Charm Metadata Reference
The full spec for a charm’s metadata (metadata.yaml) is as follows:
# (Required) The name of the charm. Determines URL in Charmhub and the name administrators
# will ultimately use to deploy the charm. E.g. `juju deploy <name>`
name: <name>
# (Required) A short, one-line description of the charm
summary: <summary>
# (Required) A full description of the configuration layer
description: |
<description>
# (Optional) A list of maintainers in the format "First Last <email>"
maintainers:
- <maintainer>
# (Optional) A list of terms that any charm user must agree with
terms:
- <term>
# (Optional) True if the charm is meant to be deployed as a subordinate to a
# principal charm
subordinate: true | false
# (Optional) A map of containers to be created adjacent to the charm. This field
# is required when the charm is targetting Kubernetes, where each of the specified
# containers will be created as sidecars to the charm in the same pod.
containers:
# Each key represents the name of the container
<container name>:
# Note: One of either resource or bases must be specified.
# (Optional) Reference for an entry in the resources field. Specifies
# the oci-image resource used to create the container. Must not be
# present if a base/channel is specified
resource: <resource name>
# (Optional) A list of bases in descending order of preference for use
# in resolving a container image. Must not be present if resource is
# specified. These bases are listed as base (instead of name) and
# channel as in the Base definition, as an unnamed top-level object list
bases:
# Name of the OS. For example ubuntu/centos/windows/osx/opensuse
- name: <base name>
# Channel of the OS in format "track[/risk][/branch]" such as used by
# Snaps. For example 20.04/stable or 18.04/stable/fips
channel: <track[/risk][/branch]>
# List of architectures that this particular charm can run on
architectures:
- <architecture>
# (Optional) List of mounted storages for this container
mounts:
# (Required) Name of the storage to mount from the charm storage
- name: <storage name>
# (Optional) In the case of filesystem storages, the location to
# mount the storage. For multi-stores, the location acts as the
# parent directory for each mounted store.
location: <path>
# (Optional) Additional resources that accompany the charm
resources:
# Each key represents the name of the resource
<resource name>:
# (Required) The type of the resource
type: file | oci-image
# (Optional) Description of the resource and its purpose
description: <description>
# (Required: when type:file) The filename of the resource as it should
# appear in the filesystem
filename: <filename>
# (Optional) Map of relations provided by this charm
provides:
# Each key represents the name of the relation as known by this charm
<relation name>:
# (Required) The interface schema that this relation conforms to
interface: <interface name>
# (Optional) Maximum number of supported connections to this relation
# endpoint. This field is an integer
limit: <n>
# (Optional) Defines if the relation is required. Informational only.
optional: true | false
# (Optional) The scope of the relation. Defaults to "global"
scope: global | container
# (Optional) Map of relations required by this charm
requires:
# Each key represents the name of the relation as known by this charm
<relation name>:
# (Required) The interface schema that this relation conforms to
interface: <interface name>
# (Optional) Maximum number of supported connections to this relation
# endpoint. This field is an integer
limit: <n>
# (Optional) Defines if the relation is required. Informational only.
optional: true | false
# (Optional) The scope of the relation. Defaults to "global"
scope: global | container
# (Optional) Mutual relations between units/peers of this charm
peer:
# Each key represents the name of the relation as known by this charm
<relation name>:
# (Required) The interface schema that this relation conforms to
interface: <interface name>
# (Optional) Maximum number of supported connections to this relation
# endpoint. This field is an integer
limit: <n>
# (Optional) Defines if the relation is required. Informational only.
optional: true | false
# (Optional) The scope of the relation. Defaults to "global"
scope: global | container
# (Optional) Storage requests for the charm
storage:
# Each key represents the name of the storage
<storage name>:
# (Required) Type of the requested storage
type: filesystem | block
# (Optional) Description of the storage requested
description: <description>
# (Optional) The mount location for filesystem stores. For multi-stores
# the location acts as the parent directory for each mounted store.
location: <location>
# (Optional) Indicates if all units of the application share the storage
shared: true | false
# (Optional) Indicate if the storage should be made read-only (where possible)
read-only: true | false
# (Optional) The number of storage instances to be requested
multiple: <n> | <n>-<m> | <n>- | <n>+
# (Optional) Minimum size of requested storage in forms G, GiB, GB. Size
# multipliers are M, G, T, P, E, Z or Y. With no multiplier supplied, M
# is implied.
minimum-size: <n>| <n><multiplier>
# (Optional) List of properties, only supported value is "transient"
properties:
- transient
# (Optional) Device requests for the charm, for example a GPU
devices:
# Each key represents the name of the device
<device name>:
# (Required) The type of device requested
type: gpu | nvidia.com/gpu | amd.com/gpu
# (Optional) Description of the requested device
description: <description>
# (Optional) Minimum number of devices required
countmin: <n>
# (Optional) Maximum number of devices required
countmax: <n>
# (Optional) Extra bindings for the charm. For example binding extra network
# interfaces. Key only map, value must be blank. Key represents the name
extra-bindings:
# Key only map; key represents the name of the binding
<binding name>:
Example metadata.yaml
Below is an example of a metadata.yaml file for a Kubernetes charm
name: super-charm
summary: a really great charm
description: |
This is a really great charm, whose metadata is suitably complete so as to
demonstrate as many of the fields as possible.
maintainers:
- Joe Bloggs <joe.bloggs@email.com>
containers:
super-app:
resource: super-app-image
mounts:
- name: logs
location: /logs
super-app-helper:
bases:
- name: ubuntu
channel: ubuntu/20.04
architectures:
- amd64
- arm64
resources:
super-app-image:
type: oci-image
description: OCI image for the Super App (hub.docker.com/_/super-app)
definitions:
type: file
description: A small SQLite3 database of definitions needed by super app
filename: definitions.db
provides:
super-worker:
interface: super-worker
requires:
ingress:
interface: ingress
optional: true
limit: 1
peer:
super-replicas:
interface: super-replicas
storage:
logs:
type: filesystem
location: /logs
description: Storage mount for application logs
shared: true
Last updated 9 days ago.