8

I just noticed that all of our EC2 instances are in zone us-west-2b, but our Multi-AZ RDS instance is in us-west-2a.

Performance-wise everything seems to be okay, and it will be a hassle to "move" the instances to one place since you have to stop and re-create them all. However if either of the two zones goes down when we will have some downtime; if everything is in one zone then at least we have a higher chance of not being in the zone that has downtime...

Is this something worth fixing, or am I over-thinking it?

(I was about to purchase some EC2 Reserved Instances, which are tied to specific AZs, so I wanted to make sure before going through with it)

Thanks!

3
  • It's Multi-AZ. The primary may be in us-west-2a right now, but that can change at any time. If the AZ it's in goes down, it's supposed to switch to another one automatically, so having your EC2s spread out should help with uptime rather than having them all go down if us-west-2b fails.
    – ceejayoz
    May 29, 2014 at 19:55
  • So, don't worry about it then?
    – DOOManiac
    May 29, 2014 at 20:40
  • Don't worry about the RDS, and consider moving some of the instances into another AZ so you can be multi-AZ on that front as well.
    – ceejayoz
    May 29, 2014 at 20:43

1 Answer 1

9

The Multi-AZ nature of your RDS means it may not always be in that AZ - they can move around. In the event of a failure of its current primary AZ, it'll fail over into another one automatically. As such, it doesn't make sense to move EC2 instances around to follow it when it could move away on its own.

You should consider, however, moving some of your EC2 instances into another AZ (maybe from us-west-2b to us-west-2a) so that if an AZ goes down you'll have both the RDS and some of your EC2 instances still up and running.

1
  • 5
    Does this mean you're paying the "region data transfer - in/out/between EC2 AZs" at random (or is that only in the event of a failure)?
    – hayd
    Oct 15, 2016 at 4:55

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .