Why do we use multi application server instances on the same server

Question

I guess there is a good reason, but I don\'t understand why sometimes we put for example 5 instances having the same webapplications on the same physical server.

Has it

Answer 1

I would suggest you use around least JVM per NUMA region. If a single JVM uses more than one NUMA region (often a single CPU) the performance can degrade significantly, due to a significant increase in the cost of accessing main memory of another CPU.

Additionally using multiple servers can allow you to

• use different versions of java or your your applications server.
• isolate different applications which could interfere (they shouldn't but they might)
• limit GC pause times between services.

EDIT: It could be historical. There may have been any number of reasons to have separate JVMs in the past but since you don't know what they were, you don't know if they still apply and it may be simpler to leave things as they are.