dockerized 0.13.0

Seamlessly execute commands in a container

dockerized 🏗❤️

dockerized is a tool for seamlessly executing commands in a container. It takes care of the details so you can run a command in a container as if it was running on your machine - just prepend any command with dockerized exec to have it run in the container.

This is especially useful for building things. For example, if your project needs Java and Maven to build, you can put these build dependencies in a Dockerfile and then just replace mvn with dockerized exec mvn. If your tests need a Postgresql database to run, add that in a Docker Compose file and just run dockerized exec mvn test.

That approach encourages versioning the build dependencies alongside the application code.

• Never again an outdated README file with all the tools you need to install to build your project.
• Never again your build dependencies managed in another repo which falls out of sync with your code.

Your build dependencies are part of your project!

Why not docker run or docker exec?

Fair question! After all dockerized is just a wrapper for Docker. You can definitely use docker run or docker exec but there are a few details you'd have to take care of:

Rebuilding the Docker image: after changing the Dockerfile, you need to run docker build before running docker run again. When iterating on the Dockerfile this can become a pain.

With dockerized you just do dockerized exec.

Volumes and working directory: to allow the developer to run commands from arbitrary locations within the project, you probably want to mount the project root into the container. Manually running docker run -v $PWD:... one time and docker run -v $PWD/..:... another time, or adding some script to do this for you.

With dockerized you just do dockerized exec.

Running Docker Compose: almost every project has integration tests. Running them locally usually means running Docker Compose. Now you need to run docker-compose up before running docker run. Besides being annoying, see also "Port contamination" below.

With dockerized you just do dockerized exec.

"Port contamination": many people run their tests on the host, against dependencies (think PostgreSQL for example) running in containers. Since the tests need to access the PostgreSQL port, they expose this port to the host. When you are working on multiple projects these exposed ports start conflicting and you have to docker-compose stop one project before docker-compose start the other.

With dockerized you just do dockerized exec.

Getting Started

Install dockerized:

pip install dockerized

Run dockerized init to set up. It will create a Dockerfile and a Docker Compose file for you. You can tweak those to set up your build dependencies.

Then run dockerized exec COMMAND to build the container, start the dependencies, and execute COMMAND inside a container.

Caching the 'dockerized' image

When running in CI dockerized probably runs on a fresh node where the 'dockerized' image is not available yet. Therefore, it needs to build it from scratch. This can be a long process of downloading and installing build dependencies. Doing this over and over again on every fresh node is wasteful.

Let's illustrate this using the following ./dockerized/Dockerfile.dockerized file:

FROM busybox
RUN echo "long operation"

Make the following changes to your ./dockerized/docker-compose.dockerized.yml file:

 version: '3.2'
 services:
   dockerized:
+    image: benzaita/dockerized-fixture-with_build_cache
     build:
       context: .
       dockerfile: Dockerfile.dockerized
+      cache_from:
+        - benzaita/dockerized-fixture-with_build_cache
     entrypoint:
       - sh
       - '-c'

dockerized first tries to pulls the dockerized image before building it so Docker can utilize it. If the image was built using the same Dockerfile, Docker will use the cache from benzaita/dockerized-fixture-with_build_cache instead of executing the RUN echo "long operation" line during build. When you run a command using dockerized exec you can expect the following:

Pulling dockerized ... done
Building dockerized
...
Step 2/2 : RUN echo "long operation"
 ---> Using cache
...

Pushing the cache image

Having a remote cache for the image means you need to decide when to update it -- when to run dockerized push.

It is recommended to run dockerized push at the end of your CI pipeline. This ensures that (a) the pipeline successfully runs with this dockerized image (so you don't push a broken image) and (b) incurs a very small overhead since in most of the builds the Docker image is already up to date and Docker does not push the layers.

Another option is to let the developer run dockerized push after they commit a change to the .dockerized/Dockerfile.dockerized file. This does not require any automation, but means the developer might forget to do it, rendering the cache out of date.