96 lines
3.8 KiB
Markdown
96 lines
3.8 KiB
Markdown
# Overview
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This interface provides a mechanism for 'plugins' to the the Manila charm to
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provide configuration sections/parts to to the Manila charm.
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It is intended to be used to enable manila share backends to be configured
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independently of the main charm, so that vendors/maintainers can supply their
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own backend configuration charms as the project continues.
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# Manila usage
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This interface is used between the Manila charm (share backend role or all) to
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provide the manila service user auth details to backend configuraiton charms,
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and to obtain configuration information that needs to be written into 8
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No explicit handler is required to consume this interface in charms
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that consume this interface.
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The interface provides `manila-plugin.connected` and `manila-plugin.available`
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states.
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## For a Manila backend subordinate charm
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A Manila subordinate charm uses this interface to configure the manila
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configuration files to 'plugin' its functionality. e.g. the generic backend
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needs authentication information (the manila service user) so that it can
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generate the configuration information for nova, neutron and cinder as part of
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the backend configuration in manila.conf.
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The generic charm then needs to set the configuration that the manila principal
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charm will use to write the manila.conf and other files. i.e. the manila charm
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will fold in the data presented into the its configuration information.
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## How the conversation 'goes' between the principal (manila) and subordinate
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1. Juju connects the two charms.
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2. When the 'requires' side connects (hook
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`{requires:manila-plugin}-relation-joined` fires), the Manila principal
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charm will receive the state({relation_name}.connected).
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3. When the 'provides' side connect (hook
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`{provides:manila-plugin}-relation-joined` fires) the subordinate charm
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will receive the state({relation_name}.connected).
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4. When the Manila charm has received keystone authentication information it
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will set that on the relation, and on receipt the 'provides' side will set
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the `{relation_name}.available` state. This allows the providing
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charm (subordinate backend) to use this information.
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5. If the subordinate needs the auth info, then it should block until
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`{relation_name}.available` is available.
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6. The subordinate should present its configuration information on the
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interface, which will be received on the 'requires' side. This will set
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the `{relation_name}.available`.
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7. If either side changes 'their' data (e.g. the data they set on the
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interface), then the receiving side will set the `{relation_name}.changed`
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state. IF the consuming charm uses the `...changed` state, it MUST remove
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it as otherwise it will not 'receive' it again.
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The important points are:
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- the `...available` state indicates the _first_ time that the data from the
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_other_ side of the interface.
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- the `...changed` state indicates the _next_ and subsequent times that data
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from the _other_ side has changed. This may not be important to the
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subordinate, but Manila will use this to rewrite the configuration files.
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- If the subordinate consumes the `...changed` state, then it must remove it
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at the end of processing, so that it can 'see' it the next time it is set.
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# metadata
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To consume this interface in your charm or layer, add the following to
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`layer.yaml`:
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```yaml
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includes: ['interface:manila-plugin']
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```
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and add a provides interface of type `manila` to your charm or layers
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`metadata.yaml`:
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```yaml
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provides:
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manila:
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interface: manila-plugin
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scope: container
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```
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Please see the example 'Manila generic backend' charm for an example of how to
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author a manila backend configuration charm.
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# Bugs
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Please report bugs on
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[Launchpad](https://bugs.launchpad.net/openstack-charms/+filebug).
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For development questions please refer to the OpenStack
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[Charm Guide](https://github.com/openstack/charm-guide).
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