A DevOps engineer is building a pipeline in AWS CodePipeline to build a docker image and push it to AWS ECR. In the CodePipeline, the source stage is configured with AWS CodeCommit where the source files are stored. In the build stage, the Action Provider is AWS CodeBuild. For its buildspec.yml file, there are three phases which are pre_build, build and post_build. The build stage in the pipeline is responsible for creating the image and pushing it to the ECR repository. Which command should be put in the pre_build stage in the buildspec.yml file?

Answer options:

A.docker build -t $REPOSITORY_URI:latest .
B.aws ecr get-login --region $AWS_DEFAULT_REGION
C.docker tag $REPOSITORY_URI:latest
D.docker push $REPOSITORY_URI:latest

Correct Answer – B
The buildspec.yml file includes a collection of build commands and related settings for AWS CodeBuild to run the build. Refer to
https://aws.amazon.com/blogs/devops/build-a-continuous-delivery-pipeline-for-your-container-images-with-amazon-ecr-as-source/
on how to use CodeBuild and CodePipeline to build an image for ECR.
Option A is incorrect: Because the docker build command should be put in the build phase.
Option B is CORRECT: The preparation steps should be put in the pre_build phase such as ecr login, getting the ECR repository URI and tags definition.
Option C is incorrect: Because the docker tag command happens after the docker image is built and should be put in the build phase.
Option D is incorrect: Because docker push should be put in the post_build phase as required after the image is built.