Reusing CodeBuild by Passing and Overriding Environment Variables from CodePipeline

A story about reusing CodeBuild instead of needlessly creating new ones.

Managing buildspec with Terraform

• buildspec.yml

---
version: 0.2

env:
  variables:
    FOO: "${foo}"
    ...

• codebuild.tf

data "template_file" "buildspec" {
  template = file("buildspec.yml")

  vars = {
    foo = "foo"
  }
}

resource "aws_codebuild_project" "foo" {
  source {
    type      = "CODEPIPELINE"
    buildspec = data.template_file.buildspec.rendered
  }

When you run terraform apply to create the CodeBuild project, the environment variable FOO=foo is set.

Overriding CodeBuild Environment Variables from CodePipeline

This is useful when the CodeBuild processing is the same but you only want to change the environment variables.

resource "aws_codepipeline" "moge" {
  stage {
    name = "Build"

    action {
      configuration = {
        ProjectName = aws_codebuild_project.foo.name
        EnvironmentVariables = "[{\"name\":\"FOO\",\"value\":\"moge\",\"type\":\"PLAINTEXT\"}]"
      }

Now when you run CodePipeline, FOO=moge is specified and the value is successfully overridden.

Example

By substituting the nginx ECR repository into ${repository_url}, you can create a CodeBuild project that builds the Nginx image and pushes it to ECR.

---
version: 0.2

env:
  variables:
    DOCKER_BUILDKIT: 1
    REPOSITORY_URL: "${repository_url}"

phases:
  pre_build:
    commands:
      - $(aws ecr get-login --region $AWS_DEFAULT_REGION --no-include-email)
      - IMAGE_TAG=$(echo $CODEBUILD_RESOLVED_SOURCE_VERSION | cut -c 1-7)
  build:
    commands:
      - >-
        docker build -t $REPOSITORY_URL:latest -f Dockerfile .
      - docker tag $REPOSITORY_URL:latest $REPOSITORY_URL:$IMAGE_TAG
      - docker push $REPOSITORY_URL:latest
      - docker push $REPOSITORY_URL:$IMAGE_TAG

By specifying the environment variable REPOSITORY_URL=123456789012.dkr.ecr.ap-northeast-1.amazonaws.com/fluentd in CodePipeline, you can build the fluentd image and push it to ECR.

Conclusion

Don’t create CodeBuild projects recklessly.

That’s all.
I hope you find this helpful.

References

I referred to the following for how to specify environment variables.

Build specification reference for CodeBuild