Behaviour when reducing instances of a Bluemix application

Question

I have an orchestrator service which keeps track of the instances that are running and what request they are currently dealing with. If a new instance is required, I make a REST call to increase the instances and wait for the new instance to connect to the orchestrator. It's one request per instance.

The orchestrator tracks whether an instance is doing anything and knows which instances can be stopped, however there is nothing in the API that allows me to reduce the number of instances stopping a particular instance, which is what I am trying to achieve.

Is there anything I can do to manipulate the platform into deterministically stopping the instances that I want to stop? Perhaps by having long running HTTP requests to the instances I require and killing the request when it's no longer required, then making the API call to reduce the number of instances?

Part of the issue here is that I don't know the specifics of the current behavior...

Answer 1

Assuming you're talking about CloudFoundry/Instant Runtime applications, all of the instances of an applications are running behind a load balancer which uses round-robin to distribute requests across the instances (unless you have session affinity cookie set up). Differentiating between each instances for incoming requests or manual scaling is not recommended and it's an anti-pattern. You can not control which instance the scale down task will choose.

If you really want that level of control with each instance, maybe you should deploy them as separate applications. MyApp1, MyApp2, MyApp3, etc. All of your applications can have the same route (myapp.mybluemix.net). Each of the applications can now distinguish themselves by their name (VCAP_APPLICATION) allowing you terminate them.