Docker Buildx and Platform-specific Images
Published on 14 March 2022.
Problem
I am playing around with a new build pipeline. I want to be able to create Spring Boot applications and build Docker images that can run on a Raspberry Pi computer. Because the Pi uses an ARM processor the image build step is more involved. In this post, I will outline how I built an ARM-specific image from my Spring Boot demo codebase.
Required
- Java 8
- Maven (mvnw packaged with repo)
- Docker
Build Steps
Maven
First, we use Maven to compile the Java code into a JAR. This can be accomplished from the commandline.
mvnw spring-boot:build-image
Successful build console output:
[INFO] Scanning for projects...
[INFO]
[INFO] --------------------------< dev.michael:demo >--------------------------
[INFO] Building demo 0.0.1
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] >>> spring-boot-maven-plugin:2.6.3:build-image (default-cli) > package @ demo >>>
[INFO]
[INFO] --- maven-resources-plugin:3.2.0:resources (default-resources) @ demo ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Using 'UTF-8' encoding to copy filtered properties files.
[INFO] Copying 1 resource
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ demo ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 5 source files to C:\Workspace\demo\demo\target\classes
[INFO]
[INFO] --- maven-resources-plugin:3.2.0:testResources (default-testResources) @ demo ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Using 'UTF-8' encoding to copy filtered properties files.
[INFO] skip non existing resourceDirectory C:\Workspace\demo\demo\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ demo ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to C:\Workspace\demo\demo\target\test-classes
[INFO]
[INFO] --- maven-surefire-plugin:2.22.2:test (default-test) @ demo ---
[INFO]
[INFO] -------------------------------------------------------
[INFO] T E S T S
[INFO] -------------------------------------------------------
[INFO] Running dev.michael.demo.DemoApplicationTests
... (tests omitted)
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 5.863 s - in dev.michael.demo.DemoApplicationTests
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:23 min
[INFO] Finished at: 2022-03-11T22:08:02-06:00
[INFO] ------------------------------------------------------------------------
Docker
Docker users may be familiar with the docker build command. buildx is “build extended” which is an experimental CLI command to enable the creation of platform-specific Docker images. Here’s the command I used to generate one for the 32-bit OS running on my Pis.
docker buildx build --push --platform=linux/arm/v7 --tag=michaellambgelo/demo:latest .
The output shows Docker using Buildkit. The dockerfile lets Docker know how to package and start an application container. With openjdk:8-jdk-alpine included as the container OS runtime the Spring Boot application is then pushed to the Docker registry. From the registry, the image can be downloaded to whatever Pi/Docker configuration I want.
[+] Building 38.7s (11/11) FINISHED
=> [internal] booting buildkit 1.5s
=> => starting container buildx_buildkit_magical_thompson0 1.5s
=> [internal] load build definition from Dockerfile 0.1s
=> => transferring dockerfile: 141B 0.0s
=> [internal] load .dockerignore 0.1s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/openjdk:8-jdk-alpine 3.1s
=> [auth] library/openjdk:pull token for registry-1.docker.io 0.0s
=> [internal] load build context 0.8s
=> => transferring context: 30.75MB 0.7s
=> [1/2] FROM docker.io/library/openjdk:8-jdk-alpine@sha256:94792824df2df33402f201713f932b58cb9de94a0cd524164a0f2283343547b3 7.1s
=> => resolve docker.io/library/openjdk:8-jdk-alpine@sha256:94792824df2df33402f201713f932b58cb9de94a0cd524164a0f2283343547b3 0.1s
=> => sha256:43ff02e0daa55f3a4df7eab4f7128e6b39b03ece75dfeedb53bf646fce03529c 67.40MB / 67.40MB 6.4s
=> => sha256:962e53e3f8337e63290eb26703e31f0e87d70db371afae581ad3898b1dccb972 238B / 238B 0.1s
=> => sha256:856f4240f8dba160c5323506c1e9a4dbaaca840bf1b0c244af3b8d1b42b0f43b 2.35MB / 2.35MB 0.9s
=> => pushing layers 22.4s
=> => pushing manifest for docker.io/michaellambgelo/demo:latest@sha256:87640f491f579237e378aa832614df036720da21ed0d74cbe248ba1ed6ae4acb 0.3s
=> [auth] michaellambgelo/demo:pull,push token for registry-1.docker.io 0.0s
=> [auth] michaellambgelo/demo:pull,push token for registry-1.docker.io
Future
I want to look into using Spotify Dockerfile Maven which takes an opinionated view of the Maven and Docker build processes, enabling users to combine the two build steps into one.
About michaellamb.dev
Michael Lamb is a software engineer working at C Spire. If you have a blog-specific inquiry please create a new issue on GitHub. Feel free to fork this blog and build your own!Get to know who I am in my first post Hello, World!