Deploying Snap with Docker


Previous Post – Working With Snap 1.0

In our previous post we built out a scaffold project with Snap 1.0. In this post we’ll go over building a simple Dockerfile to deploy the project.

Make sure you’ve installed docker

Building the Haskell Base

There is an effort to make a docker official haskell image so we’ll use that. Once it’s merged into docker-library, we can simply skip building the docker-haskell from scratch.

Clone docker-haskell and switch to the docker-library branch. (It doesn’t matter where on the computer we do this)

git clone
cd docker-haskell
git checkout docker-library

Once in the appropriate directory, we can build the image with dockerbuild. -t is short for --tag, which lets us tag an image. We’ll use haskell for the base name and tag it as 7.8. Finally, the . tells docker where to find the dockerfile we’re building.

cd 7.8
docker build -t haskell:7.8 .

We can test that it worked by using dockerrun to spawn ghci as an interactive pseudo-tty.

docker run -i -t haskell:7.8 ghci

Use :q to quit ghci as usual.

Building our Project

We’ll base our project on the docker image we just built.

NOTE: We can push this base image to the docker hub but interestingly enough, we don’t have to (if we’re using “normal” repos; Automated Builds are a different story). We can push the final image without pushing the base image.


Our Dockerfile goes in the root of the auth-server/ folder. If you’ve built a haskell project before and are familiar with cabal sandboxes, this will be similar:

FROM haskell:7.8
RUN cabal update
# Add Cabal File and deps/ folder
ADD ./auth-server.cabal /opt/auth-server/auth-server.cabal
ADD ./deps /opt/auth-server/deps
# Create Sandbox and Add Source Deps
RUN cd /opt/auth-server &&
cabal sandbox init &&
cabal sandbox add-source deps/io-streams-haproxy &&
cabal sandbox add-source deps/snap &&
cabal sandbox add-source deps/snap-core &&
cabal sandbox add-source deps/snap-server &&
cabal sandbox add-source deps/snap-loader-static &&
cabal sandbox add-source deps/heist
RUN cd /opt/auth-server && cabal install --only-dependencies
# Explicitly add relevant folders
ADD ./src /opt/auth-server/src
ADD ./snaplets /opt/auth-server/snaplets
ADD ./static /opt/auth-server/static
# Init logging directories
RUN mkdir /opt/auth-server/log
# Build the Project
RUN cd /opt/auth-server && cabal build
# The directory CMD works from
WORKDIR /opt/auth-server
CMD ["./dist/build/auth-server/auth-server"]

With the above dockerfile in the root of auth-server/ we can build with:

cd auth-server
docker build -t auth-server .

NOTE: -t auth-server could be any name, such as -t myawesomething but if you plan to push it to the docker hub do username/image-name:tag-name

After building, run it with:

docker run -i -t -p 8000:8000 auth-server

and we should have a running instance of our application on port 8000 (or at boot2docker ip on port 8000).

To The Hub!

We can push the image we just built to a registry (such as the docker hub) by building it with our username (so it gets filed under our user on the hub):

docker build -t biscarch/auth-server
docker push biscarch/auth-server

and on some other computer (such as AWS, a Digital Ocean instance or another dev computer) pull and run the image:

docker pull biscarch/auth-server
docker run -d -p 8000:8000 biscarch/auth-server

after running, we can check that it’s up with docker ps:

Screenshot 2014-10-14 20.26.19


The completed docker image is on the hub as biscarch/auth-server:, so you can run a pull, then a run anywhere you like:

docker pull biscarch/auth-server:
docker run -i -t -p 8000:8000 biscarch/auth-server:

Join the Newsletter

My newsletter is where you'll find exclusive content from me. I write about technology, startups, and why you shouldn't call yourself a junior engineer

Web Mentions