[7.17] Wait between instances, but not after the last one (#190679) (#…

…190702)

# Backport

This will backport the following commits from `main` to `7.17`:
- [Wait between instances, but not after the last one
(#190679)](#190679)

<!--- Backport version: 8.9.8 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Alejandro Fernández
Haro","email":"[email protected]"},"sourceCommit":{"committedDate":"2024-08-19T12:46:15Z","message":"Wait
between instances, but not after the last one
(#190679)","sha":"965b0a675d537f3a83dcf7eaa6153a33af1b62f4","branchLabelMapping":{"^v8.16.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Core","release_note:skip","backport:all-open","v8.16.0"],"number":190679,"url":"https://github.com/elastic/kibana/pull/190679","mergeCommit":{"message":"Wait
between instances, but not after the last one
(#190679)","sha":"965b0a675d537f3a83dcf7eaa6153a33af1b62f4"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v8.16.0","labelRegex":"^v8.16.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/190679","number":190679,"mergeCommit":{"message":"Wait
between instances, but not after the last one
(#190679)","sha":"965b0a675d537f3a83dcf7eaa6153a33af1b62f4"}},{"url":"https://github.com/elastic/kibana/pull/190694","number":190694,"branch":"8.15","state":"OPEN"}]}]
BACKPORT-->

Co-authored-by: Elastic Machine <[email protected]>

src/core/server/saved_objects/migrationsv2/integration_tests/multiple_kibana_nodes.test.ts

@@ -98,8 +98,10 @@ async function createRoot({ logFileName }: CreateRootConfig) {
   return root;
 }
 
-// FLAKY: https://github.com/elastic/kibana/issues/107864
-describe.skip('migration v2', () => {
+// suite is very long, the 10mins default can cause timeouts
+jest.setTimeout(15 * 60 * 1000);
+
+describe('migration v2', () => {
   let esServer: kbnTestServer.TestElasticsearchUtils;
   let rootA: Root;
   let rootB: Root;
@@ -121,9 +123,7 @@ describe.skip('migration v2', () => {
     },
   };
 
-  afterAll(async () => {
-    await new Promise((resolve) => setTimeout(resolve, 10000));
-  });
+  const delay = (timeInMs: number) => new Promise((resolve) => setTimeout(resolve, timeInMs));
 
   beforeEach(async () => {
     await removeLogFiles();
@@ -157,23 +157,35 @@ describe.skip('migration v2', () => {
   });
 
   afterEach(async () => {
-    await Promise.all([rootA.shutdown(), rootB.shutdown(), rootC.shutdown()]);
+    try {
+      await Promise.all([rootA.shutdown(), rootB.shutdown(), rootC.shutdown()]);
+    } catch (e) {
+      /* trap */
+    }
 
     if (esServer) {
       await esServer.stop();
     }
   });
 
-  const delay = (timeInMs: number) => new Promise((resolve) => setTimeout(resolve, timeInMs));
   const startWithDelay = async (instances: Root[], delayInSec: number) => {
     const promises: Array<Promise<unknown>> = [];
+    const errors: string[] = [];
     for (let i = 0; i < instances.length; i++) {
-      promises.push(instances[i].start());
-      if (i < instances.length - 1) {
+      promises.push(
+        instances[i].start().catch((err) => {
+          errors.push(err.message);
+        })
+      );
+      if (i < instances.length - 2) {
+        // We wait between instances, but not after the last one
         await delay(delayInSec * 1000);
       }
     }
-    return Promise.all(promises);
+    await Promise.all(promises);
+    if (errors.length) {
+      throw new Error(`Failed to start all instances: ${errors.join(',')}`);
+    }
   };
 
   it('migrates saved objects normally when multiple Kibana instances are started at the same time', async () => {