Thursday, July 19, 2018

Jib - Building docker image for a Spring Boot App

I was pleasantly surprised by how easy it was to create a docker image for a sample Spring Boot application using Jib.

Let me first contrast Jib with an approach that I was using before.

I was creating docker images using bmuschko's excellent gradle-docker plugin. Given access to a docker daemon and a gradle dsl based description of the Dockerfile or a straight Dockerfile, it would create the docker image using a gradle task. In my case, the task to create the docker image looks something like this:

task createDockerImage(type: DockerBuildImage) {
    inputDir = file('.')
    dockerFile = project.file('docker/Dockerfile')
    tags = ['sample-micrometer-app:' + project.version]

createDockerImage.dependsOn build

and my Dockerfile itself derived off "java:8" base image:

FROM java:8

gradle-docker-plugin made it simple to create a docker image right from gradle with the catch that the plugin needs access to a docker daemon to create the image. Also since the base "java:8" image is large the final docker image turns out to be around 705MB on my machine. Again no fault of the gradle-docker plugin but based on my choice of base image.

Now with Jib, all I have to do is to add the plugin:

plugins {
    id '' version '0.9.6'

Configure it to give the image a name:

jib {
    to {
        image = "sample-micrometer-app:0.0.1-SNAPSHOT"

And that is it. With a local docker daemon available, I can create my docker image using the following task:

./gradlew jibDockerBuild

Jib automatically selects a very lightweight base image - my new image is just about 150 MB in size.

If I had access to a docker registry available then the local docker daemon is not required, it can directly create and publish the image to a docker registry!

Jib gradle plugin provides an interesting task - "jibExportDockerContext" to export out the docker file, this way if needed a docker build can be run using this Dockerfile, for my purposes I wanted to see the contents of this file and it looks something like this:


COPY libs /app/libs/
COPY resources /app/resources/
COPY classes /app/classes/

ENTRYPOINT ["java","-cp","/app/libs/*:/app/resources/:/app/classes/","sample.meter.SampleServiceAppKt"]

All in all, a very smooth experience and Jib does live up to its goals. My sample project with jib integrated with a gradle build is available here.

No comments:

Post a Comment