How do we decrease the Master Instance for Rancher without killing ourselves?

Got a puzzle for you:

We had someone intro Rancher to us – and left :worried: after setting up our cluster with three Master nodes (m4.large) running.

Other reading suggests that the Master nodes should be much smaller - like t2.small :thinking: - and we are concerned that we could cause a fall down of our cluster.

Any suggestions on sizing of Master nodes? And suggestions on how to migrate?

All help welcome. Thanks in advance! :grinning:


Running on EC2 with Rancher 1.5.6 with 3 Master nodes (behind an ELB) and 3 Worker nodes

I don’t have a lot of experience with large clusters, because we run small clusters and don’t do a lot of churn with deployments.

However, I suspect m4.large may be larger than you need for the master nodes. “Too large” probably won’t cause anything to crash, but you might see a substantial cost savings with smaller nodes. List price on those m4.large EC2 nodes is $159.48/month (less if you set up a prepaid option). We have been using t2.medium master nodes, which list at $36.51/month, and things run just fine. The t2.small would be $18.94/month, but we haven’t tried that and probably won’t, just because that drops to a single vCPU.

You are still running rancher-v1.5.6 (2017-04-24). If you are using kubernetes orchestration, you are still running kubernetes-v1.5.4. If you could upgrade to rancher-v1.6.10 (2017-09-20), you would also upgrade to kubernetes-v1.7.4. We upgraded and it seems very stable for us. We’re quite happy, but the upgrade did involve downtime and a rebuild, as we expected. We didn’t attempt the docker upgrade because of the kubernetes dependency.

Good grief, I copied the wrong line from my notes.

Those m4.large nodes list at $81.16/month. It is a step up to the double-sized m4.xlarge nodes that is $159.48/month.

Thanks @dvdcrn -

Yeah - we thought as much, the fear is that tearing them down and replacing them might be problematic.
Not sure how to decommission them and bring up new ones.

Any recommendations? We had a suggestion to use web-hooks, just not sure how that will work.


I presume you are using an external database as the backend for your Rancher servers. If so, you should be able to just run the same command that used to start the first Rancher servers on the new smaller host. If you are using an external database, then there should not be any data on the hosts running the server. You can start a 4th rancher server, and add it to the cluster, and then remove one of the larger hosts, and then repeat.

Of course, I would recommend that you test this in the lab to make sure that it works correctly, but that should work.