Sharing CircleCI configuration / Dockerfile to build, test, and push Elixir Docker images

cheerfulstoic · February 11, 2021, 9:53am

I spent quite a bit of time trying to find a good configuration to build / test my Elixir app in CircleCI and then push an image to Docker Hub. It is probably a somewhat common thing, but I did a lot of research and trial and error moving around different steps until I got it to a good point. I wanted to share in case in ended up being useful to somebody else searching Google

Features:

Uses Circle CI caching for dependencies / compiled files
Runs tests + code checks (using ex_check)
Builds and pushes images to Docker Hub:
- One tag with the Circle CI build number
- One tag with the git sha
- One tag with latest (if the current branch is main)
A Dockerfile is included which uses Docker’s multi-stage builds and Elixir releases so that the resulting images (for this simple app) ends up around 12.5 MB

I’ve made it available in a GitHub Gist:

gist.github.com

https://gist.github.com/cheerfulstoic/125bff73443d3ddd47963cb38f03269f

.circleci_config.yml

# file path should be .circleci/config.yml
version: 2  # use CircleCI 2.0 instead of CircleCI Classic
jobs:  # basic units of work in a run
  build:  # runs not using Workflows must have a `build` job as entry point
    parallelism: 1  # run only one instance of this job
    docker:  # run the steps with Docker
      - image: circleci/elixir:1.11.3  # ...with this image as the primary container; this is where all `steps` will run
        auth:
          username: $DOCKER_USER
          password: $DOCKER_PASS  # context / project UI env-var reference

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Dockerfile

# ---- Build Stage ----
FROM elixir:1.11.3-alpine AS builder

EXPOSE 80

ENV APP_HOME /app

RUN mkdir $APP_HOME
WORKDIR $APP_HOME

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Comments welcome here or there

dimitarvp · February 12, 2021, 10:47am

Thank you for sharing this! I’ll be trying it in the future.

Have you considered making other images not based on Alpine btw? I might try your Dockerfile with Ubuntu 20.04 which is one of the smaller images.

cheerfulstoic · February 12, 2021, 12:49pm

Yeah, absolutely try it with something else. I just used alpine because that’s what the example that I started from used

One note: at first I had alpine for the first stage but didn’t use it for the second stage and there were problems that I didn’t understand until I had done some searching around. So whatever you choose, I think you need to make sure both steps are using the same base linux distro