Prevent ElasticSearchAliasInit jobs overlapping (#1056)

Elasticsearch can only process cluster state changes (e.g. adding new aliases) sequentially on the master node. Running multiple instances of this job (e.g. with the `EnsureElasticSearchAliases` command) can overload the Elasticsearch master node, causing Jobs to fail.

Prevent multiple `ElasticSearchAliasInit` jobs from running at the same time for each Elasticsearch cluster by using the `WithoutOverlapping` middleware [1]

[1]: https://laravel.com/docs/10.x/queues#preventing-job-overlaps

Bug: T416158

Author: outdooracorn

app/Jobs/ElasticSearchAliasInit.php

@@ -5,6 +5,7 @@
 use App\Http\Curl\HttpRequest;
 use App\WikiDb;
 use Illuminate\Foundation\Bus\Dispatchable;
+use Illuminate\Queue\Middleware\WithoutOverlapping;
 use Illuminate\Support\Facades\Log;
 
 class ElasticSearchAliasInit extends Job {
@@ -24,6 +25,18 @@ public function __construct(int $wikiId, string $esHost, ?string $sharedPrefix =
         $this->sharedPrefix = $sharedPrefix ?? getenv('ELASTICSEARCH_SHARED_INDEX_PREFIX');
     }
 
+    /**
+     * Get the middleware the job should pass through.
+     *
+     * @return array<int, object>
+     */
+    public function middleware(): array {
+        return [
+            // Only allow one job per ES host to run at a time to avoid DoSing the ES cluster with alias updates
+            new WithoutOverlapping("elasticsearch-alias-init-{$this->esHost}"),
+        ];
+    }
+
     public function handle(HttpRequest $request) {
         Log::info(__METHOD__ . ": Updating Elasticsearch aliases for $this->wikiId");