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What is Clojure?

Clojure is a dialect of the Lisp programming language. It is a general-purpose programming language with an emphasis on functional programming. It runs on the Java Virtual Machine, Common Language Runtime, and JavaScript engines. Like other Lisps, Clojure treats code as data and has a macro system.

wikipedia.org/wiki/Clojure

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How to use this image

Build tools

Clojure has three major approaches to building and running projects:

  1. leiningen
    1. The oldest and probably most common tool
  2. boot
    1. An alternative approach that solves similar problems as leiningen
  3. tools-deps
    1. A more recent official tool for some of the lein/boot use cases

There are variants of this image for all three of these tools and their respective releases. The most basic form of these tags is:

  1. clojure:lein
  2. clojure:boot
  3. clojure:tools-deps

But you can also append a hyphen and the version of that tool you'd like to use. For example, for lein 2.8.1 you can use this image: clojure:lein-2.8.1.

Run your app with leiningen

Add a Dockerfile to an existing Leiningen/Clojure project with the following contents:

FROM %%IMAGE%%
COPY . /usr/src/app
WORKDIR /usr/src/app
CMD ["lein", "run"]

Then, run these 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 straightforward example of a Dockerfile, it does have some drawbacks. The lein run command will download your dependencies, compile the project, and then run it. That's a lot of work, all of which you may not want done every time you run the image. To get around this, you can download the dependencies and compile the project ahead of time. This will significantly reduce startup time when you run your image.

FROM %%IMAGE%%
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"]

Writing the Dockerfile this way will download the dependencies (and cache them, so they are only re-downloaded when the dependencies change) and then compile them into a standalone jar ahead of time rather than each time the image is run.

You can then build and run the image as above.

Compile your Lein/Clojure project into a jar from within the container

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 %%IMAGE%% lein uberjar

This will build your project into a jar file located in your project's target/uberjar directory.

More details

See the official image README for more details about using this image with boot and tools-deps.