Juju Charm - Ceph MON
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Ceph is a distributed storage and network file system designed to provide excellent performance, reliability, and scalability.

This charm deploys a Ceph monitor cluster.


Boot things up by using:

juju deploy -n 3 ceph-mon

By default the ceph-mon cluster will not bootstrap until 3 service units have been deployed and started; this is to ensure that a quorum is achieved prior to adding storage devices.


This charm supports pausing and resuming ceph’s health functions on a cluster, for example when doing maintenance on a machine. To pause or resume, call:

juju action do --unit ceph-mon/0 pause-health or juju action do --unit ceph-mon/0 resume-health

Scale Out Usage

You can use the Ceph OSD and Ceph Radosgw charms:

Rolling Upgrades

ceph-mon and ceph-osd charms have the ability to initiate a rolling upgrade. This is initiated by setting the config value for source. To perform a rolling upgrade first set the source for ceph-mon. Watch juju status. Once the monitor cluster is upgraded proceed to setting the ceph-osd source setting. Again watch juju status for output. The monitors and osds will sort themselves into a known order and upgrade one by one. As each server is upgrading the upgrade code will down all the monitor or osd processes on that server, apply the update and then restart them. You will notice in the juju status output that the servers will tell you which previous server they are waiting on.

Supported Upgrade Paths

Currently the following upgrade paths are supported using the Ubuntu Cloud Archive:

  • trusty-firefly -> trusty-hammer
  • trusty-hammer -> trusty-jewel

Firefly is available in Trusty, Hammer is in Trusty-Juno (end of life), Trusty-Kilo, Trusty-Liberty, and Jewel is available in Trusty-Mitaka.

For example if the current config source setting is: cloud:trusty-liberty changing that to cloud:trusty-mitaka will initiate a rolling upgrade of the monitor cluster from hammer to jewel.

Edge cases

There’s an edge case in the upgrade code where if the previous node never starts upgrading itself then the rolling upgrade can hang forever. If you notice this has happened it can be fixed by setting the appropriate key in the ceph monitor cluster. The monitor cluster will have keys that look like ceph-mon_ip-ceph-mon-0_1484680239.573482_start and ceph-mon_ip-ceph-mon-0_1484680274.181742_stop. What each server is looking for is that stop key to indicate that the previous server upgraded successfully and it’s safe to take itself down. If the stop key is not present it will wait 10 minutes, then consider that server dead and move on.

Network Space support

This charm supports the use of Juju Network Spaces, allowing the charm to be bound to network space configurations managed directly by Juju. This is only supported with Juju 2.0 and above.

Network traffic can be bound to specific network spaces using the public (front-side) and cluster (back-side) bindings:

juju deploy ceph-mon --bind "public=data-space cluster=cluster-space"

alternatively these can also be provided as part of a Juju native bundle configuration:

  charm: cs:xenial/ceph-mon
  num_units: 1
    public: data-space
    cluster: cluster-space

Please refer to the Ceph Network Reference for details on how using these options effects network traffic within a Ceph deployment.

NOTE: Spaces must be configured in the underlying provider prior to attempting to use them.

NOTE: Existing deployments using ceph-*-network configuration options will continue to function; these options are preferred over any network space binding provided if set.

NOTE: The monitor-hosts field is only used to migrate existing clusters to a juju managed solution and should be left blank otherwise.

Contact Information


Report bugs on Launchpad


Technical Footnotes

This charm uses the new-style Ceph deployment as reverse-engineered from the Chef cookbook at https://github.com/ceph/ceph-cookbooks, although we selected a different strategy to form the monitor cluster. Since we don’t know the names or addresses of the machines in advance, we use the relation-joined hook to wait for all three nodes to come up, and then write their addresses to ceph.conf in the “mon host” parameter. After we initialize the monitor cluster a quorum forms quickly, and OSD bringup proceeds.

See the documentation for more information on Ceph monitor cluster deployment strategies and pitfalls.