AWS Compute Blog

Maintaining Transport Layer Security All the Way to Your Container: Using the Network Load Balancer with Amazon ECS

This post contributed by AWS Senior Cloud Infrastructure Architect Anabell St Vincent.

Some systems or applications require Transport Layer Security (TLS) traffic from the client all the way through to the Docker container, without offloading or terminating certificates at a load balancer. Some highly time-sensitive services may require communication over TLS without any decryption and re-encryption in the communication path.

There are multiple options for this type of implementation on AWS. One option is to use a service discovery tool to implement the requirements, but that creates overhead from an implementation and management perspective. In this post, I examine the option of using Amazon Elastic Container Service (Amazon ECS) with a Network Load Balancer.

Amazon ECS is a highly scalable, high-performance service for running Docker containers on AWS. It is integrated with each of the Elastic Load Balancing load balancers offered by AWS:

  • The Classic Load Balancer supports application or network level traffic and can be used to pass through the TLS traffic when configured with TCP listeners. This approach limits the number of containers to be deployed by Amazon ECS to one per EC2 host. This approach is only available for the ECS launch type of EC2, not Fargate. This is due to Classic Load Balancer not supporting target groups, so dynamic port mapping can’t be leveraged for this type of implementation.
  • The Application Load Balancer functions at the application layer, the layer 7 of Open System Interconnection (OSI) and supports HTTP and HTTPS protocols. By operating at layer 7, the Application Load Balancer is able to route traffic based on the request path in the URL. It can also provide SSL offloading or termination of the SSL certificates for applications, by hosting the SSL certificate. The Application Load Balancer integrates well with ECS by providing the functionality of the target groups for the container instances, which allows for port mapping and targeting container groups. Port mappings allows the containers to run on different ports but still be represented by the one port configured on the ALB as part of the target group of the task.
  • The Network Load Balancer, which is a high performance, ultra-low latency load balancer that operates at layer 4. It is designed to handle tens of millions of requests per second while maintaining high throughput at ultra-low latency. Operating at layer 4 networking means that the traffic is passed onto the targets based on the IP addresses and ports as oppose to session information or cookies, as is the case with Application Load Balancers. The Network Load Balancer also supports long-lived TCP connections, which are ideal for WebSocket type of applications . Some applications communicate on TCP protocols rather than solely on HTTP and HTTPS. The Network Load Balancer provides the support to load balance between services that require protocols besides HTTP and HTTPS.

The Network Load Balancer is the best option for managing secure traffic as it provides support for TCP traffic pass through, without decrypting and then re-encrypting the traffic. Additionally, the Network Load Balancer supports target groups, which means port mapping can be used, as well as configuring the load balancer as part of the task definition for the containers.


The diagram below shows a high-level architecture with TLS traffic coming from the internet that passes through the VPC to the Network Load Balancer, then to a container without offloading or terminating the certificate in the path.

In this diagram, there are three containers running in an ECS cluster. The ECS cluster can be either the EC2 or Fargate launch type.

The following diagram shows an architecture that contains two different services deployed in two different ECS clusters.

In this architecture, the containers in each of the clusters can reference the other containers securely via the Network Load Balancer without terminating or offloading the certificates until it reaches the destination container.

This approach addresses the requirements where containers need to communicate securely whether they are deployed in one VPC, across VPCs, or in separate AWS accounts.

The following diagram below shows both TLS connections from the internet, as well as connections from within the same cluster.

The above approach is achieved by using the same Network Load Balancer for the cluster to serve two different services. Implement this by using two different target groups (one for each service) and associating them with the ECS task definition. The containers use the DNS name associated with the Network Load Balancer to access the containers in the other service.


The architectures in this post show how the Network Load Balancer integrates seamlessly with ECS and other AWS services, providing end-to-end TLS communication across services without offloading or terminating the certificates. This gives you the ability to use dynamic ports in ECS containers. It can also handle tens of millions of requests per second while maintaining high throughput at ultra-low latency for applications that require the TCP protocol.

If you have questions or suggestions, please comment below.