High Availability

MMR supports horizontal scaling and by consequence high availability capabilities as well. Near-zero downtime can be achieved by employing rolling upgrades of a horizontally-scaled cluster.

In all cases, machine ID 0 must be updated first, however all other processes can be updated in any order.

For a given version number vX.Y.Z:

• A change in X indicates a breaking change to MMR. The entire cluster should be brought offline to perform the upgrade. Check the upgrade notes for further guidance on zero-downtime upgrades to this version.
• A change in Y indicates a large but backwards compatible change to MMR. The cluster should be upgraded quickly, but does not need to be taken offline first. A higher volume of errors may happen while the cluster is upgraded.
• A change in Z indicates a patch or otherwise small backwards compatible change to MMR. The cluster can be upgraded more slowly, and does not need to be taken offline first.