TripleO network/controller servers HA

asked 2016-12-02 11:02:06 -0600

nuriel77 gravatar image

Is it possible to have two controller nodes instead of three?

I understand that three are needed for achieving quorum, but have only two baremetal nodes in current cluster where I can deploy controllers onto.

Thanks in advance!

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answered 2016-12-12 15:50:22 -0600

dbaxps gravatar image

updated 2016-12-12 16:09:39 -0600

1. What is a cluster manager?
See original text
For these reasons (text above this line), we highly recommend the use of a cluster manager like Pacemaker.
2. Deployment flavors

It is possible to deploy three different flavors of the Pacemaker architecture. The two extremes are Collapsed (where every component runs on every node) and Segregated (where every component runs in its own 3+ node cluster).

Regardless of which flavor you choose, we recommend that clusters contain at least three nodes so that you can take advantage of quorum.

Quorum becomes important when a failure causes the cluster to split in two or more partitions. In this situation, you want the majority members of the system to ensure the minority are truly dead (through fencing) and continue to host resources. For a two-node cluster, no side has the majority and you can end up in a situation where both sides fence each other, or both sides are running the same services. This can lead to data corruption.

See also
Page 45
Enrty "Galera" Based on write set replication (wsrep)

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answered 2016-12-12 14:01:45 -0600

nuriel77 gravatar image

updated 2016-12-12 16:08:14 -0600

Answering myself: No, not possible. HA architecture in TripleO is for 3 nodes, 2 nodes would not work (after having done some testing).

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Asked: 2016-12-02 08:40:37 -0600

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Last updated: Dec 12 '16