Application Load Balancer

Your Amazon ECS service can optionally be configured to use Elastic Load Balancing to distribute traffic evenly across the tasks in your service.

Elastic Load Balancing supports the following types of load balancers: Application Load Balancers, Network Load Balancers, and Classic Load Balancers, and Amazon ECS services can use either type of load balancer. Application Load Balancers are used to route HTTP/HTTPS (or Layer 7) traffic. Network Load Balancers and Classic Load Balancers are used to route TCP (or Layer 4) traffic. For more information, see Load Balancer Types.

Application Load Balancers offer several features that make them attractive for use with Amazon ECS services:

• Application Load Balancers allow containers to use dynamic host port mapping (so that multiple tasks from the same service are allowed per container instance).
• Application Load Balancers support path-based routing and priority rules (so that multiple services can use the same listener port on a single Application Load Balancer).

We recommend that you use Application Load Balancers for your Amazon ECS services so that you can take advantage of these latest features, unless your service requires a feature that is only available with Network Load Balancers or Classic Load Balancers. For more information about Elastic Load Balancing and the differences between the load balancer types, see the Elastic Load Balancing User Guide.

Reference details : 

https://docs.aws.amazon.com/AmazonECS/latest/developerguide/load-balancer-types.html

https://docs.aws.amazon.com/AmazonECS/latest/developerguide/service-load-balancing.html

https://docs.aws.amazon.com/elasticloadbalancing/latest/userguide/