What is Mender?

Mender is an open source remote software updater for embedded Linux devices. It includes both a client and a management server, which are both licensed under Apache 2.0.

It enables the management of software updates to connected devices remotely, whether over-the-air or over any TCP/IP network.

It allows you to deploy an image-based update from the server-side component of Mender to your connected device or devices. The deployment is done securely using HTTPS and the partitioned setup makes sure your device will stay up and running should anything interrupt the update process.

How it works

Mender is a client-server application, where the client is installed in embedded devices running Linux. The Mender client regularly checks with the Mender server over HTTPS to see if it has an image update available for deployment, and deploys it if there is. A dual A/B rootfs partition layout ensures robustness, so that the embedded device can recover even during incomplete or corrupted deployment installations.

Architecture

The Mender management server is now published on GitHub for on-premise installations. It is licensed under the Apache 2.0 license.

Partition layout and reliability

For reliability during the update process, Mender uses a dual A/B rootfs partition layout. The Mender client daemon runs in user space in the currently booted rootfs partition.

Installation

During the update process, the Mender client writes the updated image to the rootfs partition that is not running and configures U-Boot to boot from the updated rootfs partition. The device is then rebooted. If booting the updated partition fails, the partition that was running is booted instead, ensuring that the device does not get bricked. If the boot succeeds, Mender sets the updated partition to boot permanently when Mender starts as part of the boot process.

As Mender downloads and installs the image, other applications on the device continue to run as normal. The only time the device has downtime is during the reboot into the updated partition, which typically takes a minute, depending on the device configuration.

Persistent data can be stored in the data partition, which is left unchanged during the update process.