, type: 'test', scoped: false });
+
+    expect(ClientMock).toHaveBeenCalledTimes(1);
+    expect(ClientMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        ConnectionPool: ClusterConnectionPool,
+      })
+    );
+    expect(client).toBe(ClientMock.mock.results[0].value);
+  });
+
   it('calls instrumentEsQueryAndDeprecationLogger', () => {
     const client = configureClient(config, { logger, type: 'test', scoped: false });
 

src/core/server/elasticsearch/client/configure_client.ts

@@ -6,7 +6,7 @@
  * Side Public License, v 1.
  */
 
-import { Client, HttpConnection } from '@elastic/elasticsearch';
+import { Client, HttpConnection, ClusterConnectionPool } from '@elastic/elasticsearch';
 import { Logger } from '../../logging';
 import { parseClientOptions, ElasticsearchClientConfig } from './client_config';
 import { instrumentEsQueryAndDeprecationLogger } from './log_query_and_deprecation';
@@ -35,6 +35,8 @@ export const configureClient = (
     ...clientOptions,
     Transport: KibanaTransport,
     Connection: HttpConnection,
+    // using ClusterConnectionPool until https://github.com/elastic/elasticsearch-js/issues/1714 is addressed
+    ConnectionPool: ClusterConnectionPool,
   });
 
   instrumentEsQueryAndDeprecationLogger({ logger, client, type });