Deploy a system update

tutorial

This tutorial will walk you trough how to do robust system level updates with rollback. These type of updates cover the whole system including system level applications and the Linux kernel and ensure the device comes back in a consistent state even if the update process is interrupted for any reason such as power loss.

Prerequisites

You should:

Step 1 - Download the mender-artifact utility on your workstation

Prepare destination directory:

mkdir -p ${HOME}/bin

Download the mender-artifact binary

wget https://d1b0l86ne08fsf.cloudfront.net/mender-artifact/3.4.0/linux/mender-artifact -O ${HOME}/bin/mender-artifact

Make the mender-artifact binary executable:

chmod +x ${HOME}/bin/mender-artifact

Add ${HOME}/bin to PATH:

export PATH="${PATH}:${HOME}/bin"

Add above to ~/.bashrc or equivalent to make it persistent across multiple terminal sessions.

Step 2 - Setup shell variables on your workstation

Setup the IP_ADDRESS shell variable with correct IP address of your device:

IP_ADDRESS="<DEVICE-IP-ADDRESS>"

Setup USER environment variable to match an existing user on the device, e.g for Raspberry Pi devices:

USER="pi"

Use USER="root" if you are using a virtual device

Mender Artifact's require a device compatibility value as input, which must match what the device is reporting to the Mender server or it will refuse to install it. This is a safety mechanism to avoid installing software to incompatible hardware.

If you are unsure, you can check what the device is reporting on the server:

connecting a device

Use the result from above to assign that value to DEVICE_TYPE shell variable:

DEVICE_TYPE="raspberrypi4"

Make sure to replace raspberrypi4 with the specific value that you are seeing in your setup

Set SSH_ARG shell variable to specify the SSH access port:

SSH_ARG="-p 22"

If you are using a virtual device use SSH_ARG="-p 8822"

Step 3 - Create a Mender Artifact using the snapshot feature

The easiest way to create system level updates is to use the snapshot functionality in Mender, which will create a snapshot of the full system on a currently running device and package it as a Mender Artifact that you can deploy to other devices.

Run the following command on your workstation to generate a snapshot Mender Artifact from your device:

mender-artifact write rootfs-image \
    -f ssh://"${USER}@${IP_ADDRESS}" \
    -t "${DEVICE_TYPE}" \
    -n system-v1 \
    -o system-v1.mender \
    -S "${SSH_ARG}"

Your device is not usable while the snapshot operation is in progress. Mender will freeze the storage device during this operation in order to create a consistent snapshot.

Depending on your local network and storage speed, this will take up to 10-20 minutes to finish. You will see a progress indicator, and when it reaches 100% it will package the Mender Artifact which will take a few more minutes because it will need to compress the snapshot image.

The end result is a file called system-v1.mender. Upload this file to hosted Mender. You can do that using the UI under the Releases tab, as demonstrated below.

connecting a device

Step 4 - Modify the device software

While your Artifact is uploading we make some modifications to the device so we can see the effect of the deployment later. On your device, run the following command to install a text editor:

sudo apt update && sudo apt install vim --assume-yes

You can now run vim to verify it is installed, as you would expect. Note that this modification is not part of your system snapshot created above.

Step 5 - Deploy the snapshot and experiment

Once the Artifact upload in Step 3 has finished, go to the DEPLOYMENTS tab and click CREATE DEPLOYMENT in order to deploy it to your device.

Once this deployment finishes it will have the effect of restoring your full device root file system to the same state as when you created the snapshot in Step 3. You can verify this by trying to run vim again after the deployment has finished. It is gone! This is because your device file system did not have this application at the time you created the snapshot. This works for any change in the file system, including removing or installing software and changing any configuration.

Please take a moment to experiment at this stage to familiarize yourself with robust system updates with Mender.

As an example you can iterate this flow:

  1. Make a change on the device, e.g change a configuration file or install an application.
  2. Create a snapshot of the device changes you made

    Mender will skip a deployment to a device if the Artifact is already installed, in order to limit resource usage, downtime and ensure consistency across the fleet. Make sure to use different names for new Artifacts you generate (instead of the two instances of system-v1 above).

  3. Upload the generated Artifact (.mender) to hosted Mender and deploy it.
  4. Once you have two or more Artifacts uploaded you can switch between the software you have on your devices by deploying the respective Artifacts.

Deploy to many devices in order to effectively replicate the device software and configuration.

To read more about system snapshots see the documentation on Artifact from system snapshot.

Using the snapshot feature is one way to create system updates and additional resources on more advanced ways you will find here:

  1. Building a Mender Yocto Project image
  2. Building a Mender Debian image

Next step

Proceed to Deploy a Docker container update.

Found errors? Think you can improve this documentation? Simply click the Edit link at the top of the page, and then the icon on Github to submit changes.