CI hates juju, maybe the feelings are mutual

[John Meinel]

So Juju would certainly let you run an older binary, and it would, indeed,
switch to that binary.
What it has *never* done is back out any actual changes to your
environment. So any upgrade that changed any data on disk (the contents of
agent.conf, a cert, something like that) would remain in the upgraded
content.
And explicitly 1.16 => 1.18 changed agent.conf in a way that old agents
would fail to read the new agent.conf file.
And we had a bug where upgrading from 1.16 => 1.18 would succeed, but then
immediately try to revert back to 1.16 (because 1.18 prefers to upgrade in
an ordered fashion, with machines upgrading before units, so if the unit
upgraded first, it would try to downgrade back before proceeding.)

I would be ok with allowing downgrades within a PATCH level, but I think it
still holds true that downgrades are very untested, and downgrading across
a MINOR version is almost definitely always going to do something bad.

That said, I think for CI getting bootstrap to target an explicit version
is far better than bootstrapping to the latest trunk, and then downgrading.
I would be willing to compromise in the short term by adjusting the "refuse
to downgrade" to only refuse to change Major.Minor versions. It still fixes
the existing bug, and would let CI continue.

John
=:->



On Thu, Apr 10, 2014 at 6:45 PM, Aaron Bentley
<aaron.bentley at canonical.com>wrote:

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> On 14-04-10 05:41 AM, John Meinel wrote:
> > Well you used to be able to request a downgrade, but it never
> > actually worked... :)o
>
> Could you explain that further?
>
> We've done thousands of downgrades and juju reported that it had
> switched the agent to the requested version.
>
> We first implemented downgrading in November or so.  Are you saying
> Juju has been lying the whole time?
>
> Aaron
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