juju unable to find revision of charm in Store for bundle overlay

[Heitor]

So far I've been unable to deploy prometheus-node-exporter as a bundle overlay.

The following bundle works and I can deploy it locally without issues:

```
$ cat slurm-addons/monitoring.yaml
applications:
  prometheus2:
    charm: prometheus2
    num_units: 1
  node-exporter:
    charm: prometheus-node-exporter
relations:
  - - prometheus2:scrape
    - node-exporter:prometheus
```

But when I use it as an overlay for another bundle, it fails:

```
$ juju deploy ./slurm-core/bundle.yaml --overlay ./slurm-core/clouds/lxd.yaml --overlay ./slurm-core/series/centos7.yaml --overlay ./slurm-core/charms/local-development.yaml --overlay ./slurm-addons/monitoring.yaml --debug

# removing lots of lines about the current model

09:41:05 INFO cmd bundlehandler.go:355 Located charm "prometheus-node-exporter" in charm-hub, channel stable
09:41:05 DEBUG juju.cmd.juju.application.deployer bundlehandler.go:309 slurmctld exists in model uses a local charm, replacing with "local:centos7/slurmctld-0"
09:41:05 DEBUG juju.cmd.juju.application.deployer bundlehandler.go:309 slurmd exists in model uses a local charm, replacing with "local:centos7/slurmd-0"
09:41:05 DEBUG juju.cmd.juju.application.deployer bundlehandler.go:309 slurmdbd exists in model uses a local charm, replacing with "local:centos7/slurmdbd-0"
09:41:05 DEBUG juju.cmd.juju.application.deployer bundlehandler.go:309 slurmrestd exists in model uses a local charm, replacing with "local:centos7/slurmrestd-0"
Executing changes:
- upload charm prometheus-node-exporter from charm-hub for series centos7 with architecture=amd64
09:41:11 DEBUG juju.api monitor.go:35 RPC connection died
ERROR cannot deploy bundle: cannot add charm "prometheus-node-exporter": revision-not-found: No revision was found in the Store.
09:41:11 DEBUG cmd supercommand.go:537 error stack:
revision-not-found: No revision was found in the Store.
/build/snapcraft-juju-35d6cf/parts/juju/src/rpc/client.go:178:
/build/snapcraft-juju-35d6cf/parts/juju/src/api/apiclient.go:1248:
/build/snapcraft-juju-35d6cf/parts/juju/src/api/charms/client.go:157:
/build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/store/store.go:44:
/build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deployer/bundlehandler.go:667: cannot add charm "prometheus-node-exporter"
/build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deployer/bundlehandler.go:539:
/build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deployer/bundlehandler.go:101:
/build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deployer/bundle.go:172: cannot deploy bundle
```

[james beedy (jamesbeedy)]

I would imagine this is happening due to issues with charmhub support for centos7. The promtheus-node-exporter supports centos7 but charmhub doesn't know what to do with it.

[Heitor (heitorpbittencourt)]

If I modify the YAML file to specify focal as the series, the overlay works:

```
applications:
  prometheus2:
    charm: prometheus2
    num_units: 1
  node-exporter:
    charm: prometheus-node-exporter
    series: focal
relations:
  - - prometheus2:scrape
    - node-exporter:prometheus
```

But does not work with CentOS7.

[Heitor (heitorpbittencourt)]

Prometheus-node-exporter charm does not have a `series` entry in the metadata.yaml

Maybe that's why is causing the issue? Charmhub interprets that as focal-only charm?

https://github.com/omnivector-solutions/charm-prometheus-node-exporter

[Simon Richardson (simonrichardson)]

So currently charmhub only supports ubuntu series, I think the error message could be improved to help with the error, but it's hard to understand what you want when the prometheus-node-exporter charm doesn't have a default series.

[Heitor (heitorpbittencourt)]

> So currently charmhub only supports ubuntu series
Is there a roadmap for charmhub to support other OSes?

> but it's hard to understand what you want when the prometheus-node-exporter charm doesn't have a default series.

according to [0], the `series` entry in the metadata is going to be deprecated. I though Charmhub already had support for the new `charmcraft.yaml` `bases` entry, but apparently it doesn't? Charmcraft requires us to specify the `bases`, having to also add `series` sounds like duplicating information, or I am missing something?

Should we always add the `series` entries then?

[0] https://discourse.charmhub.io/t/charm-metadata-v2/3674