Verify Docker Images Build By Docker-In-Docker

I choose to use Docker-In-Docker to verify image build. Why? Yes, I know many people are strongly against dind(docker-in-docker). Like this one.[1]

With my years’ experience, I’m confident that dind is very capable for this scenario:

1. Super easy to setup and run. Literally we only need to use “docker run”, then perform tests.
2. Leave no trace or garbage in docker host. If using a shared host, people’s daily work might be disturbed by our tests.

For your convenience, I’ve published a docker image(See Dockerfile).GitHub

# Pull docker image
docker pull denny/docker:v1.0

# Start a container to build images inside
docker run -t -d --privileged -h dockerimages \
  --name docker-images denny/docker:v1.0 /usr/bin/dockerd

# Login to the container
docker exec -it docker-images bash

# Download a dockerfile for test purpose
wget -O /root/java_v1_0.dockerfile \
  https://raw.githubusercontent.com/dennyzhang/devops_docker_image/tag_v6/java/java_v1_0.dockerfile

# Build docker image inside current container
cd /root/
docker build -f java_v1_0.dockerfile -t denny/java:v1.0 --rm=true .

# Verify docker images
docker images | grep denny/java

1. Don’t use devicemapper as your storage driver. By default, containers can only have 10GB disk. Yes, we could mount volume for big folders. Still, inconvenient.
2. Stop containers first, before decommission. At the end of testing, make sure we stop containers first, then stop dockerd and finally destroy the env.
3. When building multiple images, the sequence matters. Let’s say, image B might depends on image A. If image A is public, do we still need to care about the test sequence? The answer is yes. We need to build B based on latest A, instead of the version in docker hub.
4. Speed up image build by loading frequently used golden images first. The pre-loading would not only save us lots of time, but also the false negatives of network turbulence.

# Export docker image
docker save ubuntu:14.04 > ubuntu_1404.tar.gz
# Import docker image
docker load -i ubuntu_1404.tar.gz

Here comes Jenkins job (BuildAllDockerImages). You can also find a live demo here.
GitHub

[1] https://jpetazzo.github.io/2015/09/03/do-not-use-docker-in-docker-for-ci/

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Blog URL: https://www.dennyzhang.com/verify_image_build