Thank you Clayton. This is much useful info.
After your explanation, leaning towards separation of master and etcd servers.
From: "ccoleman redhat com" <ccoleman redhat com>
Date: Wednesday, January 6, 2016 at 4:05 PM
To: Jason DeTiberus <jdetiber redhat com>
Cc: skotaru <skotaru cisco com>, "dev lists openshift redhat com" <dev lists openshift redhat com>, "users lists openshift redhat com" <users lists openshift redhat com>
Subject: Re: master and etcd installation
On Jan 6, 2016, at 12:23 PM, Jason DeTiberus <jdetiber redhat com> wrote:
Specifically on memory:
The master (specifically the controller) keeps caches of frequently used cluster information, so the larger your cluster gets the more memory the Openshift controller process will require (the elected master only). The API server part tends to generate a fair amount of memory churn through garbage collection, but does not necessarily need a large resident set. Etcd, in most deployments, will typically use more memory than both master processes combined.
Up until etcd + master memory is 50% of your host total memory, it's probably easier to run both on the same machine. Past that, keeping them separate will likely result in more predictable behavior and avoid OOM events (occasionally, in rare scenarios, etcd can OOM if asked to retrieve very large portions of its key space in a single call - in practice Openshift does not do this but it is possible).