Load Balancing with Application Load Balancer (ALB) - AWS ECS Tutorial

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Load balancing is a critical component of building scalable and highly available applications in Amazon Elastic Container Service (ECS). The Application Load Balancer (ALB) is a powerful service provided by Amazon Web Services (AWS) that enables you to distribute incoming traffic to multiple ECS tasks or services. ALB intelligently balances the traffic based on various factors, such as the health of the tasks and the routing rules defined. This tutorial will guide you through the process of configuring load balancing with an ALB in ECS.

Load Balancing with Application Load Balancer (ALB)

To configure load balancing with an Application Load Balancer (ALB) in Amazon ECS, follow these steps:

  1. Create an ALB: Set up an ALB in the desired Amazon Virtual Private Cloud (VPC), configure the listener and target groups, and define the routing rules.
  2. Create a target group: Specify the ECS service as the target type and configure the target group to register the tasks in the ECS service.
  3. Configure health checks: Define health check settings for the target group to ensure that only healthy tasks receive traffic.
  4. Associate the target group with the ALB listener: Connect the target group to the ALB listener to enable traffic routing.
  5. Test the load balancing: Verify that the ALB is distributing traffic evenly across the ECS tasks and that the health checks are functioning as expected.

Example: Configuring an ALB

Here's an example of configuring an Application Load Balancer (ALB) using AWS CLI commands:

aws elbv2 create-load-balancer --name my-load-balancer --subnets subnet-12345678 --security-groups sg-12345678

aws elbv2 create-target-group --name my-target-group --protocol HTTP --port 80 --target-type ip --vpc-id vpc-12345678

aws elbv2 create-listener --load-balancer-arn arn:aws:elasticloadbalancing:us-west-2:123456789012:loadbalancer/app/my-load-balancer/1234567890123456 --protocol HTTP --port 80 --default-actions Type=forward,TargetGroupArn=arn:aws:elasticloadbalancing:us-west-2:123456789012:targetgroup/my-target-group/1234567890123456
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Common Mistakes

  • Not configuring health checks properly, leading to incorrect routing decisions and potential downtime.
  • Forgetting to update the ALB listener or target group configuration when making changes to the ECS service or task definitions.
  • Overlooking security group rules or NACL configurations that may block traffic to the ALB or ECS tasks.
  • Ignoring SSL/TLS termination settings or not properly configuring HTTPS listeners for secure traffic.
  • Not considering the scalability and performance requirements when selecting the ALB instance size.

Frequently Asked Questions

  1. Can I use multiple ALBs for my ECS tasks or services?

    Yes, you can configure multiple ALBs to distribute traffic to different ECS tasks or services based on specific routing rules.

  2. Can I use ALB with both EC2 and Fargate launch types in ECS?

    Yes, ALB is compatible with both EC2 and Fargate launch types in Amazon ECS.

  3. Can I configure SSL/TLS termination with ALB for secure traffic?

    Yes, ALB supports SSL/TLS termination, allowing you to offload SSL/TLS decryption and encryption at the load balancer.

  4. What is the difference between ALB and Classic Load Balancer (CLB) in ECS?

    ALB offers advanced features, such as content-based routing and support for HTTP/2, while CLB is a legacy load balancer that provides basic load balancing capabilities.

  5. Can ALB route traffic to ECS tasks in different availability zones?

    Yes, ALB can distribute traffic across ECS tasks running in different availability zones within a region.


Configuring load balancing with an Application Load Balancer (ALB) in Amazon Elastic Container Service (ECS) is crucial for ensuring scalability, high availability, and efficient traffic distribution. By following the step-by-step guide, avoiding common mistakes, and understanding the FAQs, you can successfully configure an ALB and leverage its powerful load balancing capabilities to enhance the performance and reliability of your containerized applications in ECS.