Get rabbit ready before we start workers

[nedbat]

This is the same change as in #2871, but also applies it to the devstack
and fullstack vagrant plays.

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[nedbat]

@feanil @jibsheet This is the same as #2871, with the change made in more places. Do I need rabbit in devstack if edxapp doesn't have worker=True?

Also, bonus points for anyone who can explain why this is happening now. It feels like we are leaking the future into the Dogwood past, and we don't know where.

I'll be cherry-picking this commit onto dogwood.rc when approved.

[feanil]

The error looks to be un-related to this change. 👍

[jibsheet]

It looks like in devstacks, you can leave the order alone, since we only install rabbit for ecom_worker
caebe2d
Otherwise 👍

[feanil]

@jibsheet there is also an error with the edxapp workers that is being reported on the mailing list and in slack that should be adressed by moving the rabbit role up. It seems like there is a chance for occassional deadlock when the workers come up and can't connect to rabbit.

[jibsheet]

@feanil on devstack? Devstack workers are in process I thought.

[nedbat]

@jibsheet I wondered about the need for the re-ordering on devstack, but it still seems like a good idea to install lower-level services (like rabbit) before upper-level, and to have devstack and fullstack be similar where possible.