Fix issue where NextServer.prepare wouldn't be called when deployed

packages/next/src/server/base-server.ts

@@ -534,6 +534,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     res: BaseNextResponse,
     parsedUrl?: NextUrlWithParsedQuery
   ): Promise<void> {
+    await this.prepare()
     const method = req.method.toUpperCase()
     return getTracer().trace(
       BaseServerSpan.handleRequest,
@@ -968,8 +969,18 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     this.renderOpts.assetPrefix = prefix ? prefix.replace(/\/$/, '') : ''
   }
 
-  // Backwards compatibility
-  public async prepare(): Promise<void> {}
+  protected preparedPromise: Promise<void> | null = null
+  /**
+   * Runs async initialization of server.
+   * It is idempotent, won't fire underlying initialization more than once.
+   */
+  public async prepare(): Promise<void> {
+    if (this.preparedPromise === null) {
+      this.preparedPromise = this.prepareImpl()
+    }
+    return this.preparedPromise
+  }
+  protected async prepareImpl(): Promise<void> {}
 
   // Backwards compatibility
   protected async close(): Promise<void> {}

packages/next/src/server/dev/next-dev-server.ts

@@ -873,7 +873,7 @@ export default class DevServer extends Server {
     }
   }
 
-  async prepare(): Promise<void> {
+  protected async prepareImpl(): Promise<void> {
     setGlobal('distDir', this.distDir)
     setGlobal('phase', PHASE_DEVELOPMENT_SERVER)
 
@@ -907,7 +907,7 @@ export default class DevServer extends Server {
         telemetry,
       })
     }
-    await super.prepare()
+    await super.prepareImpl()
     await this.addExportPathMapRoutes()
     await this.hotReloader?.start()
     await this.startWatcher()

packages/next/src/server/next-server.ts

@@ -327,8 +327,8 @@ export default class NextNodeServer extends BaseServer {
     setHttpClientAndAgentOptions(this.nextConfig)
   }
 
-  public async prepare() {
-    await super.prepare()
+  protected async prepareImpl() {
+    await super.prepareImpl()
     if (
       !this.serverOptions.dev &&
       this.nextConfig.experimental.instrumentationHook
@@ -1639,6 +1639,9 @@ export default class NextNodeServer extends BaseServer {
   }
 
   public getRequestHandler(): NodeRequestHandler {
+    // This is just optimization to fire prepare as soon as possible
+    // It will be properly awaited later
+    void this.prepare()
     const handler = super.getRequestHandler()
     return async (req, res, parsedUrl) => {
       return handler(this.normalizeReq(req), this.normalizeRes(res), parsedUrl)

packages/next/src/server/next.ts

@@ -126,7 +126,12 @@ export class NextServer {
 
   async prepare() {
     const server = await this.getServer()
-    return server.prepare()
+
+    // We shouldn't prepare the server in production,
+    // because this code won't be executed when deployed
+    if (this.options.dev) {
+      await server.prepare()
+    }
   }
 
   async close() {
@@ -135,12 +140,15 @@ export class NextServer {
   }
 
   private async createServer(options: DevServerOptions): Promise<Server> {
+    let ServerImplementation: typeof Server
     if (options.dev) {
-      const DevServer = require('./dev/next-dev-server').default
-      return new DevServer(options)
+      ServerImplementation = require('./dev/next-dev-server').default
+    } else {
+      ServerImplementation = await getServerImpl()
     }
-    const ServerImplementation = await getServerImpl()
-    return new ServerImplementation(options)
+    const server = new ServerImplementation(options)
+
+    return server
   }
 
   private async loadConfig() {