fix(core): Initialize application only once

Fixes #12006

packages/core/nest-application.ts

@@ -177,6 +177,10 @@ export class NestApplication
   }
 
   public async init(): Promise<this> {
+    if (this.isInitialized) {
+      return this;
+    }
+
     this.applyOptions();
     await this.httpAdapter?.init();
 

packages/core/test/nest-application.spec.ts

@@ -7,6 +7,7 @@ import { NestApplication } from '../nest-application';
 import { mapToExcludeRoute } from './../middleware/utils';
 import { NoopHttpAdapter } from './utils/noop-adapter.spec';
 import { MicroserviceOptions } from '@nestjs/microservices';
+import * as sinon from 'sinon';
 
 describe('NestApplication', () => {
   describe('Hybrid Application', () => {
@@ -79,4 +80,28 @@ describe('NestApplication', () => {
       });
     });
   });
+  describe('Double initialization', () => {
+    it('should initialize application only once', async () => {
+      const noopHttpAdapter = new NoopHttpAdapter({});
+      const httpAdapterSpy = sinon.spy(noopHttpAdapter);
+
+      const applicationConfig = new ApplicationConfig();
+
+      const container = new NestContainer(applicationConfig);
+      container.setHttpAdapter(noopHttpAdapter);
+
+      const instance = new NestApplication(
+        container,
+        noopHttpAdapter,
+        applicationConfig,
+        new GraphInspector(container),
+        {},
+      );
+
+      await instance.init();
+      await instance.init();
+
+      expect(httpAdapterSpy.init.calledOnce).to.be.true;
+    });
+  });
 });