ecs-error-no-container-instances-found

When attempting to launch a Docker container using AWS ECS, a common stumbling block is encountering the error: “No Container Instances were found in your cluster.” This happens when ECS tries to find available EC2 instances to deploy your containers but none are properly configured or available in your cluster. Here’s how you can resolve this error and successfully run your ECS tasks.

Understanding ECS and EC2 Interaction

AWS ECS (Elastic Container Service) can use either EC2 instances or AWS Fargate to launch containerized applications. When using the EC2 launch type, ECS requires EC2 instances to act as hosts for your Docker containers. These instances must be part of the ECS cluster before tasks can be executed.

AWS Fargate Option: If you prefer a serverless option where managing the EC2 instances isn’t necessary, consider using AWS Fargate. Fargate automatically handles instance provisioning, but it’s crucial to ensure your tasks are defined to use the Fargate launch type and appropriate networking configurations.

Steps to Create ECS-Optimized EC2 Instances

To resolve the “No Container Instances were found in your cluster” error, you need to provision ECS-optimized EC2 instances within your cluster. Here’s a step-by-step guide:

1. Launch an EC2 Instance:

   • Log in to the AWS Management Console.
   • Navigate to the EC2 Dashboard.
   • Click “Launch Instance.”

2. Select an ECS-Optimized AMI:

   • In the “Choose an Amazon Machine Image (AMI)” section, go to “Community AMIs.”
   • Search for “ecs-optimized.” Choose an AMI that fits your technical and performance needs.

3. Configure Instance Details:

   • Click “Next: Configure Instance Details.”
   • Under “IAM role,” select or create an IAM role named ecsInstanceRole.
   • Attach the AmazonEC2ContainerServiceforEC2Role policy to this role. This policy grants necessary permissions for the instance to connect with ECS and retrieve container tasks.

4. Networking and Security:

   • Ensure your VPC and subnets are correctly set up for your ECS cluster.
   • Create a security group allowing inbound traffic on the ports your application needs—commonly port 80 for web applications.

5. Review and Launch:

   • Continue with configuring storage and tagging your instance.
   • Review and launch the instance.

6. Integrate with ECS:

   • Once your instance is running, check the ECS console to ensure it appears under the “ECS Instances” section in your cluster. You might need to give it a few minutes for the registration process.

By following these steps, you’ll enable ECS to successfully find and utilize the EC2 instances for container deployment.

Resource Reference: For more detailed step-by-step guidance, refer to the official AWS documentation on Launching an Amazon ECS-optimized AMI.