One of the last things left to figure out when I was about to lauch this website was finding a workflow to nicely deploy it. I was using Jekyll + Github Pages for my old website and it was working well enough for me so I didn’t want to radically change the way I was doing things. On the other hand I didn’t update my old website in a while and I am new to Hakyll so I had to figure out if I could keep a similar workflow. I ended up spending a few hours figuring out a solution I was happy with and the following is a description of my present workflow and how I got to it. On the Hakyll website there are a few blog posts on the topic. I initially blindly followed the one using CircleCI but I wished there was a simpler solution not involving git submodules; on the other hand the other was simple but focused developing on a local machine. I wished I could find a solution that combined both and I ended up finding it thanks to the fact that CircleCI rolled out their 2.0 release.

Setting up CircleCI 2.0

Configuration files in CircleCI 2.0 are quite different from 1.0 so I couldn’t reuse much of the code in this post but I found the docs quite good and the whole configuration options quite intuitive. CircleCI 2.0 adds great support for Docker, so I ended up creating a custom docker image for my website after trying the official Haskell image and stumbling upon two main issues:

  1. ssh isn’t installed by default: this is a problem when checking out or pushing to a remote git repository (checkout actually works somehow thanks to some tricks CircleCI does but it logs a warning in its console)
  2. make isn’t installed by default: my website uses hakyll-sass that has a C++ dependency - libsass - that needs to be built

After that the project was building but it was compiling all dependecies. Building a site from scratch takes quite a bit - ~20 minutes on my local machine and ~12 minutes in CircleCI - so it’s critical to use CircleCI’s caching to speed things up. The save_cache and restore_cache job-level keys are the ones to configure in order to speed up the build, this is how the caching section looks for my project:

  - restore_cache:
      key: v1-stack-{{ checksum "futtetennismo.cabal" }}
  - save_cache:
        - ~/futtetennismo/.stack-work
        - /root/.stack/
      key: v1-stack-work-{{ checksum "futtetennismo.cabal" }}

It’s very simple: just let CircleCI know that it should cache and how the cache should be named in order to be retrieved at a later time. The improvements on build time are dramatic: from ~20 minutes in case of build with no cache to ~2 minutes in the worst case (when a new cache archive needs to be created and uploaded) to ~30 seconds in the average case!


Here’s something to keep in mind when caching in CircleCI 2.0

The cache for a specific key is immutable and cannot be changed once written.

In early experiments the save_cache job-level key in my config.yml looked like this

  - save_cache:
        - ~/futtetennismo/.stack-work
      key: stack-work-{{ checksum "futtetennismo.cabal" }}

but every new build was again taking a long time because the cache was mostly useless. Then I added root/.stack to the paths but still nothing, the cache was just a few under KB. At that point I noticed this tip in the docs:

Tip: Given the immutability of caches, it might be helpful to start all your cache keys with a version prefix v1-… . That way you will be able to regenerate all your caches just by incrementing the version in this prefix.

That meant that save_cache never overwrites an existing cache! I ended up building a new cache following that tip.

SSH keys

The missing piece in the puzzle is now setting up ssh key in CircleCI to be able to checkout the project and push new versions of the website. I ended up creating a read/write deployment key for pushing to github and a checkout key for fetching from github. The latter is just a matter of a few clicks, the former involves some manual work but the docs by the Github folks are easy to follow.

UPDATE: if a read/write deployment key is created and added to a project in CircleCI, there’s actually no need to also have a checkout key.

Bonus goodness

One feature that CircleCI provides (and which proved to be extremely handy when debugging some issues setting up ssh keys) is the ability to connect to a running container via ssh. Bravo to the CircleCI folks!


The workflow I ended up adopting is a mix of this two tutorials. The master branch - which is the one deployed by Github Pages in case of a user page - contains all the static assets of the website like images, html, css etc. Another branch - that I arbitrarily named source - contains all source code and each time a new commit is pushed to that branch CircleCI will build a version of my website and will eventually push it to Github (if the build succeeds). For convenience, I also configured my build in such a way that CircleCI builds only that branch. Here’s a snippet of the deploy job-level key in the config.yml:

version: 2
    working_directory: ~/futtetennismo
      - source
  - deploy:
      name: Deploy master to Github Pages
      command: |
        git config --global [email protected]
        git config --global CircleCI
        stack exec site rebuild
        git checkout master
        git pull --rebase
        # Overwrite existing files with new files
        cp -a _site/. .
        #  Commit
        git add --all
        git commit -m "[`date '+%F %T %Z'`] New release"
        # Push
        git push origin master:master

As a last little bonus, I wrote a simple pre-push hook to open my browser and follow the deployment:

#!/usr/bin/env sh

if [ $(git rev-parse --abbrev-ref HEAD) == 'source' ]
    open ""

Wrapping up

I described a workflow to be able to deploy websites built with Hakyll in a fully automated fashion using Github Pages and CircleCI 2.0 and I pointed out some of the gotchas I learned in the process. The code is open source and can be found on Github.