[Buildbot] #3395: document what is working with multi master in 0.9

[Buildbot trac]

#3395: document what is working with multi master in 0.9
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Reporter:  tardyp       |      Owner:
    Type:  enhancement  |     Status:  new
Priority:  major        |  Milestone:  0.9.0
 Version:  master       |   Keywords:
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 basically rephrase this and put it in the documentation

 A simple way to say it is by adding the concept of symetrics and
 asymetrics multimaster (like there is SMP and AMP for multi core CPUs)

 Symetric multimaster is when each master share the exact same
 configuration. They run the same builders, same schedulers, same
 everything, the only difference is that slaves are connected evenly
 between the masters (by any means (e.g. DNS loadbalancing, etc)) Symetric
 multimaster is good to use to scale buildbot horizontally.

 Asymetric multimaster is when each master have different configuration.
 Each master may have a specific responsability (e.g schedulers, set of
 builder, UI). This was more how you did in 0.8, also because of its own
 technical limitations. A nice feature of asymetric multimaster is that you
 can have the UI only handled by some masters.

 Separating the UI from the controlling will greatly help in the
 performance of the UI, because badly written BuildSteps? can stall the
 reactor for several seconds.

 asymetric multimaster is a more difficult goal to achieve, even if I
 understand the need, this should not block nine release

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Ticket URL: <http://trac.buildbot.net/ticket/3395>
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