Docker Gradle Plugin

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

• com.palantir.docker: 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.
• com.palantir.docker-compose: adds a task for populating placeholders in a docker-compose template file with image versions resolved from dependencies.
• com.palantir.docker-run: adds tasks for starting, stopping, statusing and cleaning up a named container based on a specified image

Docker Plugin

Apply the plugin using standard gradle convention:

plugins {
    id 'com.palantir.docker' version '<version>'
}

Set the container name, and then optionally specify a Dockerfile, 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.

Docker Configuration Parameters

• name the name to use for this container, may include a tag
• tags (deprecated) (optional) an argument list of tags to create; any tag in name will be stripped before applying a specific tag; defaults to the empty set
• tag (optional) a tag to create with a specified task name
• dockerfile (optional) the dockerfile to use for building the image; defaults to project.file('Dockerfile') and must be a file object
• files (optional) an argument list of files to be included in the Docker build context, evaluated per Project#files. For example, files tasks.distTar.outputs adds the TAR/TGZ file produced by the distTar tasks, and files tasks.distTar.outputs, 'my-file.txt' adds the archive in addition to file my-file.txt from the project root directory. The specified files are collected in a Gradle CopySpec which may be copied into the Docker build context directory. The underlying CopySpec may also be used to copy entire directories into the build context. The following example adds the aforementioned archive and text file to the CopySpec, uses the CopySpec to add all files from src/myDir into the CopySpec, then finally executes the copy into the directory myDir in docker build context.

docker {
    files tasks.distTar.outputs, 'my-file.txt'
    copySpec.from("src/myDir").into("myDir")
}

The final structure will be:

build/
  docker/
    myDir/
      my-file.txt
      // contents of task.distTar.outputs
      // files from src/myDir

• buildArgs (optional) an argument map of string to string which will set --build-arg arguments to the docker build command; defaults to empty, which results in no --build-arg parameters
• labels (optional) a map of string to string which will set --label arguments to the docker build command; defaults to empty, which results in no labels applied.
• pull (optional) a boolean argument which defines whether Docker should attempt to pull a newer version of the base image before building; defaults to false
• noCache (optional) a boolean argument which defines whether Docker build should add the option --no-cache, so that it rebuilds the whole image from scratch; defaults to false
• squash (optional) a boolean argument which defines whether Docker should attempt to squash newly built layers into a single new layer; defaults to false

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

Tag and Push tasks for each tag will be generated for each provided tag and tags entry.

Examples

Simplest configuration:

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

Canonical configuration for building a Docker image from a distribution archive:

// Assumes that Gradle "distribution" plugin is applied
docker {
    name 'hub.docker.com/username/my-app:version'
    files tasks.distTar.outputs   // adds resulting *.tgz to the build context
}

Configuration specifying all parameters:

docker {
    name 'hub.docker.com/username/my-app:version'
    tags 'latest' // deprecated, use 'tag'
    tag 'myRegistry', 'my.registry.com/username/my-app:version'
    dockerfile file('Dockerfile')
    files tasks.distTar.outputs, 'file1.txt', 'file2.txt'
    buildArgs([BUILD_VERSION: 'version'])
    labels(['key': 'value'])
    pull true
    noCache true
    squash true
}

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.

The docker-compose plugin also provides a dockerComposeUp task that starts the docker images specified in the dockerComposeFile in detached mode.

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'
}

Docker Run Plugin

Apply the plugin using standard gradle convention:

plugins {
    id 'com.palantir.docker-run' version '<version>'
}

Use the dockerRun configuration block to configure the name, image and optional command to execute for the dockerRun tasks:

dockerRun {
    name 'my-container'
    image 'busybox'
    volumes 'hostvolume': '/containervolume'
    ports '7080:5000'
    daemonize true
    env 'MYVAR1': 'MYVALUE1', 'MYVAR2': 'MYVALUE2'
    command 'sleep', '100'
}

Docker Run Configuration Parameters

• name the name to use for this container, may include a tag.
• image the name of the image to use.
• volumes optional map of volumes to mount in the container. The key is the path to the host volume, resolved using project.file(). The value is the exposed container volume path.
• ports optional mapping local:container of local port to container port.
• env optional map of environment variables to supply to the running container. These must be exposed in the Dockerfile with ENV instructions.
• daemonize defaults to true to daemonize the container after starting. However if your container runs a command and exits, you can set this to false.
• clean (optional) a boolean argument which adds --rm to the docker run command to ensure that containers are cleaned up after running; defaults to false
• command the command to run.

Tasks

• Docker
  • docker: build a docker image with the specified name and Dockerfile
  • dockerTag: tag the docker image with all specified tags
  • dockerTag<tag>: tag the docker image with <tag>
  • dockerPush: push the specified image to a docker repository
  • dockerPush<tag>: push the <tag> docker image to a docker repository
  • dockerTagsPush: push all tagged docker images to a docker repository
  • dockerPrepare: prepare to build a docker image 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
• Docker Compose
  • generateDockerCompose: Populates a docker-compose file template with image versions declared by dependencies
  • dockerComposeUp: Brings up services defined in dockerComposeFile in detacted state
• Docker Run
  • dockerRun: run the specified image with the specified name
  • dockerStop: stop the running container
  • dockerRunStatus: indicate the run status of the container
  • dockerRemoveContainer: remove the container

License

This plugin is made available under the Apache 2.0 License.

Contributing

Contributions to this project must follow the contribution guide.