Building with Chroot

Jolt can use chroot environments to provide a consistent build environment across different platforms. A chroot is typically faster to start and stop than a Docker container, but it is less isolated and secure. The chroot feature is not available on Windows.

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. When built, the image is extracted into a directory tree that is published into the task artifact.

from jolt import Chroot
from jolt.plugins.docker import DockerImage


class Alpine(DockerImage):
    dockerfile = '''
    FROM alpine:3.7
    '''

    # Extract the image into a directory tree
    extract = True

    # Dont publish the image as an archive
    imagefile = None


class AlpineChroot(Chroot):
    name = "alpine/chroot"

    # Task artifact that contains the chroot
    chroot = "alpine"

The ‘’AlpineChroot’’ class is a ‘’Chroot’’ resource that can be required by other tasks. The built directory tree chroot is automatically entered when a consumer task is executing commands. Only one chroot environment can be used by a task at a time. The workspace and the local artifact cache are mounted into the chroot environment and the current user is mapped to the chroot user.

from jolt import Task


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

    requires = ["alpine/chroot"]

    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)

A more flexible alternative to using chroots as resources is to enter the chroot environment on demand directly in the consuming task as in the example below. A task can then use multiple chroot environments at different times.

from jolt import Task


class Example2(Task):
    """ Example task that uses the alpine image to run a command. """

    requires = ["alpine"]

    def run(self, deps, tools):
        with tools.chroot(deps["alpine"]):
            tools.run("cat /etc/os-release")