We have a web application, running on Google Cloud. It's still in development at the moment. We've got a load balancer tied to three separate instance groups, for three different functions, all of them running in Tomcat 8 servers.
One of these instance groups, I'll call it the report group, had been running the same WAR file for several months, and we just, within the past hour, updated it.
Before the update, I'd never seen the report group exceed a single instance. Just before the update, I looked at Tomcat Manager on that instance, and it was showing over a thousand active sessions.
After the update, we ran a test, and POOF, we had two instances, and looking at their Tomcat Managers, they were each showing a few hundred sessions, but an aggregate total of well under 1000. At one point, as I was typing this, it briefly went up to four instances.
Can somebody offer me any insight into what happened, why the behavior changed, and how load balancers and instance groups decide to spawn off additional instances?
And how to keep the instances from multiplying like excessively frisky gerbils?