# Amazon ECS service throttle logic
<a name="service-throttle-logic"></a>

The Amazon ECS service scheduler includes protective logic that throttles task launches when tasks repeatedly fail to start. This helps prevent unnecessary resource consumption and reduces costs.

When tasks in a service fail to transition from `PENDING` to `RUNNING` state and instead move directly to `STOPPED`, the scheduler:
+ Incrementally increases the time between restart attempts
+ Continues increasing delays up to a maximum of 27 minutes between attempts
+ Generates a service event message to notify you of the issue

**Note**  
The maximum delay period of 27 minutes may change in future updates.

When throttling is activated, you receive this service event message:

```
(service service-name) is unable to consistently start tasks successfully.
```

Important characteristics of the throttle logic:
+ Services continue retry attempts indefinitely
+ The only modification is the increased time between restarts
+ There are no user-configurable parameters

## Resolving throttling issues
<a name="resolving-throttling"></a>

To resolve throttling, you can:
+ Update the service to use a new task definition, which immediately returns the service to normal, non-throttled operation. For more information, see [Updating an Amazon ECS service](update-service-console-v2.md).
+ Address the underlying cause of the task failures.

Common causes of task failures that trigger throttling include:
+ Insufficient cluster resources (ports, memory, or CPU)
  + Indicated by an [insufficient resource service event message](service-event-messages-list.md#service-event-messages-1)
+ Container image pull failures
  + Can be caused by invalid image names, tags, or insufficient permissions
  + Results in `CannotPullContainerError` in [Viewing Amazon ECS stopped task errors](stopped-task-errors.md)
+ Insufficient disk space
  + Results in `CannotCreateContainerError` in [stopped task errors](stopped-task-errors.md)
  + For resolution steps, see [Troubleshoot the Docker `API error (500): devmapper` in Amazon ECS](CannotCreateContainerError.md)

**Important**  
The following scenarios do NOT trigger throttle logic:  
Tasks that stop after reaching `RUNNING` state
Tasks stopped due to failed Elastic Load Balancing health checks
Tasks where the container command exits with a non-zero code after reaching `RUNNING` state