7

Leiningen: Split an uberjar into dependencies.jar and app.jar (to optimize Docke...

 2 years ago
source link: https://blog.jakubholy.net/leiningen-split-uberjar-into-dependencies-and-app/
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.

Leiningen: Split an uberjar into dependencies.jar and app.jar (to optimize Docker layers and AWS Lambda functions)

November 19, 2019

I want to split my application uberjar into a separate JAR with only the dependencies and a JAR with only the application code so that I can upload them as separate “layers” and thus leverage layer caching. While my code changes frequently and is tiny, the dependencies change rarely and are much bigger. If I can add them as a separate Docker layer or AWS Lambda layer then this can be cached on the server and reused when I upload a new version - saving time, bandwidth, and money.

I was able to figure how how to do that with Leiningen thanks to the invaluable help of mikerod at the #leiningen channel:

project.clj

(defproject myapp "0.1.0-SNAPSHOT"
  :dependencies [...]
  :target-path "target/%s/"                                     ;; (1)
  :auto-clean false                                             ;; (2)
  :profiles {:jar     {:jar-name "myapp.jar"                    ;; (3)
                       :main minbedrift-uav.core ; actually not needed
                       :aot [minbedrift-uav.core]}
             :uberjar {:uberjar-name "myapp-dependencies.jar"   ;; (4)
                       :uberjar-exclusions [#"README.md" "project.clj"]
                       :source-paths ^:replace []
                       :resource-paths ^:replace []}}
  :aliases {"jar" ["with-profile" "jar" "jar"]})                ;; (5)

Highlights

  1. Store jar and uberjar build artefacts separately so that they do not mess up with each other

  2. Disable :auto-clean so that building the uberjar won’t delete the jar

  3. Move the :main and :aot from the top level into the new :jar profile so that they are not run during uberjar-ing (it seems that :main cannot be overriden to nil in :uberjar; and with nil we cannot apply ^:replace)

  4. Configure the uberjar to have empty (re)source paths and thus not include the application code; here ^:replace is crucial

  5. Add a convenience alias so that lein jar will automatically activate the jar profile

Dockerfile

FROM azul/zulu-openjdk-alpine:11-jre

WORKDIR /app
COPY /target/uberjar/myapp-dependencies.jar /app/
COPY /target/jar/myapp.jar /app/

CMD java -Dfile.encoding=UTF-8 -cp myapp-dependencies.jar:myapp.jar myapp.core

The crucial thing here is to include the dependencies before the application code.

Building

lein do clean, jar, uberjar
docker build -t myapp .

(Notice that we have to clean manually now.)

Alternatives

Alternatively we could use e.g. the lein-libdir plugin to copy all dependencies into a directory and include their jars individually (e.g. COPY /lib/*.jar /app/)

Are you benefitting from my writing? Consider buying me a coffee or supporting my work via GitHub Sponsors. Thank you! You can also book me for a mentoring / pair-programming session via Codementor or (cheaper) email.

Allow me to write to you!

Let's get in touch! I will occasionally send you a short email with a few links to interesting stuff I found and with summaries of my new blog posts. Max 1-2 emails per month. I read and answer to all replies.


report

Recommend

About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK