[users at bb.net] Multi-master 0.9.3 anecdotes.

[Andrej Rode]

Hi Neil,

> 2017-02-03T12:39:09-0500 [Broker,28906,10.233.216.43] worker '<name>'
> attaching from IPv4Address(TCP, '<ip>', 35642)
> 2017-02-03T12:39:09-0500 [Broker,28906,10.233.216.43] Got workerinfo
> from '<name>'
> 2017-02-03T12:39:09-0500 [-] bot attached
> 2017-02-03T12:39:09-0500 [-] worker <name> cannot attach
>         Traceback (most recent call last):
>         Failure: twisted.internet.error.AlreadyCalled: Tried to cancel
> an already-called event.

I had the same problembs but with a single-master setup. By any chance
are you using a non-default `missing_timeout` and/or `notify_on_missing`
on your workers?

For my issue I've a PR up [0] and now I can detach and  attach workers
as I like. But it is still not clear why we even run into problems here.

I figured out that attaching a worker after longer than
`missing_timeout` after a master start results in this problem on my
setup. (Default `missing_timeout` is 60 minutes.)

Cheers,
Andrej

[0] https://github.com/buildbot/buildbot/pull/2708