Deploying Native Reason/OCaml with Zeit's


I'm working on a new ReasonReact project that will need a stateful server, and I thought it might be nice to write that in Reason too :) but what's the best way to deploy it? And by "best" I mean "easiest, with a free-to-try option". After looking around a little, I settled on Zeit's

What did I end up with? A 10mb docker image with a server inside!

For the server code, I'm just taking cohttp's example server. The full source for this example is here.

Making the Docker image

## This is a two-stage docker file
# This first stage has opam & a ton of other things
# inside it. The full image is 1.4Gigs! Which is way
# too big to keep around.
FROM ocaml/opam:alpine as base

RUN sudo apk update
RUN sudo apk add m4
RUN sh -c "cd ~/opam-repository && git pull -q"
RUN opam update
# We'll need these two whatever we're building
RUN opam install dune reason > /dev/null 2>&1

# need these two for building tls, which is needed by cohttp
RUN opam depext conf-gmp.1
RUN opam depext conf-perl.1
RUN opam install tls > /dev/null 2>&1
# these are the dependencies for our server
RUN opam install lwt cohttp cohttp-lwt-unix > /dev/null 2>&1

# Now we copy in the source code which is in the current
# directory, and build it with dune
COPY --chown=opam:nogroup . /hello-reason
WORKDIR /hello-reason
RUN sh -c 'eval `opam config env` dune build bin/Server.exe'

## Here's the second, *much* leaner, stage
# It only contains the server binary! The reason we can do this
# is we statically linked the binary (with -ccopt -static)
FROM scratch
COPY --from=base /hello-reason/_build/default/bin/Server.exe /server
CMD ["/server"]

docker build -t hello . will take a minute, but at the end we get our 10mb image!

hello         latest   15ebe8ca2a7d   8 hours ago   9.85MB

Now run the docker image locally to make sure it's working

docker run -d -p 4321:8000 hello

If you open up http://localhost:4321, You should see something like this:

Hello folks! This site has been visited 1 times

Uri: //
Method: GET
Headers: accept: text/html
accept-encoding: gzip, deflate
connection: keep-alive
upgrade-insecure-requests: 1


Deploying with Now

This part is so easy it's almost not even worth mentioning. Once you've installed now, you go to the directory with the Dockerfile and run now and it all just works! The first time you run it, the deploy will take a while because it's building the docker image for the first time. Subsequent builds will use the image cache, however, and will be much faster.

That's all, folks!

With OCaml native deployment this easy, there's no excuse not to do it! Now all we need are some super-easy-to-use server libraries... 🤔 cohttp and httpaf are quite powerful, but are a far cry from express.js or rust's rocket.