Instance Maintenance Policy & Refresh Behavior
~8 min read
How an Auto Scaling Group replaces instances during a rolling update without dropping below minimum healthy capacity.
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Key points
- •Instance maintenance policy controls min/max healthy percentage bounds during instance replacement
- •A minimum healthy percentage below 100% allows old instances to be terminated before all new ones are ready, trading brief reduced capacity for a faster/cheaper rollout
- •A maximum healthy percentage above 100% allows new instances to launch before old ones are terminated, avoiding any capacity dip at the cost of briefly running extra instances
- •Conceptually parallel to ECS's rolling update deployment strategy, applied to raw EC2 instances instead of containerized tasks