Amazon ECS Service Discovery makes it possible for an ECS service to automatically register itself with a predictable and friendly DNS name in Amazon Route 53, for example backend.corp
However, assuming the use case of a web based app, host is not enough to communicate with service - also port number is required, especially when using dynamic port allocation on host(fixed container port is mapped to random host port)
How to manage dynamic port allocation with ECS Service Discovery? Sure, it is possible to use well-knows ports, but is limits number of hosts docker image can be run on.
ECS Service Discovery will register an SRV record for each task that is a combination of the Container Name and the Port (See Service Discovery Considerations). You can query these values to find the list of containers to which you can connect.
Update:
How you query DNS will be very dependant on your specific project, and the language and framework involved. In Java, for example, you'd use JNDI, in python you could use the dnspython library, and node, you'd probably use the built in dns module.