docker-maven-plugin
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INACTIVE: A maven plugin for Docker
docker-maven-plugin
A Maven plugin for building and pushing Docker images.
Status: inactive
We recommend you use dockerfile-maven instead.
The future of docker-maven-plugin
This plugin was the initial Maven plugin used at Spotify for building Docker
images out of Java services. It was initially created in 2014 when we first
began experimenting with Docker. This plugin is capable of generating a
Dockerfile
for you based on configuration in the pom.xml file for things like
the FROM
image, resources to add with ADD
/COPY
, etc.
Over time at Spotify we have realized that the simplest way to build a Docker
image from a Java project is to have the developer write the Dockerfile
. The
behavior of this plugin around generating Dockerfiles, copying your project
directory to a "staging" directory to use as the Docker build context, etc.,
ultimately led to a lot of unnecessary confusion with our users that stemmed
from introducing extra abstractions and a need for configuration on top of what
Docker is providing.
This led to the creation of a second Maven plugin for building docker images, dockerfile-maven, which we think offers a simpler mental model of working with Docker from Maven, for all of the reasons outlined in dockerfile-maven's README.
- The future of docker-maven-plugin
- Purpose
-
Setup
- Specify build info in the POM
- Use a Dockerfile
-
Usage
- Bind Docker commands to Maven phases
- Using with Private Registries
-
Authentication
- Using encrypted passwords for authentication
- Testing
- Releasing
- Known Issues
Purpose
You can use this plugin to create a Docker image with artifacts built from your Maven project. For example, the build process for a Java service can output a Docker image that runs the service.
Setup
You can specify the base image, entry point, cmd, maintainer and files you want to add to your
image directly in the pom, without needing a separate Dockerfile
.
If you need VOLUME
command(or any other not supported dockerfile command), then you will need
to create a Dockerfile
and use the dockerDirectory
element.
By default the plugin will try to connect to docker on localhost:2375. Set the DOCKER_HOST environment variable to connect elsewhere.
DOCKER_HOST=tcp://<host>:2375
Other docker-standard environment variables are honored too such as TLS and certificates.
Specify build info in the POM
This example creates a new image named example
, copies the project's jar file into the image,
and sets an entrypoint which runs the jar. Change VERSION GOES HERE
to the latest tagged version.
<build>
<plugins>
...
<plugin>
<groupId>com.spotify</groupId>
<artifactId>docker-maven-plugin</artifactId>
<version>VERSION GOES HERE</version>
<configuration>
<imageName>example</imageName>
<baseImage>java</baseImage>
<entryPoint>["java", "-jar", "/${project.build.finalName}.jar"]</entryPoint>
<!-- copy the service's jar file from target into the root directory of the image -->
<resources>
<resource>
<targetPath>/</targetPath>
<directory>${project.build.directory}</directory>
<include>${project.build.finalName}.jar</include>
</resource>
</resources>
</configuration>
</plugin>
...
</plugins>
</build>
Use a Dockerfile
To use a Dockerfile
, you must specify the dockerDirectory
element. If specified, the
baseImage
, maintainer
, cmd
and entryPoint
elements will be ignored. The contents of the
dockerDirectory
will be copied into ${project.build.directory}/docker
. Use the resources
element to copy additional files, such as the service's jar file.
<build>
<plugins>
...
<plugin>
<groupId>com.spotify</groupId>
<artifactId>docker-maven-plugin</artifactId>
<version>VERSION GOES HERE</version>
<configuration>
<imageName>example</imageName>
<dockerDirectory>docker</dockerDirectory>
<resources>
<resource>
<targetPath>/</targetPath>
<directory>${project.build.directory}</directory>
<include>${project.build.finalName}.jar</include>
</resource>
</resources>
</configuration>
</plugin>
...
</plugins>
</build>
Usage
You can build an image with the above configurations by running this command.
mvn clean package docker:build
To push the image you just built to the registry, specify the pushImage
flag.
mvn clean package docker:build -DpushImage
To push only specific tags of the image to the registry, specify the pushImageTag
flag.
mvn clean package docker:build -DpushImageTag
In order for this to succeed, at least one imageTag must be present in the config, multiple tags can be used.
<build>
<plugins>
...
<plugin>
<configuration>
...
<imageTags>
<imageTag>${project.version}</imageTag>
<imageTag>latest</imageTag>
</imageTags>
</configuration>
</plugin>
...
</plugins>
</build>
Optionally, you can force docker to overwrite your image tags on each new build:
<build>
<plugins>
...
<plugin>
<configuration>
...
<!-- optionally overwrite tags every time image is built with docker:build -->
<forceTags>true</forceTags>
<imageTags>
...
</imageTags>
</configuration>
</plugin>
...
</plugins>
</build>
Tags-to-be-pushed can also be specified directly on the command line with
mvn ... docker:build -DpushImageTag -DdockerImageTags=latest,another-tag
Bind Docker commands to Maven phases
You can also bind the build, tag & push goals to the Maven phases, so the container will be built, tagged and pushed
when you run just mvn deploy
. If you have a multi-module project where a sub-module builds an image, you
will need to do this binding so the image gets built when maven is run from the parent project.
<plugin>
<groupId>com.spotify</groupId>
<artifactId>docker-maven-plugin</artifactId>
<version>VERSION GOES HERE</version>
<executions>
<execution>
<id>build-image</id>
<phase>package</phase>
<goals>
<goal>build</goal>
</goals>
</execution>
<execution>
<id>tag-image</id>
<phase>package</phase>
<goals>
<goal>tag</goal>
</goals>
<configuration>
<image>my-image:${project.version}</image>
<newName>registry.example.com/my-image:${project.version}</newName>
</configuration>
</execution>
<execution>
<id>push-image</id>
<phase>deploy</phase>
<goals>
<goal>push</goal>
</goals>
<configuration>
<imageName>registry.example.com/my-image:${project.version}</imageName>
</configuration>
</execution>
</executions>
</plugin>
You can skip Docker goals bound to Maven phases with:
-
-DskipDockerBuild
to skip image build -
-DskipDockerTag
to skip image tag -
-DskipDockerPush
to skip image push -
-DskipDocker
to skip any Docker goals
To remove the image named foobar
run the following command:
mvn docker:removeImage -DimageName=foobar
For a complete list of configuration options run:
mvn com.spotify:docker-maven-plugin:<version>:help -Ddetail=true
Using with Private Registries
To push an image to a private registry, Docker requires that the image tag
being pushed is prefixed with the hostname and port of the registry. For
example to push my-image
to registry.example.com
, the image needs to be
tagged as registry.example.com/my-image
.
The simplest way to do this with docker-maven-plugin is to put the registry
name in the <imageName>
field, for example
<plugin>
<groupId>com.spotify</groupId>
<artifactId>docker-maven-plugin</artifactId>
<configuration>
<imageName>registry.example.com/my-image</imageName>
...
Then when pushing the image with either docker:build -DpushImage
or
docker:push
, the docker daemon will push to registry.example.com
.
Alternatively, if you wish to use a short name in docker:build
you can use
docker:tag -DpushImage
to tag the just-built image with the full registry
hostname and push it. It's important to use the pushImage
flag as using
docker:push
independently will attempt to push the original image.
For example:
<plugin>
<groupId>com.spotify</groupId>
<artifactId>docker-maven-plugin</artifactId>
<configuration>
<imageName>my-image</imageName>
...
</configuration>
<executions>
<execution>
<id>build-image</id>
<phase>package</phase>
<goals>
<goal>build</goal>
</goals>
</execution>
<execution>
<id>tag-image</id>
<phase>package</phase>
<goals>
<goal>tag</goal>
</goals>
<configuration>
<image>my-image</image>
<newName>registry.example.com/my-image</newName>
</configuration>
</execution>
</executions>
</plugin>
Authentication
Since version 1.0.0, the docker-maven-plugin will automatically use any
authentication present in the docker-cli configuration file at ~/.dockercfg
or ~/.docker/config.json
, without the need to configure anything (in earlier
versions of the plugin this behavior had to be enabled with
<useConfigFile>true</useConfigFile>
, but now it is always active).
Additionally the plugin will enable support for Google Container Registry if it
is able to successfully load Google's "Application Default Credentials".
The plugin will also load Google credentials from the file pointed to by the
environment variable DOCKER_GOOGLE_CREDENTIALS
if it is defined. Since GCR
authentication requires retrieving short-lived access codes for the given
credentials, support for this registry is baked into the underlying
docker-client rather than having to first populate the docker config file
before running the plugin.
Lastly, authentication credentials can be explicitly configured in your pom.xml
and in your Maven installation's settings.xml
file as part of the
<servers></servers>
block.
<servers>
<server>
<id>docker-hub</id>
<username>foo</username>
<password>secret-password</password>
<configuration>
<email>[email protected]</email>
</configuration>
</server>
</servers>
Now use the server id in your project pom.xml
.
<plugin>
<plugin>
<groupId>com.spotify</groupId>
<artifactId>docker-maven-plugin</artifactId>
<version>VERSION GOES HERE</version>
<configuration>
[...]
<serverId>docker-hub</serverId>
<registryUrl>https://index.docker.io/v1/</registryUrl>
</configuration>
</plugin>
</plugins>
The plugin gives priority to any credentials in the docker-cli config file before explicitly configured credentials.
Using encrypted passwords for authentication
Credentials can be encrypted using Maven's built in encryption function. Only passwords enclosed in curly braces will be considered as encrypted.
<servers>
<server>
<id>docker-hub</id>
<username>foo</username>
<password>{gc4QPLrlgPwHZjAhPw8JPuGzaPitzuyjeBojwCz88j4=}</password>
</server>
</servers>
Testing
Make sure Docker daemon is running and that you can do docker ps
. Then run mvn clean test
.
Releasing
Commits to the master branch will trigger our continuous integration agent to build the jar and release by uploading to Sonatype. If you are a project maintainer with the necessary credentials, you can also build and release locally by running the below.
mvn release:clean
mvn release:prepare
mvn release:perform
Known Issues
Exception caught: system properties: docker has type STRING rather than OBJECT
Because the plugin uses Maven properties named like
docker.build.defaultProfile
, if you declare any other Maven property with the
name docker
you will get a rather strange-looking error from Maven:
[ERROR] Failed to execute goal com.spotify:docker-maven-plugin:0.0.21:build (default) on project <....>:
Exception caught: system properties: docker has type STRING rather than OBJECT
To fix this, rename the docker
property in your pom.xml.
InternalServerErrorException: HTTP 500 Internal Server Error
Problem: when building the Docker image, Maven outputs an exception with a stacktrace like:
Caused by: com.spotify.docker.client.shaded.javax.ws.rs.InternalServerErrorException: HTTP 500 Internal Server Error
docker-maven-plugin communicates with your local Docker daemon using the HTTP
Remote API and any unexpected errors that the daemon encounters will be
reported as 500 Internal Server Error
.
Check the Docker daemon log (typically at /var/log/docker.log
or
/var/log/upstart/docker.log
) for more details.
Invalid repository name ... only [a-z0-9-_.] are allowed
One common cause of 500 Internal Server Error
is attempting to build an image
with a repository name containing uppercase characters, such as if the
<imageName>
in the plugin's configuration refers to ${project.version}
when
the Maven project version is ending in SNAPSHOT
.
Consider putting the project version in an image tag (instead of repository
name) with the <dockerImageTags>
configuration option instead.