sunbeam-charms/ops-sunbeam/doc/howto-config-context.rst
Guillaume Boutry 822bfb0f50 Fix documentation typos
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How-To Write a config context
=============================
A config context is an additional context that is passed to the template
renderer in its own namespace. They are usually useful when some logic
needs to be applied to user supplied charm configuration. The context
has access to the charm object.
Below is an example which applies logic to the charm config as well as
collecting the application name to construct the context.
.. code:: python
class CinderCephConfigurationContext(ConfigContext):
"""Cinder Ceph configuration context."""
def context(self) -> None:
"""Cinder Ceph configuration context."""
config = self.charm.model.config.get
data_pool_name = config('rbd-pool-name') or self.charm.app.name
if config('pool-type') == "erasure-coded":
pool_name = (
config('ec-rbd-metadata-pool') or
f"{data_pool_name}-metadata"
)
else:
pool_name = data_pool_name
backend_name = config('volume-backend-name') or self.charm.app.name
return {
'cluster_name': self.charm.app.name,
'rbd_pool': pool_name,
'rbd_user': self.charm.app.name,
'backend_name': backend_name,
'backend_availability_zone': config('backend-availability-zone'),
}
Configuring Charm to use custom config context
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The charm can append the new context onto those provided by the base class.
.. code:: python
import ops_sunbeam.charm as sunbeam_charm
class MyCharm(sunbeam_charm.OSBaseOperatorAPICharm):
"""Charm the service."""
@property
def config_contexts(self) -> List[sunbeam_ctxts.ConfigContext]:
"""Configuration contexts for the operator."""
contexts = super().config_contexts
contexts.append(
sunbeam_ctxts.CinderCephConfigurationContext(self, "cinder_ceph"))
return contexts