Scheduling Amazon ECS Tasks
Amazon Elastic Container Service (Amazon ECS) is a shared state, optimistic concurrency system that provides flexible scheduling capabilities for your tasks and containers. The Amazon ECS schedulers leverage the same cluster state information provided by the Amazon ECS API to make appropriate placement decisions.
Amazon ECS provides a service scheduler (for long-running tasks and applications), the ability to run tasks manually (for batch jobs or single run tasks), with Amazon ECS placing tasks on your cluster for you. You can specify task placement strategies and constraints that allow you to run tasks in the configuration you choose, such as spread out across Availability Zones. It is also possible to integrate with custom or third-party schedulers.
Service Scheduler
The service scheduler is ideally suited for long running stateless services and applications. The service scheduler ensures that the specified number of tasks are constantly running and reschedules tasks when a task fails (for example, if the underlying infrastructure fails for some reason). The service scheduler optionally also makes sure that tasks are registered against an Elastic Load Balancing load balancer. You can update your services that are maintained by the service scheduler, such as deploying a new task definition, or changing the running number of desired tasks. By default, the service scheduler spreads tasks across Availability Zones, but you can use task placement strategies and constraints to customize task placement decisions. For more information, see Services.
Manually Running Tasks
The RunTask action is ideally suited for processes such as batch jobs
that perform work and then stop. For example, you could have a process call
RunTask when work comes into a queue. The task pulls work from the
queue, performs the work, and then exits. Using RunTask, you can allow the
default task placement strategy to distribute tasks randomly across your cluster,
which
minimizes the chances that a single instance gets a disproportionate number of tasks.
Alternatively, you can use RunTask to customize how the scheduler places
tasks using task placement strategies and constraints. For more information, see Running Tasks and RunTask in the
Amazon Elastic Container Service API Reference.
Running Tasks on a cron-like Schedule
If you have tasks to run at set intervals in your cluster, such as a backup operation
or a log scan, you can use the Amazon ECS console to create a CloudWatch Events rule
that runs one or
more tasks in your cluster at specified times. Your scheduled event rule can be set
to
either a specific interval (run every N minutes, hours, or
days), or for more complicated scheduling, you can use a cron expression.
For more information, see Scheduled Tasks (cron).
Custom Schedulers
Amazon ECS allows you to create your own schedulers that meet the needs of your business, or to leverage third party schedulers. Blox is an open- source project that gives you more control over how your containerized applications run on Amazon ECS. It enables you to build schedulers and integrate third-party schedulers with Amazon ECS while leveraging Amazon ECS to fully manage and scale your clusters. Custom schedulers use the StartTask API operation to place tasks on specific container instances within your cluster. For more information, see StartTask in the Amazon Elastic Container Service API Reference.
Note
Custom schedulers are only compatible with tasks using the EC2 launch type. If you are using the Fargate launch type for your tasks, the StartTask API does not work.
Task Placement
The RunTask and CreateService actions enable you to specify
task placement constraints and task placement strategies to customize how Amazon ECS
places
your tasks. For more information, see Amazon ECS Task Placement.
