Scaling up – running multiple Notes instances

Now that we've got ourselves a running application, you'll have played around a bit and created, read, updated, and deleted many notes.

Suppose for a moment that this isn't a toy application, but one that is interesting enough to draw millions of users a day. Serving a high load typically means adding servers, load balancers, and many other things. A core part of this is to have multiple instances of the application running at the same time to spread the load.

Let's see what happens when you run multiple instances of the Notes application at the same time.

The first thing is to make sure the instances are on different ports. In app.mjs, you'll see that setting the PORT environment variable controls the port being used. If the PORT variable is not set, it defaults to http://localhost:3000, or what we've been using all along.

Let's open up package.json and add the following lines to the scripts section...