storage #32

Supports: precise


Generic storage charm subordinate. Intended to aid in making charms easier to interface with external storage solutions without having to speak and understand each type. Presents a single mount point on the unit, and communicates that back to your service through the data relation.

Subordinate Storage Charm

This charm aims to allow storage to be mounted and consumed in your juju environment. Simply attach this charm to any that supports the "block-storage" interface, and the charmed application will start writing data into the provided storage.

Provider-Specific Features

NOTE: This charm has a dependency on provider-specific metadata (like instance id). If using the "block-storage-broker" relation to mount stroage from the cloud, you will be limited to:

  • Amazon Web Services
  • Openstack

Other cloud providers are planned for the future, and patches are certainly welcome.

NOTE2: If using this charm to mount filesystems over NFS, provider-specific limitations do not exist.

Sample Deployment

juju deploy <principal charm>
juju deploy storage --config <my_storage_config.yaml>
juju add-relation <principal_charm> storage

Sample Data Relation

The Storage charm is designed to make your life easier as a charm author. Implementing the data relation is very straightforward.

Sample Metadata:

    interface: block-storage
    scope: container
    optional: true

Sample Joined Hook:

relation-set mountpoint=/mnt/mydata

Sample Changed Hook:

mount=`relation-get mountpoint`
if [ -z "$mount" ] ; then
    juju-log "wait for related service to start"
    exit 0
service my_service stop
change_my_service_to_use_mount $mount
service my_service start


  • Support other providers
  • Support relating to other charms via mount, ceph-client, etc.
  • Support config changes?


(string) The backend storage provider. Will be mounted at root, and can be one of, local, block-storage-broker or nfs. If you set to block-storage-broker, you should provide a suitable value for volume_size.
(string) The root path where external directories will be mounted.
(string) YAML map as e.g. "{postgres/0: vol-0000010, postgres/1: vol-0000016}". A service unit to specific block storage volume-id that should be attached to each unit. This requires that provider is set to block-storage-broker and that volume-ids specified match a listing from nova volume-list. If a related unit does not have a volume-id specified, a new volume of volume_size will be created for that unit.
(int) The volume size in GB to request from the block-storage-broker.