How many instances are recommended for a ColdFusion 2018 license?

This is a difficult question to answer without more information. The point of running multiple instances is to separate one application from another, so that a failure of one doesn't affect the other. There are two reasons why you might do this. One is to provide redundancy on a single server, so that you have two or more instances all running the same codebase, and perhaps clustered with a single web server (or responding to multiple web servers that are themselves clustered behind a load balancer, etc, etc). The other is to separate different applications - for example, you might have one application that just doesn't run all that well, and when it fails it stops all the other applications from running. Those are two different use cases, and they might make different assumptions about memory use.

But if you don't have either of those use cases, you're probably best served by having a single instance that can address all of the RAM and use all of the CPU that you have available. Modern Java applications are quite capable of doing this, unlike in the "old days" of 32-bit applications. So, just because you can run multiple instances doesn't mean you should.

Dave Watts, Eidolon LLC