7.3.10.3. Gradle Plugin for Docker

In this section, we cover the building and pushing the Docker images into the single Uber JAR using Gradle.

There are many Gradle plugins for Docker. We are going to use the bmuschko/gradle-docker-plugin.

In the build.gradle file import the necessary classes for managing images and add the buildscript dependency on the plugin:

buildscript {

    dependencies {
        classpath 'com.bmuschko:gradle-docker-plugin:X.Y.Z'
    }
}

import com.bmuschko.gradle.docker.tasks.image.Dockerfile
import com.bmuschko.gradle.docker.tasks.image.DockerBuildImage
import com.bmuschko.gradle.docker.tasks.image.DockerPushImage
import com.bmuschko.gradle.docker.DockerRegistryCredentials

The plugin com.bmuschko.docker-remote-api allows interacting with Docker via its remote API. You can model any workflow imaginable by creating enhanced task of the custom task provided by the plugin. To use the plugin, include the following code snippet in your build script:

apply plugin: 'com.bmuschko.docker-remote-api'

A Dockerfile can be created by the Dockerfile custom tasks. The Dockerfile instructions need to be declared in the correct order.

task createDockerfile(type: Dockerfile, dependsOn: buildUberJar)  {
    destFile = project.file('build/distributions/uberJar/Dockerfile')
    from 'openjdk:8'
    addFile("app.jar", "/usr/src/cuba-sales/app.jar")
    defaultCommand("java", "-Dapp.home=/usr/src/cuba-sales/home", "-jar", "/usr/src/cuba-sales/app.jar")
}

  • from property adds the base Docker image used during building images.

  • addFile property defines the path to the source JAR that will be copied to the image. Note, that the source JAR should be in the same folder as the Dockerfile.

  • defaultCommand property defines the command for running the application.

Image pull or push operations against the public Docker Hub registry or a private registry may require authentication. You can provide your credentials with the registryCredentials closure. Set your credentials in the gradle.properties file:

dockerHubEmail = 'example@email.com'
dockerHubPassword = 'docker-hub-password'
dockerHubUsername = 'docker-hub-username'

You can access a project property in your build script simply by using its name as you would use a variable:

def dockerRegistryCredentials = new DockerRegistryCredentials()
dockerRegistryCredentials.email = dockerHubEmail
dockerRegistryCredentials.password = dockerHubPassword
dockerRegistryCredentials.username = dockerHubUsername

Define the following tasks to build a Docker image from a Dockerfile and to push this image to the public Docker Hub registry:

task buildImage(type: DockerBuildImage, dependsOn: createDockerfile) {
    inputDir = createDockerfile.destFile.parentFile
    tags = ['sample-sales', '{docker-hub-username}/{default-repo-folder-name}:sample-sales']
    registryCredentials = dockerRegistryCredentials
}

task pushImage(type: DockerPushImage, dependsOn: buildImage) {
    tag = 'sample-sales'
    imageName = '{docker-hub-username}/{default-repo-folder-name}'
    registryCredentials = dockerRegistryCredentials
}

Set up the single Uber JAR as it is described in the Single Uber JAR Deployment section. Then run the pushImage task from the terminal or from the Search field in Studio.

gradle pushImage

This task successively builds Uber JAR, generates the Dockerfile, builds the image and pushes this image to your Docker Hub registry.