Fix to use keep-alive in standalone mode (#50221)

You can specify keepAliveTimeout as an environment variable in
standalone mode, but there is a problem with it not being properly
applied.

#46052 

#### before
<img width="574" alt="2023-05-24 12 49 12"
src="https://github.com/vercel/next.js/assets/90969158/9014252e-dcac-4b32-805a-68e844e853b1">
<img width="574" alt="2023-05-24 12 49 20"
src="https://github.com/vercel/next.js/assets/90969158/8c5672b2-8af8-4751-aa0c-7347428c3cbb">

#### after

<img width="574" alt="2023-05-24 1 19 12"
src="https://github.com/vercel/next.js/assets/90969158/96a83b0d-1dd1-45b7-b053-e0103185dd47">

Author: doinki

packages/next/src/build/utils.ts

@@ -1955,6 +1955,10 @@ if (!process.env.NEXT_MANUAL_SIG_HANDLE) {
 const currentPort = parseInt(process.env.PORT, 10) || 3000
 const hostname = process.env.HOSTNAME || 'localhost'
 const keepAliveTimeout = parseInt(process.env.KEEP_ALIVE_TIMEOUT, 10);
+const isValidKeepAliveTimeout =
+  !Number.isNaN(keepAliveTimeout) &&
+  Number.isFinite(keepAliveTimeout) &&
+  keepAliveTimeout >= 0;
 const nextConfig = ${JSON.stringify({
       ...serverConfig,
       distDir: `./${path.relative(dir, distDir)}`,
@@ -1967,6 +1971,7 @@ createServerHandler({
   hostname,
   dir,
   conf: nextConfig,
+  keepAliveTimeout: isValidKeepAliveTimeout ? keepAliveTimeout : undefined,
 }).then((nextHandler) => {
   const server = http.createServer(async (req, res) => {
     try {
@@ -1978,13 +1983,10 @@ createServerHandler({
     }
   })
 
-  if (
-    !Number.isNaN(keepAliveTimeout) &&
-      Number.isFinite(keepAliveTimeout) &&
-      keepAliveTimeout >= 0
-  ) {
+  if (isValidKeepAliveTimeout) {
     server.keepAliveTimeout = keepAliveTimeout
   }
+
   server.listen(currentPort, async (err) => {
     if (err) {
       console.error("Failed to start server", err)

packages/next/src/server/lib/render-server-standalone.ts

@@ -11,12 +11,14 @@ export const createServerHandler = async ({
   dir,
   dev = false,
   minimalMode,
+  keepAliveTimeout,
 }: {
   port: number
   hostname: string
   dir: string
   dev?: boolean
   minimalMode: boolean
+  keepAliveTimeout?: number
 }) => {
   const routerWorker = new Worker(require.resolve('./render-server'), {
     numWorkers: 1,
@@ -65,6 +67,7 @@ export const createServerHandler = async ({
     minimalMode,
     workerType: 'router',
     isNodeDebugging: false,
+    keepAliveTimeout,
   })
   didInitialize = true