What is Clojure?
Clojure is a dialect of the Lisp programming language created by Rich Hickey. Clojure is a general-purpose programming language with an emphasis on functional programming. It runs on the Java Virtual Machine, Common Langauge Runtime, and JavaScript engines. Like other Lisps, Clojure treats code as data and has a macro system.
As the most common way to use Clojure is in conjunction with lein, the Clojure image assumes you are doing so. The most straight-forward way of using this image is adding a Dockerfile to an already existing Lein/Clojure project.
FROM clojure
COPY . /usr/src/app
WORKDIR /usr/src/app
CMD ["lein", "run"]
Then run the commands to build and run the image.
docker build -t my-clojure-app .
docker run -it --rm --name my-running-app my-clojure-app
While the above is the most straight-forward example of a Dockerfile, it has several drawbacks. The lein run command will download your dependencies, compile the project, and then run it. That's a lot of work being done, and it may not be that you want that done every single time you run the image. We can download the dependencies ahead of time, as well as compile the project, so that when you run your image, the startup time is significantly reduced.
FROM clojure
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app
COPY project.clj /usr/src/app/
RUN lein deps
COPY . /usr/src/app
RUN mv "$(lein uberjar | sed -n 's/^Created \(.*standalone\.jar\)/\1/p')" app-standalone.jar
CMD ["java", "-jar", "app-standalone.jar"]
This Dockerfile will cause the dependencies to be downloaded (and cached so that they are only redownloaded when the dependencies change, rather than everytime the image is built) and compiled into a standalone jar when it is built rather than each time it is run.
Then build and run the image.
docker build -t my-clojure-app .
docker run -it --rm --name my-running-app my-clojure-app
If you have an existing Lein/Clojure project, it's fairly straightforward to compile your project into a jar from a container.
docker run -it --rm -v "$(pwd)":/usr/src/app -w /usr/src/app clojure lein uberjar
This will build your project into a jar file located in your project's target/uberjar directory for you to use.
If you have any questions about the image, please contact us through a GitHub issue or in the IRC channel #docker-library on Freenode.
If you want to contribute new features or updates, we are always thrilled to receive pull requests, and do our best to process them as fast as possible.
We recommend discussing your plans through a GitHub issue before starting to code - especially for more ambitious contributions. This gives other contributors a chance to point you in the right direction, give feedback on your design, and maybe point out if someone else is working on the same thing.