DevSpace(s)-ify your existing container images

This is a proposed approach for how to take any existing UBI-based language image, and turn it into a Dev Spaces optimized container image. Dev Spaces/Eclipse Che have introduced us to this concept that a container platform can be used, not just to host production applications, but also as a place optimized for developers to write, test and commit code. By running a development workspace with an IDE inside of a container and serving it through the browser, we can extend all of the consistency, immutability, and portability benefits of our application runtime environments to inner-loop development.

However, there is one challenge we have to deal with when working in this mode -- our production container images have been optimized for production. That means that they only contain the minimal tooling & libraries required to run our application and nothing for the developer. In a developer workspace, we need to have a few more tools available to us to make our development experience as smooth and efficient as possible. Thus far we've solved this problem by managing completely separate images for the purpose of development and deployment. However this creates additional overhead in having to manage the build process for these two sets of images.

A better experience could be just taking our existing application runtime images, and layering on top a standard set of developer tools to produce developer-optimized versions of our production images.

Developer-optimized container images using CEkit

CEkit is a modular, YAML-based framework for generating Containerfile-driven images that can be built using Docker, Podman or Buildah. To acheive our developer-optimized image builds, we're going to use a 3 layered approach:

1. A base image that already contains the language, framework, or libraries we need to run our app. In this case we're selecting language images built on top of Red Hat's Universal Base Images
2. A developer base layer that provides all the basic tools and libraries generally desired for running workspaces. Based on the Devfile.io Developer Base Image.
3. A custom tooling layer that contains organization or team specific tools, such as CLIs for interacting with your container platform, public cloud or other hosting environment. For the purpose of this demo, we're just adding zsh and the Oh My ZSH! project.

With CEkit, each layer that we add can be represented by a module that defines packages and setup steps for that layer.

Building Images

To get started download and install CEkit.

To start off, let's just build our generic developer base image. This image will simply contain our developer base and custom tooling layers on top of a base

Developer Base Image:

cekit build podman

The developer base image is defined in the image.yaml file which is automatically picked up by CEkit. The image.yaml defines the name, version (tag), base image and modules that will be used to compose the image.

Using Overrides to inject language images

CEKit also supports overrides. Overrides allow you to modify certain parts of a build to produce slightly different variations of an image without defining a completely separate build. For our purposes, we're going to use overrides to inject an alternate language image as our FROM image.

To build a Java OpenJDK 17 version of our image, we can run:

cekit build --overrides developer-openjdk-17.yaml podman

To build a NodeJS 18 image, run:

cekit build --overrides developer-nodejs-18.yaml podman

Need a Containerfile? You Got it!

If you still have a need or desire to provide a raw Containerfile for people to build, CEkit has you covered there too. In addition to the build image, the cekit build command also outputs the full source for the image, including a generated containerfile, which can be built directly usin Docker, Podman or Buildah. For example, after running the NodeJS example above, I can also run:

podman build -t nodejs-containerfile target/image

This is useful for supporting a mixed mode where you want to have a streamlined CI process for producing images for your project, but would also like to make it easy for consumers of your project to build the images themselves without extra tooling.

Quick Commands to build images

cekit build --overrides images/cekit-builder.yaml podman --tag quay.io/etsauer/cekit-builder:dev