Any good ideas to fix “connect() failed (111: Connection refused)” error when restarting nodejs server? - PeakU

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Any good ideas to fix “connect() failed (111: Connection refused)” error when restarting nodejs server?

Background:

I use a Nginx+NodeJS structure to run the website. The server has quite some traffic like 300 concurrent people online. Visiting all kind of pages. And I use pm2 to manage my node apps.

Problem:

However, when I restart the node server with pm2 restart xxx, in a short duration (like 15 seconds), the users will encounter a 502 error. And accordingly, there is “connect() failed (111: Connection refused)” in the log.

According to one other question on SO.

A 502 Bad Gateway error usually suggests that the proxy (Nginx in NodeJS's case) can't find a destination to route the traffic to.

So I guess the error is occurring because of the moment that a user requests the server while the Node hasn't ready for its business. So my Nginx couldn't "contact" my nodejs and threw a 502 error.

Is there any way to fix this?

over 4 years ago · Santiago Trujillo

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If you want to continue serving your users while you restart your Node.js server, you need a second Node.js server. More precisely:

Before the restart, node myapp.js is running and listening on port A. Nginx routes traffic to port A.
Now you can start a second Node.js server, probably on a newer version of your app, node mynewapp.js, that listens on port B. While you do that, traffic is still routed to port A.
Once node mynewapp.js is up and running, you switch Nginx so that it routes traffic to port B.
Allow a grace period for requests on port A to finish, then you can shut down the node myapp.js process.

Note two potential pitfalls with this approach:

Long running requests on port A would prevent you from shutting down the "old" Node.js server.
Requests that leave a state in the Node.js server (in global Javascript variables, say), would lose that state when you switch over to the other Node.js server. But (session) states that you write to a database will survive.

over 4 years ago · Santiago Trujillo Report

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