Document URL: https://access.redhat.com/documentation/en/openshift-enterprise/3.1/installation-and-configuration/chapter-2-installing#configuring-ansible Section Number and Name: 2.4.3.2 Describe the issue: Here is what the note says NOTE When specifying multiple etcd hosts, external etcd is installed and configured. Clustering of OpenShift’s embedded etcd is not supported. Here is what Mike said http://post-office.corp.redhat.com/archives/aos-devel/2015-November/msg00542.html Suggestions for improvement: Fix the defect Additional information:
This was not meant to suggest that they could not be collocated, just that if you specify multiple etcd hosts, the standalone version of etcd is installed, instead of the etcd that is embedded in OpenShift itself. Calling it "external etcd" is probably the confusion here, but also we can add some language specifically about collocation to clear things up.
Yes clarifying on colocation will help. During my interaction with the customer, I said that colocation is possible and customer pointed this out and I got confused. Based on your answer I understand that colocation is actually possible. It also helps if we clarify whether the 3 masters (or odd number of masters) are required for the purpose of colocation with etcd. Can we manage with 2 masters for HA if etcd is not collocated? Or are there any other implications?
The master services themselves have no quorum or requirement that they have an odd number of hosts. However, obviously for HA you need at least two and the overwhelming majority of installations colocate etcd and master services so it just makes sense to have three uniform hosts.
Removed note referencing embedded etcd (since it is no longer supported in 3.7+): [3.7] https://github.com/openshift/openshift-docs/pull/9492 [master] https://github.com/openshift/openshift-docs/pull/9491 (It was already removed in 3.9 and 3.10 for some reason.) Updated changes for 3.6: https://github.com/openshift/openshift-docs/pull/9495 Based on review there, 3.5 PR incoming.
3.5 and 3.6 changes reviewed and merged: [3.5] https://github.com/openshift/openshift-docs/pull/9498 [3.6] https://github.com/openshift/openshift-docs/pull/9495
https://docs.openshift.com/container-platform/3.5/architecture/infrastructure_components/kubernetes_infrastructure.html#high-availability-masters