obtain storage path in charm container by storage name

I would like to be able to obtain the mounted storage location in a charm container, by storage name.

For example:

storage:
  logs:
    type: filesystem
    # specifying location on the charm container is optional
    # when unspecified, defaults to /var/lib/juju/storage/<name>/<num>

From charm code, I would like to be able to do something like “get_storage_path(“logs”)”.

One option is to increase the scope of self.meta from metadata.yaml to a broader definition. (self.meta.storages["logs"].location in this case would be None.)

[pengale]

The storage paths for some clouds are deterministic, but I don’t believe that they are guaranteed to be so in the future. AFAIK, the path being deterministic for sidecar charms is a consequence of the current implementation, and not necessarily an intentionally supported feature.

It’s safest to get the path to the storage at runtime, as close to the code that needs it as possible. The lookup is cheap, in terms of CPU resources, and the call is a one liner, so it should do no harm to require charms to do so.

If there’s a circumstance where a charm absolutely cannot get the storage path at the time that it needs it with things as they are currently written, we can re-open and investigate this issue. I believe that it should remain closed for now, however.

[pengale]

Just wanted to drop a quick note here: I think this is a good idea, and I’ve proposed fixing up location as part of the general update we’re doing to support metadata v2. Will update when/if plans get more concrete.