The port number on the container instance to reserve for your container. You can specify a non-reserved host port for your container port mapping, or you can omit the hostPort (or set it to 0) while specifying a containerPort and your container automatically receives a port in the ephemeral port range for your container instance operating system and Docker version.
The default ephemeral port range is 49153 to 65535, and this range is used for Docker versions prior to 1.6.0. For Docker version 1.6.0 and later, the Docker daemon tries to read the ephemeral port range from /proc/sys/net/ipv4/ip_local_port_range; if this kernel parameter is unavailable, the default ephemeral port range is used. You should not attempt to specify a host port in the ephemeral port range, because these are reserved for automatic assignment. In general, ports below 32768 are outside of the ephemeral port range.
The default reserved ports are 22 for SSH, the Docker ports 2375 and 2376, and the Amazon ECS container agent port 51678. Any host port that was previously specified in a running task is also reserved while the task is running (after a task stops, the host port is released).The current reserved ports are displayed in the remainingResources of DescribeContainerInstances output, and a container instance may have up to 100 reserved ports at a time, including the default reserved ports (automatically assigned ports do not count toward the 100 reserved ports limit).