Docker

Update Modules
1

Description

The Docker Update Module handles the Docker images that shall be running in the device. A deployment with this module will stop all currently running Docker containers in the device, and start new containers with the provided list of Docker images in the Mender Artifact.

In case of an unforeseen error during the process, the module will use the rollback mechanism of the Mender client to restore the previously running Docker containers.

Specification
Module name docker
Supports rollback yes
Requires restart no
Artifact generation script yes
Full operating system updater no
Source code Update Module, Artifact Generator
Maintainer Community

Prepare the device

This section describes how to setup your target device, i.e. the device to be updated. This will also be referred to as the device environment.

All commands outlined in this section should be run in the device environment.

Prerequisites

This update module has the following prerequisites for the device environment:

  • Install Docker Engine, version 17.03 or later.
  • A recent version of the JSON parser jq needs to be installed in the device.
  • Ensure the device has a Bash Unix shell

How to install these depends on which OS you are running.

Install the Update Module

Download the latest version of this Update Module by running:

mkdir -p /usr/share/mender/modules/v3 && wget -P /usr/share/mender/modules/v3 https://raw.githubusercontent.com/mendersoftware/mender/master/support/modules/docker

Prepare the development environment on your workstation

This section describes how to set up your development environment on your workstation.

All commands outlined in this section should be run in the development environment.

Prerequisites

This Update Module has the following prerequisites for the development environment:

Artifact creation

For convenience, an Artifact generator tool docker-artifact-gen is provided along the module. This tool will generate Mender Artifacts in the same format that the Update Module expects them.

Download docker-artifact-gen, by running the following command:

wget https://raw.githubusercontent.com/mendersoftware/mender/master/support/modules-artifact-gen/docker-artifact-gen

Make it executable:

chmod +x docker-artifact-gen

Now generate a Mender Artifact using the following command:

ARTIFACT_NAME="my-container-update-1.0"
DEVICE_TYPE="my-device-type"
OUTPUT_PATH=my-container-update-1.0.mender
DOCKER_IMAGES="docker-image-1 docker-image2"
./docker-artifact-gen -n ${ARTIFACT_NAME} -t ${DEVICE_TYPE} -o ${OUTPUT_PATH} ${DOCKER_IMAGES}
  • ARTIFACT_NAME - The name of the Mender Artifact
  • DEVICE_TYPE - The compatible device type of this Mender Artifact
  • OUTPUT_PATH - The path where to place the output Mender Artifact. This should always have a .mender suffix
  • DOCKER_IMAGES - The list of Docker images that we want the target to run. Each item can be any valid name for Docker to pull images from (tags or digests). For example debian, debian:jessie, debian:latest, debian:sha256@…, etc

Note that the actual image id that will be added in the Artifact is the digest (sha256 hash) of the image, regardless of the tag used to pull it in. This will ensure that the device will pull the exact same version of each image than the generation tool used when preparing the Artifact.

You can either deploy this Artifact in managed mode with the Mender server (upload it under Releases in the server UI) or by using the Mender client only in Standalone deployments.

Artifact technical details

The Mender Artifact used by this Update Module has no payload files. Instead it uses the Metadata field to list the Docker images, which will be downloaded by the device. This meta-data is composed by a single containers JSON key with the array of images digests to be installed in the update.

As an example, the following update will install two specific versions of Docker images debian and ubuntu:

Updates:
    0:
    Type: docker
    Provides: Nothing
    Depends: Nothing
    Metadata:
        {
            "containers": [
"debian@sha256:84e2351ae76c072adac3b6e0a958e5b238e693bdff3cc4f3c94eace3d4577f76",
"ubuntu@sha256:7a47ccc3bbe8a451b500d2b53104868b46d60ee8f5b35a24b41a86077c650210"
            ]
        }
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