Azure App Service Windows: Error UNKNOWN starting Next.JS Standalone

Question

I would be glad for any tips on how to debug this?

• next.js standalone on node.js 18.19.1 on windows Azure Web App.

• The app starts locally (via the /build/standalone folde )

• package.json has a : "start": "node server.js"

• The port 3000 indicates that process.env.PORT is not set by azure?

  (node:6588) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead. (Use node --trace-deprecation ... to show where the warning was created) ⨯ Failed to start server Error: listen UNKNOWN: unknown error 0.0.0.0:3000 at Server.setupListenHandle [as _listen2] (node:net:1817:16) at listenInCluster (node:net:1865:12) at doListen (node:net:2014:7) at process.processTicksAndRejections (node:internal/process/task_queues:83:21) { code: 'UNKNOWN', errno: -1, syscall: 'listen', address: '0.0.0.0', port: 3000 }

Answer 1

I created Sample Nextjs Standalone app and deployed to Azure web app service windows.

In next.config file I have set the output to standalone.

next.config.mjs:

const nextConfig = {
  output: 'standalone',
}
export default nextConfig;

For deploying nextjs app to Azure Web App Windows I added web.config and server.js files to root directory of the project.

To avoid the error use below server.js file.

server.js:

const { createServer } = require("http");
const next = require("next");
const port = process.env.PORT || 3000;
const dev = process.env.NODE_ENV !== "production";
const app = next({ dev });
const handle = app.getRequestHandler();
app.prepare().then(() => {
  createServer((req, res) => {
    handle(req, res);
  }).listen(port, (err) => {
    if (err) throw err;
    console.log(`> Ready on http://localhost:${port}`);
  });
});

web.config:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.webServer>
WebSocket support -->
    <webSocket enabled="false" />
    <handlers>
      <add name="iisnode" path="server.js" verb="*" modules="iisnode"/>
    </handlers>
    <rewrite>
      <rules>
        <rule name="NodeInspector" patternSyntax="ECMAScript" stopProcessing="true">
          <match url="^server.js\/debug[\/]?" />
        </rule>
        <rule name="StaticContent">
          <action type="Rewrite" url="public{REQUEST_URI}"/>
        </rule>
        <rule name="DynamicContent">
          <conditions>
            <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="True"/>
          </conditions>
          <action type="Rewrite" url="server.js"/>
        </rule>
      </rules>
    </rewrite>
    <security>
      <requestFiltering>
        <hiddenSegments>
          <remove segment="bin"/>
        </hiddenSegments>
      </requestFiltering>
    </security>
    <httpErrors existingResponse="PassThrough" />
       <iisnode watchedFiles="web.config;*.js"/>
  </system.webServer>
</configuration>

I deployed nextjs app to Azure App service through VS code.

Azure Web App Output: