Add/Remove Monitors¶
With ceph-deploy, adding and removing monitors is a simple task. You just
add or remove one or more monitors on the command line with one command. Before
ceph-deploy, the process of adding and removing monitors involved
numerous manual steps. Using ceph-deploy imposes a restriction: you may
only install one monitor per host.
Note
We do not recommend commingling monitors and OSDs on the same host.
For high availability, you should run a production Ceph cluster with AT LEAST three monitors. Ceph uses the Paxos algorithm, which requires a consensus among the majority of monitors in a quorum. With Paxos, the monitors cannot determine a majority for establishing a quorum with only two monitors. A majority of monitors must be counted as such: 1:1, 2:3, 3:4, 3:5, 4:6, etc.
See Monitor Config Reference for details on configuring monitors.
Add a Monitor¶
Once you create a cluster and install Ceph packages to the monitor host(s), you
may deploy the monitor(s) to the monitor host(s). When using ceph-deploy,
the tool enforces a single monitor per host.
ceph-deploy mon create {host-name [host-name]...}
Note
Ensure that you add monitors such that they may arrive at a consensus
among a majority of monitors, otherwise other steps (like ceph-deploy gatherkeys)
will fail.
Note
When adding a monitor on a host that was not in hosts initially defined
with the ceph-deploy new command, a public network statement needs
to be added to the ceph.conf file.
Remove a Monitor¶
If you have a monitor in your cluster that you’d like to remove, you may use
the destroy option.
ceph-deploy mon destroy {host-name [host-name]...}
Note
Ensure that if you remove a monitor, the remaining monitors will be able to establish a consensus. If that is not possible, consider adding a monitor before removing the monitor you would like to take offline.
