Keep a node application running on azure app service

Question

I have deployed a node js web application on app service in azure. Issue is that my application occasionally getting killed for unknown reason. I have done exhaustive search through all the log fines using kudu.

If I restart app service, application starts working.

Is there any way I can restart my node application once it has crashed. Kind of run for ever no matter what. For example if any error happens in an asp.net code deployed in IIS, IIS never crashes, its keeps of serving other incoming request.

Something like using forever/pm2 in azure app service.

Answer 1

node.js in Azure App Services is powered by IISNode, which takes care of everything you described, including monitoring your process for failures and restarting it.

Consider the following POC:

var http = require('http');    
http.createServer(function (req, res) {
    if (req.url == '/bad') {
        throw 'bad';
    }
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('bye');
}).listen(process.env.PORT || 1337);

If I host this in a Web App and issue the following sequence of requests:

1. GET /
2. GET /bad
3. GET /

Then the first will yield HTTP 200, the second will throw on the server and yield HTTP 500, and the third will yield HTTP 200 without me having to do anything. IISNode will just detect the crash and restart the process.

So you shouldn't need PM2 or similar solution because this is built in with App Services. However, if you really want to, they now have App Services Preview on Linux, which is powered by PM2 and lets you configure PM2. More on this here. But again you get this out of the box already.

Another thing to consider is Always On setting which is on by default:

By default, web apps are unloaded if they are idle for some period of time. This lets the system conserve resources. In Basic or Standard mode, you can enable Always On to keep the app loaded all the time. If your app runs continuous web jobs, you should enable Always On, or the web jobs may not run reliably.

This is another possible root cause for your issue and the solution is to disable Always On for your Web App (see the link above).