Many applications require binary resources to complete the install process. While it is possible for a charm to download this software from package repositories or other locations, some charms may be deployed in data centers with restrictive firewalls that do not allow access to all areas of the Internet. It may also be desirable to more strictly control what specific resources are deployed.
Starting with Juju 2.0, users can upload resources to the controller or the Juju Charm Store from where they are accessible to charms.
Use discrete files for resources. E.g. if your charm requires a software package and a dependency, then use two resources, one for the software package and one for the dependency. Do not group resources. Keep them discrete. Juju optimizes distribution of resources. If resources are grouped into one file (resource) then they are larger and must be updated everywhere when they are updated.
Charm developers can add a
resources key to the
metadata.yaml file to
define one or more resources.
resources: software: type: file filename: software.zip description: "One line description that is useful when operators need to push it."
filename is what Juju will name the file locally when it is downloaded.
Juju will check the extension on the file being uploaded and will prevent
files with different extensions from being uploaded.
Resources can be uploaded to a local Juju controller, where only charms from that controller can access the resources, or to the Juju Charm Store where access is controlled by permissions assigned to the charms to which the resources are attached.
Users can list the resources that are currently available on the Juju
controller by using the
juju list-resources command. The command shows
resources for a service or a unit.
$ juju list-resources resources-example [Service] RESOURCE SUPPLIED BY REVISION software admin@local 2016-25-05T18:37 $ juju list-resources resources-example/0 [Unit] RESOURCE REVISION software 2016-25-05T18:37
Users can display the resources that are currently available in Juju Charm Store
for a charm or a specific revision number with the
$ charm list-resources cs:~lazypower/etcd [Service] RESOURCE REVISION etcd 0 etcdctl 0
juju attach command uploads a file from local disk to the Juju controller
to be used as a resource for a service. You must specify the charm name, the
resource name and the path to the file.
juju attach charm-name resource-name=filepath
If you attach a resource to a running charm the
upgrade-charm hook is run.
This gives charm authors the ability to handle new resources appropriately.
Resources may be uploaded to the Juju controller at deploy time by specifying the --resource flag followed by resource-name=filepath pair. This flag may be repeated more than once to upload more than one resource.
juju deploy charm-name --resource foo=/some/file.tgz --resource bar=./docs/cfg.xml
Where "foo" and "bar" are the resource names in the
metadata.yaml file for the
charm attach command uploads a file to the Juju Charm Store as a new
resource for the charm. You must specify the fully qualified charm name, including
the version. e.g. ~you/mycharm-0 instead of just ~you/mycharm.
charm attach ~mbruzek/trusty/consul-0 software=./consul_0.6.4_linux_amd64.zip
The charm command
resource-get will fetch a resource from the Juju
controller or the Juju Charm store. The command returns a local path to the
file for a named resource.
resource-get has not been run for the named resource previously, then the
resource is downloaded from the controller at the revision associated with the
unit's application. That file is stored in the unit's local cache. If
resource-get has been run before then each subsequent run synchronizes the
resource with the controller. This ensures that the revision of the unit-local
copy of the resource matches the revision of the resource associated with the
The path provided by
resource-get references the up-to-date file for the
resource. Note that the resource may get updated on the controller for the
service at any time, meaning the cached copy may be out of date at any time
resource-get is called. Consequently, the command should be run at
every point where it is critical for the resource be up to date.
# resource-get software /var/lib/juju/agents/unit-resources-example-0/resources/software/software.zip