A too-long application name leaves charm stuck installing agent

[Adam Israel]

Using libjuju to drive Juju 2.2.6, I've found that it's possible to deploy a charm that will always get stuck during 'installing agent' by specifying an application that is too long.

Step to recreate:

juju deploy mysql jujud-unit-pytest-bb-ai-bh-bd-ag-dc-ping-pong-ns-default-pytest-bb-ai-bh-bd-ag-dc-ping-pong-ns-ping-vnf-b-b-0

Observed behaviour:
`juju status` simply shows that the charm is 'installing agent' and does not change regardless of how long it's let run.

`juju debug-log` shows this recurring repeatedly:
machine-0: 13:40:34 ERROR juju.service.systemd service "jujud-unit-pytest-bb-ai-bh-bd-ag-dc-ping-pong-ns-default-pytest-bb-ai-bh-bd-ag-dc-ping-pong-ns-ping-vnf-b-b-0" failed to start: application jujud-unit-pytest-bb-ai-bh-bd-ag-dc-ping-pong-ns-default-pytest-bb-ai-bh-bd-
ag-dc-ping-pong-ns-ping-vnf-b-b-0 not found

Expected behaviour:

The deploying charm should enter an error state so that the operator (either a user or automaton driving libjuju) knows that deployment has failed (and why)

[Adam Israel (aisrael)]

It looks like the max name length is 51 characters. I can deploy an application named that long, but as soon as it hits 52 or above it triggers the above behavior.

[Tim Penhey (thumper)]

Looks like there is a lenght limit on systemd service names of 64 characters.

We have "jujud-unit-" + app name + "-0" (for the first unit)

With a 51 character limit app name, we hit 64 characters for the service name (until you add the eleventh unit).

Juju should impose a resonable name limit length on applications.

[Richard Harding (rharding)]

As the naming issue is an implementation detail of how things are named for the systemd bits is it important to force that onto the charm developer? Since the charm names are defaulted as application names this could be seriously backward compatible and really means this needs to be enforced upstream on the charm command and the charmstore itself.

Ideally juju would handle the naming here itself and leave things as the user expressed them everywhere else.

[Witold Krecicki (wpk)]

https://github.com/juju/juju/pull/8060

[Junien F (axino)]

Proposed a better fix in https://github.com/juju/juju/pull/8336 - the root cause is not a name length limit in systemd, but systemd ellipsizing unit names

It is also totally backwards-compatible