Pull Request Previews with Github Actions, AWS App Mesh, and ECS

Let's say you have an ECS based service: www.example.com, and when someone opens a pull request, you'd like to be able to preview what that branch looks like when deployed.

Our approach is to create a Github Actions workflow that

• builds and deploys an ECS Service as Virtual Nodes
• creates an App Mesh Virtual Service that points to the Virtual Nodes
• creates an App Mesh Virtual Gateway Route that routes <pr-number>.pr-preview.example.com to that Virtual Service.

Application Infrastructure

The supporting application infrastructure is deployed using terraform as it is mostly stable.

Broadly speaking, the following is created:

• An Elastic Load Balancer
• An ECS cluster
• A DNS entry for *.pr-preview.example.com pointing to the Elastic Load Balancer.
• An AppMesh Virtual Gateway configuration registered to the ELB
• An AppMesh Virtual Gateway ECS deployment
• IAM and other resources for use by the application.

See the example implementation for details.

Notes

• We choose EC2 flavor ECS cluster so that we can take advantage of local file system caching, but you don't have to.
• This example doesn't include autoscaling configuration.

Github Actions

The preview stack is dynamically deployed using Github Actions when a pull request is opened.

After the pull request is merged (or closed), the preview stack is deleted.

The preview stack is composed of:

• ECS Service:
  • Task Definition
  • Service Definition
• AppMesh configuration:
  • Virtual Node
  • Route
  • Virtual Router
  • Virtual Service
  • Virtual Gateway Route