Rolling Deployments

The default deployment strategy replaces tasks gradually with the new revision.

By default ECS uses a rolling update. When you point a service at a new task-definition revision, ECS starts new tasks and stops old ones a few at a time.

Controlling the roll

minimumHealthyPercent — how many tasks must stay running during the deploy.
maximumPercent — how many extra tasks may run at once.

For example 100/200 keeps full capacity while doubling briefly; 50/100 deploys in place with less spare compute.

Example

# Register a new revision, then trigger a rolling update
aws ecs update-service \
  --cluster prod --service web \
  --task-definition web:8 \
  --deployment-configuration 'minimumHealthyPercent=100,maximumPercent=200'

When to use it

A team deploys a new API version by registering a new task definition revision and updating the service, letting ECS replace tasks gradually with zero downtime.
An SRE sets minimumHealthyPercent to 100 and maximumPercent to 200 so ECS always brings up new tasks before terminating old ones during a deployment.
An engineer enables the deployment circuit breaker so ECS automatically rolls back to the previous revision when more than 50% of new tasks fail to reach a healthy state.

More examples

Deploy New Revision via Service Update

Points the service at task definition revision 8 and forces a rolling replacement of all existing tasks with the new version.

aws ecs update-service \
  --cluster prod \
  --service api \
  --task-definition api:8 \
  --force-new-deployment

Set Deployment Configuration

Configures the service to keep 100% of healthy tasks running during deployment by doubling capacity temporarily — true zero-downtime rolling update.

aws ecs update-service \
  --cluster prod \
  --service api \
  --deployment-configuration \
    'minimumHealthyPercent=100,maximumPercent=200'

Enable Deployment Circuit Breaker

Enables the deployment circuit breaker with automatic rollback so ECS reverts to the last stable revision if the new deployment fails health checks.

aws ecs update-service \
  --cluster prod \
  --service api \
  --deployment-configuration \
    'deploymentCircuitBreaker={enable=true,rollback=true}'

Discussion

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