Availability zone support

[John Meinel]

...


> 2) If you have 2 services, you likely would rather them on the same AZ
>> rather than spread across different AZ because of the different cost of
>> network bandwidth. How do we manage multiple services? Do we just use a
>> strictly deterministic ordering? (always sort the AZ names, round robin
>> starting with the first one?)
>>
>
> It's non-deterministic. Pseudo-random choice of the least populous AZs for
> the distribution group.
>
> As for cost: this is why we have the placement directives. We default to
> spreading, but enable users to control placement if necessary.
>

So default behavior matters. I feel that sharing AZ across services by
default would probably give a better user experience. (yes units of a given
service need to be spread for proper HA, but between them it probably
doesn't matter because if one is dead the group is dead.)

I'm curious how the behavior is different from existing use. If we have
always just had each service randomly distributed it probably doesn't
matter.
John
=:->
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