Is it necessary to install 3 master nodes in openshift?

Question

I am trying to bring up Openshift cluster on hardware. By default, Openshift recommends to install 3 master and 3 worker nodes.

I have to install containers and pods on the worker nodes. Since my hardware has a resource crunch which can not accommodate 6 nodes, Can I install 1 master and 3 worker nodes? Will it affect any functionality?

Answer 1

Can I install 1 master and 3 worker nodes,Will it affect any functionality?

Yes for 3.11. Single master means your control plane has no HA.

No for 4.10.

Answer 2

You can not install 1 master and 3 workers and expect it to work correctly, when the documentation clearly says minimum requirement for control plane is three machines.

3 nodes control plane is required for High Availability. If you are able sacrifice high availability, perhaps you should rethink If you really need Openshift for this task.

Or, if this is an edge computing workload you can follow single node openshift installation: https://docs.openshift.com/container-platform/4.10/installing/installing_sno/install-sno-preparing-to-install-sno.html

Answer 3

If you deploy only 1 master, the cluster will have difficulties to automatically update the cluster when rolling restart are done.

You can however install a cluster with only 3 masters and no dedicated workers. You'll need to change the scheduler restriction that forbid to deploy user workload on master nodes

It can be done at installation time: Creating the Kubernetes manifest and Ignition config files (flag"mastersSchedulable")

Or later by changing the scheduler operator. doc here

Answer 4

Yes you can. You can go down as to even have a single node cluster as explained here. but you might be better off with deploying a 3-node clusters, making the 3 master nodes also workers, leaving almost all of the functionality intact

PAY ATTENTION as stated above in the comments some functionality won't work, since 2 master nodes are needed for some of the actions.