How can I run an Amazon ECS task on Fargate in a private subnet?

Short description

You can run Fargate tasks in private subnets. However, based on your use case, you might require internet access for certain operations. For example, you might want to pull an image from a public repository. Or, you might want to prevent any internet access for your tasks.

To run Fargate tasks in a private subnet without internet access, use virtual private cloud (VPC) endpoints. VPC endpoints allow you to run Fargate tasks without the need to grant the tasks access to the internet. The required endpoints are accessed over a private IP address.

If you need your task to access the internet from a private subnet, then use a NAT gateway to grant internet access. The required endpoints are accessed over the public IP address of the NAT gateway.

Resolution

Create a VPC

Create an Amazon Virtual Private Cloud (Amazon VPC) with public or private subnets. Then, depending on your use case, follow the steps in Use a private subnet without internet access (VPC endpoints method). Or, follow the steps in Use a Private subnet with internet access.

Use a private subnet without internet access (VPC endpoints method)

To create interface endpoints and an Amazon Simple Storage Solution (Amazon S3) gateway endpoint, complete the following steps:

1. Create an Amazon S3 gateway endpoint.
2. Create Amazon Elastic Container Registry (Amazon ECR) interface endpoints.
3. For tasks that use AWS Secrets Manager to inject secrets into tasks and Amazon CloudWatch Logs, create interface endpoints for both services.
   Note: Security groups for these VPC endpoints allow inbound traffic on TCP port 443 from the Fargate task security group or Fargate task VPC CIDR range.
4. Follow the instructions in the Create an Amazon ECS cluster and service section of this article.

Use a private subnet with internet access

Create a NAT gateway. When you create your NAT gateway, complete the following tasks:

• Put your NAT gateway inside the public subnet.
• Update the route table of the private subnet:
  For Destination, enter 0.0.0.0/0.
  For Target, select the ID of your NAT gateway.

Then, follow the instructions in the Create an Amazon ECS cluster and service section of this article.

Create an Amazon ECS cluster and service

1. Create an Amazon ECS cluster. For Infrastructure, select AWS Fargate (serverless).
2. Create an Amazon ECS service.

When you configure the network for the Fargate service, complete the following tasks:

• Based on the method that you chose earlier, choose the private subnet that you configured for the VPC endpoints. Or, choose the subnet that you configured for the NAT gateway.
• For your security group, allow outbound traffic on port 443 to access Amazon ECS endpoints.