Review the ECS task or service definition for the portMappings section. Check the value of hostPort in each container's configuration:

• If hostPort is either blank or set to 0, multiple tasks can be placed on the same container instance without issue.

• If hostPort equals containerPort, each task will require a unique host port assignment. This results in one task per node, preventing bin packing and triggering unnecessary scale-ups.

Example configuration causing underutilization

1. Update the task definition so hostPort is left blank or set to 0 unless a specific port binding to the host is required for your use case.

2. Verify all containers in the task definition because multiple containers may define separate portMappings.

Outcome

Adjusting the hostPort configuration enables ECS to bin pack tasks efficiently, reducing the number of container instances and improving cost optimization.