juju upgrade-series doesn't work if the target series isn't available in distro-info on the CLIENT machine

[Alex Kavanagh]

I've been upgrading an Juju + OpenStack machine from circa 2016 where the machines all started life as Xenial.

The 'main' machine is a Xenial host, running MaaS, and the controller is also running on a Xenial VM.

The controller and model have been upgraded from 2.3.2 -> 2.8.10 (with the intermediary steps).
The client is 2.8.11 on Xenial.

Upon issuing "juju upgrade-series" juju responded as:

$ juju upgrade-series 3/lxd/0 prepare focal
ERROR "focal" is an unsupported series

After many, many hours of checking the controller, images, charms' metadata.yaml on the machine, eventually, it was suggested that distro-info on the CLIENT machine may not have focal info.

Sure enough, it didn't, as the Xenial has been updated in a while.

So I "apt update && apt install distro-info" and focal appeared in the /usr/share/distro-into/ubuntu.csv file as expected.

I then issued the upgrade-series command again, and:

$ juju upgrade-series 3/lxd/0 prepare focal
WARNING: This command will mark machine "3/lxd/0" as being upgraded to series "focal".
This operation cannot be reverted or canceled once started.
Units running on the machine will also be upgraded. These units include:
  rabbitmq-server/5
  nrpe/43

Leadership for the following applications will be pinned and not
subject to change until the "complete" command is run:
  nrpe
  rabbitmq-server

Continue [y/N]?

---

So a few observations here:

1. client details of focal in distro-info were required? To series-upgrade a machine on a server in a distant cloud. Obviously, that's a bug.
2. Would it have worked if I was on say, CentOS, a Mac or Arch?
3. The error message is extremely unhelpful. Adding verbosity does nothing to help. There is no indication as to whether this was a charm issue, an image issue, an version issue, etc. More verbose and informative error messages are needed here, please.

[Simon Richardson (simonrichardson)]

So a few observations; I believe we're attempting to fail early, but in order to fail early we need valid up-to-date information. The problem is we don't know if you have the up-to-date information and we don't tell uses of the juju client that they'll require an up-to-date distro-info via apt.

I suspect we can skip the local validation check in the CLI so that the actual check is done server-side.

[Simon Richardson (simonrichardson)]

There is a workaround for 2.8 and we'll fix this with the upgrade-series work that's going to take place in the 2.9 work[1]

 1. https://docs.google.com/document/d/110SphNniTTnAqmW5sTrHZRVgTDiizSuOvMU2WM_0-2A

[Simon Richardson (simonrichardson)]

Updated documentation about the client prerequisites and the need for distro-info[1]

1. https://discourse.charmhub.io/t/client/1083