Imagine that you have a large fleet of devices, all needing a full filesystem update. Furthermore, assume that most of the image is unchanged from the previous release; i.e.: the number of bytes actually changed between the two images constitutes a very small fraction of total image size. Deploying the complete filesystem image to all the devices takes considerable time and bandwidth, even though we know that the delta between them is relatively small. To address this issue you can use binary delta update Artifacts that pass only the difference between the two images.
To generate binary delta Artifacts, you must start with two full file system Artifacts. You can use Yocto, mender-convert, or any mechanism of your choice to create the images. You can generate a binary default Artifact with the following command.
./mender-binary-delta-generator \ -o v2.0-deltafrom-v1.0.mender \ release-v.1.0.mender release-v.2.0.mender
In the above we have assumed that the current working directory contains at least:
$ ls -1 mender-binary-delta-generator release-v.1.0.mender release-v.2.0.mender
mender-binary-delta-generator application coming from mender-binary-delta archive which you need to download.
You can now use
v2.0-deltafrom-v1.0.mender with Mender, and the Client will
automatically detect its type and handle it appropriately.
The above approach can save considerable time and bandwidth, but it requires read-only root filesystem support to ensure that the delta calculated offline will apply properly to the active root filesystem. Please refer to the Mender Hub for more information on how to incorporate the binary Delta update Artifacts into your build.
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