How the ECS Scheduler Places & Replaces Tasks
~10 min read
What actually happens inside ECS when a service's desired count changes or a task fails.
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Key points
- •The scheduler continuously reconciles actual task count toward desired task count
- •Placement strategy 'spread' across AZs is the default resilience pattern on EC2 launch type
- •A failed health check triggers deregistration + termination + replacement, usually within a minute
- •Desired count should always account for at least N+1 capacity so one task failure never drops below traffic-serving minimum