mapbox/as-replace-instances — pull request #11 by ianshward (2014-09-03 19:56:36+00:00)
Title: Check for balanced AZ usage during cycle

Deals with the following scenario:

- During cycle, new capacity is all added to only 1 of 3 AZs
- After cycle completes, autoscaling rebalances
- Instances terminated during rebalance may terminate before new, balanced instances are in ELB

Therefore, check for certain level of balance across all availability zones before terminating obsolete instances.