Using Docker and CircleCI with Hakyll

Juan Pedro Villa published a great article (Dr. Hakyll: Create a GitHub page with Hakyll and CircleCI) explaining how to use circleci to provide continuous deliver for a hakyll site.

However, I ran into some trouble with circleci. My builds kept timing out or I’d get a cabal build error. So I figured I should take advantage of circleci’s docker support.

I started off with a simple docker image that has every thing I need to build the site.

FROM rdesfo/stack:latest
Maintainer Ryan Desfosses <ryan@desfo.org>

RUN stack setup --compiler ghc-7.10.3

RUN stack install --resolver lts-6.25 hakyll

Now that I have the docker image I can use the same git repo that I setup following Juan outlined in his article. The only difference I ran into was that I had to add a -f to the submodule command since I had added _site to my .gitignore file.

git submodule add -f https://github.com/rdesfo/hakyll-test.git _site

The next step was to tell circleci to use docker to carry out the build steps. I started out with the following, but came to find out that circleci doesn’t currently support docker exec.

machine:
  services:
    - docker

dependencies:
  override:
    - docker pull rdesfo/hakyll

test:
  override:
    - docker run -d --name hakyll -i rdesfo/hakyll bash
    - docker cp . hakyll:/home/user/app/
    - docker exec -u root hakyll chown -R user:user /home/user/app
    - docker exec -u user hakyll sh -c "cd /home/user/app; stack build; stack exec -- site build"

Fortunately, circleci has some great documentation that provides a work around. It’s not pretty, but I was able to replace docker exec with the following lxc-attach.

 - sudo lxc-attach -n "$(docker inspect --format "{{.Id}}" hakyll)" -- bash -c "chown -R user:user /home/user/app"
    - sudo lxc-attach -n "$(docker inspect --format "{{.Id}}" hakyll)" -- su user - bash -c "export LANG='C.UTF-8'; cd /home/user/app; stack build; stack exec -- site build"

The full circleci yaml file can be found here.