Previously, the number of tasks in awsvpc network mode that could be run on an instance was limited by the number of available Elastic Network Interfaces (ENIs) on the instance; those ENIs could be used by ECS tasks or by other processes outside of ECS. As a result, the number of tasks that could be placed on EC2 instances often was constrained despite there being ample vCPU and memory available for additional containers to utilize. Now, you have access to an increased number of ENIs for use exclusively by tasks in awsvpc networking mode for select instance types. The increase is anywhere from 3 to 8 times the previous limits, depending on the instance type.
The improved ENI limits are available in all regions where ECS is available. Please visit the AWS region table to see where Amazon ECS is available.