Docker Gradle Plugin

This repository provides two Gradle plugins for working with Docker containers:

The com.palantir.docker plugin add basic tasks for building and pushing docker images based on a simple configuration block that specifies the container name, the Dockerfile, task dependencies, and any additional file resources required for the Docker build.
The com.palantir.docker-compose plugin adds a task for populating placeholders in a docker-compose template file with image versions resolved from dependencies.

Docker Plugin

Usage

Apply the plugin using standard gradle convention:

plugins {
    id 'com.palantir.docker'
}

Set the container name, and then optionally specify a Dockerfile path, any task dependencies and file resources required for the Docker build. This plugin will automatically include outputs of task dependencies in the Docker build context.

Examples

Simplest configuration:

docker {
    name 'hub.docker.com/username/my-app:version'
}

Configuration specifying all parameters:

docker {
    name 'hub.docker.com/username/my-app:version'
    dockerfile 'Dockerfile'
    dependsOn tasks.distTar
    files 'file1.txt', 'file2.txt'
}

To build a docker container, run the docker task. To push that container to a docker repository, run the dockerPush task.

Managing Docker image dependencies

The com.palantir.docker and com.palantir.docker-compose plugins provide functionality to declare and resolve version-aware dependencies between docker images. The primary use-case is to generate docker-compose.yml files whose image versions are mutually compatible and up-to-date in cases where multiple images depend on the existence of the same Dockerized service.

Specifying and publishing dependencies on Docker images

The docker plugin adds a docker Gradle component and a docker Gradle configuration that can be used to specify and publish dependencies on other Docker containers.

Example

plugins {
    id 'maven-publish'
    id 'com.palantir.docker'
}

...

dependencies {
    docker 'foogroup:barmodule:0.1.2'
    docker project(":someSubProject")
}

publishing {
    publications {
        dockerPublication(MavenPublication) {
            from components.docker
            artifactId project.name + "-docker"
        }
    }
}

The above configuration adds a Maven publication that specifies dependencies on barmodule and the someSubProject Gradle sub project. The resulting POM file has two dependency entries, one for each dependency. Each project can declare its dependencies on other docker images and publish an artifact advertising those dependencies.

Generating docker-compose.yml files from dependencies

The com.palantir.docker-compose plugin uses the transitive dependencies of the docker configuration to populate a docker-compose.yml.template file with the image versions specified by this project and all its transitive dependencies. The plugin uses standard Maven/Ivy machanism for declaring and resolving dependencies.

The generateDockerCompose task generates a docker-compose.yml file from a user-defined template by replacing each version variable by the concrete version declared by the transitive dependencies of the docker configuration. The task performs two operations: First, it generates a mapping group:name --> version from the dependencies of the docker configuration (see above). Second, it replaces all occurrences of version variables of the form {{group:name}} in the docker-compose.yml.template file by the resolved versions and writes the resulting file as docker-compose.yml.

Example

Assume a docker-compose.yml.template as follows:

myservice:
  image: 'repository/myservice:latest'
otherservice:
  image: 'repository/otherservice:{{othergroup:otherservice}}'

build.gradle declares a dependency on a docker image published as 'othergroup:otherservice' in version 0.1.2:

plugins {
    id 'com.palantir.docker-compose'
}

dependencies {
    docker 'othergroup:otherservice:0.1.2'
}

The generateDockerCompose task creates a docker-compose.yml as follows:

myservice:
  image: 'repository/myservice:latest'
otherservice:
  image: 'repository/otherservice:0.1.2'

The generateDockerCompose task fails if the template file contains variables that cannot get resolved using the provided docker dependencies. Version conflicts between transitive dependencies of the same artifact are handled with the standard Gradle semantics: each artifact is resolved to the highest declared version.

Configuring file locations

The template and generated file locations are customizable through the dockerCompose extension:

dockerCompose {
    template 'my-template.yml'
    dockerComposeFile 'my-docker-compose.yml'
}

Tasks

docker: build a docker container with the specified name and Dockerfile
dockerPush: push the specified container to a docker repository
dockerPrepare: prepare to build a docker container by copying dependent task outputs, referenced files, and dockerfile into a temporary directory
dockerClean: remove temporary directory associated with the docker build
dockerfileZip: builds a ZIP file containing the configured Dockerfile
generateDockerCompose: Populates a docker-compose file template with image versions declared by dependencies

License

This plugin is made available under the Apache 2.0 License.

imranity/gradle-docker