AWS CodeBuild Test Postgres Database Example

• Summary
• The Example
• DockerHub docker pull limits
• Is this a "Side Car" or "Docker in Docker"?
• References

Summary

In many projects, we need a database docker container for testing. We can easily run a container with an empty database, then destroy it automatically after testing. This repo gives you an example using AWS CodeBuild to run a "side-car" postgres container for testing.

The Example

In this example, we use the postgres:10.6-alpine image to run a postgres db in the background, and we use Python sqlalchemy to connect to the postgres db and run a simple SQL statement.

The buildspec.yml file is the AWS CodeBuild orchestration file.

• In install phase, we pulled the docker image from DockerHub
• In pre_build phase, we start a background postgres container
• In build phase, we installed the dependencies and run the test
• In post_build phase, we destroy the postgres container.

DockerHub docker pull limits

The DockerHub has 100 pull per IP per hour limits. You may easily hit this limits if you have many build runs. I recommend to use AWS ECR to cache the image you pulled from DockerHub. There's NO COST to transfer data from ECR to AWS CodeBuild if they are in AWS Region, see explanation here. AWS ECR will charge if you are pulling from non AWS Region, for example, your local laptop.

In buildspec file, you should add some logic to install phase:

1. if ECR doesn't have this image, we pull it, then re-tag it, and then push to ECR.
2. if the latest image in ECR was updated one month before, we pull it form DockerHub and push it again to ECR.
3. in pre_build phase, we always use image from ECR.

Is this a "Side Car" or "Docker in Docker"?

You can think of AWS CodeBuild is a VM in sandbox mode. The main build logic happens in container, however you can setup additional background container. In other words, this is NOT "Docker in Docker".

References

• postgres on DockerHub: https://hub.docker.com/_/postgres
• Background tasks in build environments: https://docs.aws.amazon.com/codebuild/latest/userguide/build-env-ref-background-tasks.html