ECS unhealthy task is stopped but replacing task is launched after 60+ minutes

The delay in launching the replacement task in Amazon ECS could be due to several reasons. Here are some potential reasons and troubleshooting tips:

1. Resource Shortages: If your cluster doesn't have enough resources (CPU, Memory, etc.) to launch a new task, ECS will not be able to start the replacement task until resources become available. This could happen if there are other tasks running in the cluster that are consuming a lot of resources. You can monitor your cluster's resource utilization in the ECS console to see if this might be the issue.

2. Task Placement Constraints or Strategies: If you have task placement constraints or strategies that cannot be satisfied, this could also delay the launch of the replacement task. For example, if you have a constraint that the task must be placed on a specific type of instance, and no such instances are available, the task launch could be delayed.

3. Service Throttling: AWS has rate limiting in place to protect the service from being overwhelmed. If you've been starting and stopping tasks very frequently, you might hit these limits, which could cause delays. You can review the service quotas (previously known as limits) in the ECS documentation and request an increase if necessary.

4. Task Definition Issues: If there are issues with the task definition, such as problems with the Docker image or the container parameters, ECS might not be able to launch the task. Check the task definition to make sure everything is correct.

5. Issues with ECS Service: Sometimes, there could be delays due to issues on the ECS service side. Check the AWS Service Health Dashboard to see if there are any ongoing issues with ECS in your region.

To troubleshoot this further, you can look at the ECS service events in the AWS Management Console. These events can give you more information about why the task is not being started. If you have CloudWatch Logs set up for your tasks, you can also check those logs for any error messages or other information that might help you diagnose the problem.

Some other topics to check:

• Are you using the Amazon ECS-optimized AMI or a self-baked one?
• If a custom ECS AMI I would check the /etc/ecs.config file for custom timeouts that might delay the stop or start of the task https://github.com/aws/amazon-ecs-agent/blob/master/README.md (ECS_CONTAINER_STOP_TIMEOUT for example).
• What the Events are telling you?
• Check the ecs-agent logs if you have them enabled. As well syslog
• I would also check the instance metrics for CPU, Network I/O and if you have CloudWatch Agent configured to send memory and swap data check the memory stats.

Thanks!

I have found three refs that maybe related to your problem

https://stackoverflow.com/questions/44436048/amazon-aws-ecs-task-delay https://docs.aws.amazon.com/AmazonECS/latest/bestpracticesguide/task.html https://repost.aws/knowledge-center/ecs-tasks-container-exit-issues

as a summary

If your task starts on a container instance that doesn't have your base image already downloaded, this can result in a delay. You can help alleviate this by pre-loading your instances, improving the networking throughput of your instances, or reducing your image size.

If you are running Amazon ECS on Amazon EC2, you can configure the Amazon ECS container agent to cache previously used container images to reduce image pull-time for subsequent launches. Using the binpack placement strategy can further enhance this effect by increasing task density in your container instances​

Rhe choice of network mode and instance type can significantly influence task launch latency. For instance, the awsvpc network mode may add several seconds of overhead to your task launches, and choosing an optimal instance type based on your task's resource reservation can help to better utilize the instance's resources​.

Using the Amazon ECS service scheduler to concurrently launch services can speed up the overall deployment process. Designing your applications as smaller services with fewer tasks rather than a large service with a large number of tasks can result in faster deployment speed​

To further troubleshoot this issue, check the diagnostic information in the service event log, the stopped tasks for errors, and your application logs for application issues. If the awslogs log driver is configured in your task definition, check the logs in CloudWatch Logs​. You can also consider tracking your task launch lifecycle to find optimization opportunities and understand how your application is contributing to the total launch time.

Leandro,

You can allow your application the opportunity to recover from the high CPU usage burst by adjusting the health check settings in the task definition as well as in the service configuration. Please see the 3 links below.

[1] https://docs.aws.amazon.com/AmazonECS/latest/bestpracticesguide/load-balancer-healthcheck.html

[2] https://docs.aws.amazon.com/AmazonECS/latest/userguide/task_definition_parameters.html#container_definition_healthcheck

[3] https://docs.aws.amazon.com/AmazonECS/latest/userguide/service_definition_parameters.html#sd-deploymentconfiguration