Configure Monitor Election Strategies

By default, the monitors will use the classic mode. We recommend that you stay in this mode unless you have a very specific reason.

If you want to switch modes BEFORE constructing the cluster, change the mon election default strategy option. This option is an integer value:

  • 1 for “classic”

  • 2 for “disallow”

  • 3 for “connectivity”

Once your cluster is running, you can change strategies by running

$ ceph mon set election_strategy {classic|disallow|connectivity}

Choosing a mode

The modes other than classic provide different features. We recommend you stay in classic mode if you don’t need the extra features as it is the simplest mode.

The disallow Mode

This mode lets you mark monitors as disallowd, in which case they will participate in the quorum and serve clients, but cannot be elected leader. You may wish to use this if you have some monitors which are known to be far away from clients. You can disallow a leader by running

$ ceph mon add disallowed_leader {name}

You can remove a monitor from the disallowed list, and allow it to become a leader again, by running

$ ceph mon rm disallowed_leader {name}

The list of disallowed_leaders is included when you run

$ ceph mon dump

The connectivity Mode

This mode evaluates connection scores provided by each monitor for its peers and elects the monitor with the highest score. This mode is designed to handle network partitioning or net-splits, which may happen if your cluster is stretched across multiple data centers or otherwise has a non-uniform or unbalanced network topology.

This mode also supports disallowing monitors from being the leader using the same commands as above in disallow.

Examining connectivity scores

The monitors maintain connection scores even if they aren’t in the connectivity election mode. You can examine the scores a monitor has by running

ceph daemon mon.{name} connection scores dump

Scores for individual connections range from 0-1 inclusive, and also include whether the connection is considered alive or dead (determined by whether it returned its latest ping within the timeout).

While this would be an unexpected occurrence, if for some reason you experience problems and troubleshooting makes you think your scores have become invalid, you can forget history and reset them by running

ceph daemon mon.{name} connection scores reset

While resetting scores has low risk (monitors will still quickly determine if a connection is alive or dead, and trend back to the previous scores if they were accurate!), it should also not be needed and is not recommended unless requested by your support team or a developer.