Rational

When building Docker image for a Clojure project, we endup testing outside of the final environment.

Here I try to benefit from Docker layers to build/test from the same Java environment that will be used to run the Docker image.

Continous Integration

Test

We can run the test step independently of the build of the complete image ⇒ we can run tests in a dedicated step of our CI pipeline

If we configure our test-runner to output results in a file (XUnit format), we can retrieve this file leveraging Docker volumes when calling "docker run"

➜ docker build --target test --tag clj-example-tests .
➜ docker run clj-example-tests:latest
# ... <SKIPPED>
[(.)]
1 tests, 1 assertions, 0 failures.

Let’s introduce a failing test

➜ cat >> test/exo/add_test.clj<< EOF
(deftest will-fail
  (is (= 1 (sum 1 1))))
EOF
➜ docker build --target test --tag clj-example-tests .

Here is output of the run

➜ docker run clj-example-tests:latest
# ... <SKIPPED>
[(F.)]
Randomized with --seed 875721236

FAIL in exo.add-test/will-fail (add_test.clj:11)
Expected:
  1
Actual:
  -1 +2
2 tests, 2 assertions, 1 failures.
➜ echo $?
1

At any time we can override the CMD to be executed in our test layer to execute different tests

For example:

➜ docker run clj-example-tests:latest clojure -M:test -m kaocha.runner --focus-meta :integration
# ... <SKIPPED>
[(.)]
1 tests, 1 assertions, 0 failures.

Build

Artifact is built in a "build" layer and later copied on a "deployment" layer that does not include all the build tools ⇒ lightweight docker image

➜ docker build --tag clj-example .
# ... <SKIPPED>
Successfully built 880afb3fef23
Successfully tagged clj-example:latest

Then we can execute our program

➜ docker run clj-example:latest 1 2 3
Result: 6

Here are image sizes involved in this pipeline

➜ docker image list
REPOSITORY    TAG       IMAGE ID       CREATED          SIZE
clj-example   latest    533dd371f7ba   7 seconds ago    342MB
<none>        <none>    afed52b6047a   8 seconds ago    468MB
<none>        <none>    ab0222b7d14a   13 seconds ago   463MB
ubuntu        focal     2b4cba85892a   43 hours ago     72.8MB

DevContainer

DevContainer configuration is provided in .devcontainer/devcontainer.json

It is reusing test layer ⇒ Clojure and our dependencies are already installed ⇒ jack-in is really fast

That is allowing us to develop in the exact same environment that will be used to validate in the CI or deploy our application