AWS – ECS Keeps Recreating Docker Container

AWS ECS Logo

Today was a strange day. I’ve launched a new version of my docker image within an ECS cluster, which usually worked fine. However, today my container always got recreated every 5 minutes for no reason.

ecs_keeps_recreating_containers

The new docker image that I have pushed to the repository had no significant changes, except a redirect from non-SSL ( 80 ) to SSL ( 443 ) for all loaded virtual hosts. So, when I had a look at the processes, everything looked fine. There was nothing that could put the container into an unhealthy status.

Even the log output of the docker container didn’t show any error. After a little bit of research, I ended up on the following AWS developer guide page https://docs.aws.amazon.com/AmazonECS/latest/developerguide/update-service.html

It was not exactly what I was looking for, but it pretty much explained the problem I had. One of my colleagues said I should maybe have a look at the health checks of the load balancer.

Indeed, when I had a look at the settings in EC2 > Load Balancing > Target Groups > Health Checks the health check expected a success code 200 instead of 301 on port 80. Because of that, the container has been marked unhealthy every 5 minutes.

aws_ec2_load_balancer_health_checks

I hope this will point someone in the right direction.

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