^{Internal reference: topics/04-1.md}

Here are a few use cases to run docker inside a docker container.

• One potential use case for docker in docker is for the CI/CD pipeline, where you need to build and push docker images to a container registry after a successful code build.
• Modern CI/CD systems support Docker-based agents or runners where you can run all the build steps inside a container and build container images inside a container agent.
• Building Docker images with a VM is pretty straightforward. However, when you plan to use Jenkins Docker-based dynamic agents for your CI/CD pipelines, docker in docker comes as a must-have functionality.
• Sandboxed environments.
• For experimental purposes on your local development workstation.

DinD creates a child container inside a Docker container. For this, you need either an official docker image with dind tag. The dind image is baked with the required utilities for Docker to run inside a docker container. Or you build it with a Dockerfile with more control for all added packages and configuration (see Exercises in this course)

(1) Create a container named i.e. dind-test with docker:dind image from Docker-Hub.

docker run --privileged -d --name dind-test docker:dind

(2) Log in to the container using exec.

docker exec -it dind-test /bin/sh

(3) When you list the docker images, you should see the Ubuntu image along with other docker images in your host.

docker images

(4) Now create a Dockerfile inside the test directory.

mkdir test && cd test

(5) Create a Dockerfile

nano Dockerfile

(6) Copy the following Dockerfile contents to test the image build from within the container.

FROM ubuntu:18.04
LABEL maintainer=Hans Muster <hmuster@example.com>
RUN apt-get update && \
    apt-get -qy full-upgrade && \
    apt-get install -qy curl && \
    curl -sSL https://get.docker.com/ | sh

(7) Build the Dockerfile

docker build -t test-image .

Daniel Garavaldi