Question

As far as I understand, a Node.js server is basically a JavaScript file, run by the node executable. Is it possible to update this file without stopping request handling?

I guess the node executable must be stopped for this, so I think I should use a reverse proxy. For example:

1. Original server version listens on localhost:50001
2. Proxy server listens to requests on webinterface:80 and forwards them to localhost:50001
3. New server version should be started on localhost:50002
4. Proxy server forwarding target should be changed to localhost:50002
5. Original server version should be stopped

Is this a valid approach? How can such a version update be done automatically on multiple server machines (accessible from the same LAN)?

Answer 1

A different “pure-node” solution is to use the built-in cluster module:

Your code runs as one cluster-client (of many). A cluster-server process binds to the port and does automatic load-balancing between clients. When you’ve changed the code, you can send a signal to the cluster-server and it will gracefully restart your clients, without dropping any existing connections.

Here are some projects that can do the cluster-server management for you:

• https://npmjs.org/package/cluster-master
• https://github.com/daeq/node-cluster-manager.

Advantages:

• Fewer components in your stack. (Easier to deploy / manage.)
• Can automatically start a node process for each core on the CPU, so your program can fully leverage the underlying hardware.
• No need to learn nginx’s config syntax