Building with Docker

Jolt can use Docker containers to provide a consistent build environment across different platforms. The example task below creates a Docker image based on the Alpine Linux distribution. The Dockerfile is defined in the task class. It can also be defined in a separate file and pointed to by the dockerfile attribute.

from jolt.plugins.docker import DockerImage


class Alpine(DockerImage):
    dockerfile = '''
    FROM alpine:3.7
    RUN apk add --no-cache python3
    '''

The Docker image is built using the jolt build command. The image is tagged with the name of the task and its hash identity and saved to a file that is published into the task artifact.

$ jolt build alpine

The image can then be used to create a container that is used as a chroot environment when executing tasks. The required image file is automatically loaded from the artifact cache when the container is created. The workspace and the local artifact cache are mounted into the container and the current user is mapped to the container user.

from jolt.plugins.docker import DockerContainer


class AlpineContainer(DockerContainer):
    name = "alpine/container"

    # The image to use for the container.
    # This is either a task name or a full image name.
    image = "alpine"

    # Mark the container as a chroot container.
    # Consumer tasks will run all commands in the container.
    chroot = True

The container is used as a resource by other tasks which means that the container is automatically started and stopped when a consumer task is executed. Only one container can be used by a task at a time.

from jolt import Task


class Example(Task):
    """ Example task that uses the alpine/container to run a command. """

    requires = ["alpine/container"]

    def run(self, deps, tools):
        tools.run("cat /etc/os-release")

$ jolt build task

[   INFO] Execution started (example d6058305)
NAME="Alpine Linux"
ID=alpine
VERSION_ID=3.7.3
PRETTY_NAME="Alpine Linux v3.7"
HOME_URL="http://alpinelinux.org"
BUG_REPORT_URL="http://bugs.alpinelinux.org"
[   INFO] Execution finished after 00s (example d6058305)