Docker Wrapper

Edit page Last modified: 28 March 2022

The Docker Wrapper extension allows running a build step inside the specified Docker image.

The extension is available for the following build runners:

Each of the supported runners has the dedicated Docker settings section.

tip

Docker Wrapper is a part of the TeamCity-Docker integration toolset. Refer to this page for information on software requirements, supported environments, and other common aspects of this integration.

Docker Settings

In the Docker Settings section of the build step settings, you can specify a Docker image which will be used to run the build step. Once the image is specified, the following options become available.

Setting

Description

Run step within Docker container

Specify a Docker image name as stated in Docker Hub. TeamCity will start a container from the specified image and will try to run this build step within this container.

For example, ruby:2.4 will run the step within the Ruby container, version 2.4.

Docker image platform

Select <Any> (default), Linux, or Windows.

Pull image explicitly

If enabled, the image will be pulled from the Hub repository via docker pull <imageName> before the docker run command is launched.

Additional docker run arguments

Allows specifying additional options for the docker run command. The default argument is --rm, but you can provide more, for instance, add an additional volume mapping.

tip

In this field, you cannot reference environment variables using the %env.FOO_BAR% syntax because TeamCity does not pass environment variables from a build agent into a Docker container.
If you need to reference an environment variable on an agent, define the configuration parameter system.FOO_BAR=env_var_value in buildAgent.properties and reference it via %system.FOO_BAR%.

How Docker Wrapper Works

Technically, the command of the build runner is wrapped in a shell script, and this script is executed inside a Docker container with the docker run command. All the details about the started process, text of the script, and so on, are written into the build log (the Verbose mode enables viewing them).

The Docker wrapper maps paths to the build checkout directory and other agent directories like buildAgent/work, so that all these directories have the same location on a build agent and inside a Docker wrapper.

If the process environment contains the TEAMCITY_DOCKER_NETWORK environment variable set by the previous Docker Compose build step, this network is passed to the started docker run command with the --network switch.

Restoring File Ownership on Linux

At the end of each build step performed inside a Docker wrapper, a build agent runs the chown command to restore the access of the buildAgent user to the checkout directory. This is done to prevent a potential problem when the files from a Docker container are created with the root ownership and cannot be removed by the build agent later.

By default, a TeamCity agent uses the busybox image from Docker Hub to run the chown command. You can specify an alternative image name with the teamcity.internal.docker.busybox parameter, either in the buildAgent.properties file or in the build configuration parameters.

tip

You may want to disable restoring the file ownership. For instance, if the userns-remap package is used for handling ownership of files created under Docker. For this, add the teamcity.docker.chown.enabled=false configuration parameter to the buildAgent.properties file. As a result, TeamCity will not try to restore permissions of the files at the end of the build.

Environment Variables Handling

TeamCity passes environment variables from the build configuration into the Docker process, but it does not pass environment variables from the build agent, as they may not be relevant to the Docker container environment. The list of the passed environment variables can be seen in the Verbose mode in the build log.

Setting Image Entrypoint

If a Docker image does not define an ENTRYPOINT, you can use still run a container with an ENTRYPOINT from the command line:

  1. Add a Command Line build step.

  2. Set the Run mode to Executable with parameters.

  3. In the Command executable field, specify the full path to the ENTRYPOINT in the target Docker container.

  4. In Docker Settings, specify the name of the Docker container.

TeamCity will start the specified Docker image with the defined ENTRYPOINT.

See also

Administrator's Guide