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Last pushed: 25 days ago
Short Description
Clojure is a dialect of Lisp that runs on the JVM.
Full Description

Supported tags and respective Dockerfile links

Quick reference

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

How to use this image

Start a Lein/Clojure instance in your app

Since the most common way to use Clojure is in conjunction with Leiningen (lein), this image assumes that's how you'll be working. The most straightforward way to use this image is to add a Dockerfile to an existing Leiningen/Clojure project:

FROM clojure
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 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"]

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 clojure lein uberjar

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

Image Variants

The clojure images come in many flavors, each designed for a specific use case.

clojure:<version>

This is the defacto image. If you are unsure about what your needs are, you probably want to use this one. It is designed to be used both as a throw away container (mount your source code and start the container to start your app), as well as the base to build other images off of.

clojure:onbuild

The ONBUILD image variants are deprecated, and their usage is discouraged. For more details, see docker-library/official-images#2076.

While the onbuild variant is really useful for "getting off the ground running" (zero to Dockerized in a short period of time), it's not recommended for long-term usage within a project due to the lack of control over when the ONBUILD triggers fire (see also docker/docker#5714, docker/docker#8240, docker/docker#11917).

Once you've got a handle on how your project functions within Docker, you'll probably want to adjust your Dockerfile to inherit from a non-onbuild variant and copy the commands from the onbuild variant Dockerfile (moving the ONBUILD lines to the end and removing the ONBUILD keywords) into your own file so that you have tighter control over them and more transparency for yourself and others looking at your Dockerfile as to what it does. This also makes it easier to add additional requirements as time goes on (such as installing more packages before performing the previously-ONBUILD steps).

clojure:alpine

This image is based on the popular Alpine Linux project, available in the alpine official image. Alpine Linux is much smaller than most distribution base images (~5MB), and thus leads to much slimmer images in general.

This variant is highly recommended when final image size being as small as possible is desired. The main caveat to note is that it does use musl libc instead of glibc and friends, so certain software might run into issues depending on the depth of their libc requirements. However, most software doesn't have an issue with this, so this variant is usually a very safe choice. See this Hacker News comment thread for more discussion of the issues that might arise and some pro/con comparisons of using Alpine-based images.

To minimize image size, it's uncommon for additional related tools (such as git or bash) to be included in Alpine-based images. Using this image as a base, add the things you need in your own Dockerfile (see the alpine image description for examples of how to install packages if you are unfamiliar).

License

View license information for the software contained in this image.

Docker Pull Command

Comments (3)
nareka
a year ago

Anyone else seeing this?
$ docker run -it --rm -v "$PWD":/usr/src/app -w /usr/src/app clojure lein uberjar Couldn't find project.clj, which is needed for uberjar

whamtet
2 years ago

For even better performance add

:local-repo "repo"

to project.clj and type lein deps before building the docker container. The dependencies will all be copied into the container.

theremix
2 years ago

VIRTUAL SIZE 671.2 MB