[users at bb.net] Anotheranecdote from the multi-master trenches.

Neil Gilmore ngilmore at grammatech.com
Thu Dec 8 21:33:56 UTC 2016

Hi Pierre,

Thanks for the specifics. If it comes up again, I'll have a look in the 
places you describe.

It's slightly possible that this might have happened during a 
reconfiguration, though unlikely. I'm stll trying to train the users to 
use my supplied script to reconfigure, as it does a checkconfig and 
reconfigures all 4 masters.

I think a problem during the health-check period is much more likely. 
Though none of the masters crashed, it seems more likely that some 
network problem might have caused it to appear so. Next, time, I'll try 
the reconfig first. In this case, restarting wasn't a problem. If 
nothing else, it corrected some of the non-reconfigurable scheduler 
troubles, if only temporarily.

Neil Gilmore

On 12/8/2016 2:25 PM, Pierre Tardy wrote:
> Hi Neil,
> Thanks for the detailed report. I see few chances that the symptoms 
> you are describing could be explained by a failure of the multi-master 
> messaging.
> If the data api showed the builders that means that the builders were 
> seen to be attached to 0 masters.
> There is a "show old builders" checkbox that could have confirm that. 
> An builder is considered "old" when it has no master.
> The builders REST api has a masterids attribute that will tell that.
> There are several action that will make the list of builders of a 
> given master go to 0
> - during a reconfiguration. The BotMaster service will setup the new 
> list of builders to the database (they could go to 0 if misconfiguration)
> - at master shutdown, the master will set itself inactive, and 
> unregisters from all its builders.
> - After the master health-check period. each master has a timestamp 
> which a needs to update regularly in the database to inform other 
> masters that he his still alive. During that heartbeat callback, the 
> master will also check for other masters if they have correctly 
> updated their own timestamp. If they didn't for the previous 10 
> minutes, this means that they somehow crashed without telling, so the 
> first detecting master will mark the quiet master to be disconnected. 
> In you case, this could be explaining the behaviour. Maybe there was a 
> time were the consumer and procucers masters were unavailable, blocked 
> or off-network. The third master marked them away, but the 2 then went 
> back, but did not figure out they were marked disconnected, but still 
> continued to take buildrequests. I think this is a design bug that we 
> need to fixed. A single reconfig would have fixed the situation (no 
> need for restart)
> In any case I would expect that the twisted.log may tell you some 
> stuff. Either you would get some exceptions during a reconfiguration 
> or something. Or you may get a period of time with suspicious 
> activity, which could explain a miss of the heartbeat timer.
> Let us know if you reproduce the problem again and if these advices 
> helped you better understand the problem.
> regards,
> Pierre
> Le jeu. 8 déc. 2016 à 17:45, Neil Gilmore <ngilmore at grammatech.com 
> <mailto:ngilmore at grammatech.com>> a écrit :
>     Hi everyone.
>     First, a bit of good news. My current top priority is to make the
>     schedulers reconfigurable. Not conceptually difficult, but I wasn't
>     well-versed in Python argument passing (which figures prominently in
>     this), so I've had a couple aborted tries on that score. I think I've
>     got all that sorted out for now. It's just biting us way too badly to
>     not be able to reconfigure schedulers.
>     Now, the anecdote. As you may remember, we're running 4 masters. 1
>     just
>     has the UI and force schedulers. 1 has our overall logging system. The
>     other 2 are split between producing builds, and consuming them for
>     tests.
>     Sometime between when I left yesterday and when the test lead looked
>     this morning, the UI stopped displaying the builders for the producer
>     and consumer masters. Looking at all the masters, they were
>     running, and
>     I didn't immediately see anything suspicious in the logs. Looking
>     at the
>     data api, I could see all the builders and workers. The workers all
>     showed connected_to being valid, but only the logging workers showed
>     anything in configured_on. I restarted our UI master and that didn't
>     help. Restarting the producer and consumer seems to have solved the
>     problem. I can see the builders in the UI, and looking at the
>     workers in
>     the data API, I see that most appear to have configured_on set. I have
>     no idea what actually happened. My wild conjecture is that the
>     inter-master communication got screwed up somehow. Either that or they
>     lost connection to the database (less likely, I think. Postgres is
>     pretty stable that way.).
>     Neil Gilmore
>     grammatech.com <http://grammatech.com>
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