Running upgrade steps for units

[Menno Smits]

On 16 September 2015 at 08:41, Tim Penhey <tim.penhey at canonical.com> wrote:

> On 15/09/15 19:38, William Reade wrote:
> > Having the machine agent run unit agent upgrade steps would be a Bad
> > Thing -- the unit agents are still actively running the old code at that
> > point. Stopping the unit agents and managing the upgrade purely from the
> > machine would be ok; but it feels like a lot of effort for very little
> > payoff, so I'm most inclined to WONTFIX it and spend the energy on agent
> > consolidation instead.
>
> This still leaves us with the problem of the two upgrade steps that were
> written to update the uniter state file, and how to handle this.
>

If the work that these upgrade steps did is fairly trivial we could have
the unit agents run a function which does the upgrade work as it comes up,
before workers are started. This might be an acceptable solution if we're
going to merge machine and unit agents soon[1] anyway.

I had thought it might be reasonably easy to get the upgrade machinery
working within the unit agent but now that I've looked at the code I can
see that it's a fairly major undertaking (to do it Right at least).

- Menno


[1] FSVO "soon"
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