Which statement about port mapping is true?

The choice regarding port collision errors is accurate because when two containers are configured to expose the same external port on the host machine, they will indeed conflict with each other. This results in a scenario where the host cannot determine which container's service to direct traffic to, leading to port collision errors. Consequently, only one container can listen to a specific port on the host at a time.

Understanding this concept helps in proper networking and service configuration within Docker. It emphasizes the need for unique port assignments on the host for each running container that exposes a port, ensuring seamless traffic management and preventing access issues among services that may need to communicate reliably over the same network interface.

Other choices present different aspects of Docker functionality: one suggests a fixed mapping of host and container ports, which is not necessary, as ports can be mapped flexibly. Another implies a single port mapping per service, which doesn't account for services that might need multiple ports. Lastly, the notion that all ports must be externalized for security lacks flexibility; security configurations can vary based on application requirements and typically allow for internal communication without exposing every port. Thus, understanding how port mappings work is crucial for effective Docker container management.