New containers are autoscaling successfully now. An outdated docker agent on an autoscaling group caused duplicate host mappings, leading one target group to fail health checks, which caused the minority of the tasks in the autoscaling cluster to continually restart. If requests were routed to the healthy tasks, experience was normal. But if traffic was routed to one of these “unhealthy” tasks it only had 5 minutes that it would work – hence the sporadic success or failure of requests.
A breaking API change to Docker required updating the ECS agents from 1.55.1 to 1.55.3. Once upgrade was completed, autoscaling and host port mapping worked correctly.
