A Fully Integrated Device Software Update Solution

Over The Air update is a crucial topic for IoT devices, especially now that IoT is entering the realm of complex devices and industrial processes. Updating means enhanced security, enhanced functions, enhanced customer experience. It is key for innovations life cycle, be it the update of middleware or applications. Existing device software update solutions are all technically limiting or locked-in. So we made our decision:

Build a device software update solution that would freely allow any IoT maker to update their device with a simple, robust and open-source solution.

How did we do this and what where our objectives? Discover the whole story.

Remember how Docker containers has completely changed the way applications are deployed and orchestrated in the Cloud? A year ago, with a bunch of colleagues, we started imagining that we could apply the same kind of solution, with the same technologies to IoT devices instead of the cloud.

This approach would allow to organize IoT devices OTA update in a simple and robust way. So we decided to investigate if anybody had had the same idea. Through our research we came across resin.io (since then changed their name to balena) and it looked as if they offered exactly what we had in mind.

After some investigation, Resin.io, our reference for OTA update for IoT devices showed some weaknesses

After digging into the solution, we spotted out two major weaknesses:

First weakness is that this Balena solution uses the full-blown Docker stack and registries to deploy updates. The question then is how you generate containers compatible with the processor architecture you use on your IoT device on your computer (usually your computer is an Intel processor when most IoT devices use ARM processors)? The issue has been partly sorted out by providing the most usual containers (e.g., to run an application coded in Javascript) for the most usual architectures. But then, what happens if you are on something a bit unusual? You might not be able to address it with their technology and you may well get stuck with your IoT device. Which can be off course slightly annoying…

The second drawback we identified is that you, IoT maker, will have to disclose your code and give it to Balena. Their solution implies indeed, that you first need to push your source code to their git server, then they proceed to the compilation and finally push code back to your devices with the result. If you work on an open source project, this doesn’t really matter. But for quite a few innovative companies, giving away their source code is simply unthinkable.

So we came to the conclusion that IoT makers need a more flexible device software update solution for the cross compilation of applications and higher privacy for source code. And we started thinking about developing a new tool based on the same technologies.This idea eventually grew into FullMetalUpdate!

FullMetalUpdate is a fully integrated solution for simple and robust OTA updates. And it is open source! It includes everything you will need for device software update, from the embedded software to the web server. And it is easy to deploy.

Key aspects of FullMetalUpdate, The device software update solution

First of all, we decided our device software update solution would be open source. Just because OTA update is too crucial for innovators to be left in the hands of others.

It had to be open-source!

Then, we set up our expectations:

  • An update should never brick or put a device in an unknown state.
  • It should be secure, efficient and thrifty and therefore container based
  • It should work with any cloud provider.

How to reach an OTA update solution that can be used to create containers on a computer but is compatible with any IoT platform?

Yocto and containers, the perfect start to make sure we are compatible with all IoT software platforms

As you probably already know, Yocto is a good solution to build custom Linux distributions for embedded systems. A majority of processors that can run Linux are supported. Yocto tool-set is highly flexible. With some imagination and work, you can use it to generate the main image for your operating system (OS). At the same time it can also generate an independent filesystem for each application with just the right dependencies to run them. This is exactly what we call a container .But why would you put your application in container? In fact, it brings multiple benefits:

  • Security: Your application is isolated from the rest of the system. The configuration file of the container allows to finely tune what resources from the host system are accessible. In the unlikely event that an application running in a container would be hacked. It will be stuck in the container with a very limited access to the rest of the system.
  • Resource usage limitation: You can configure a container to only have a restricted access to the hardware by limiting its maximum bandwidth usage, its processor usage, its memory usage, …

Dependency isolation: Because each of your applications will be running in its own container, all issues with library incompatibilities are solved. You can have an application running with Qt4 in one container and another application using Qt5 in a different container. You will never run anymore into incompatibilities between different version of the same library.

Yocto and OCI containers

Now we had every application in a separate container, the next question was how to run these applications on an IoT device.

To make the challenge even greater we wanted our solution to be compliant with the Open Container Initiative standard.

So only 3 options were left:

First option could be RunC. It is the runtime used by Docker to run their container. This option is proven effective as it is used by basically all servers/computers running Docker.

Second option was RailCar. This runtime has been developed by Oracle. But we found out that maintenance could be an issue as the solution had not been maintained for about 7 months.

Third option available was Clearcontainers. This runtime has been developed by Intel and is leveraging the VT-x technology. But it is not compatible with ARM processors which was a clear elimination factor.

In the end, for our device software update solution, the obvious choice was RunC. It is not tied to any specific processor technology and we can be quite sure it will be maintained as the community using it is quite huge and growing.

Now that we had chosen how to build containers and decided what technology would help to run these on an embedded system, it was high time to think about how to deploy updates smartly. There, our main goal was to limit the bandwidth usage to realize an update and benefit from it’s highly appreciated side effect:limit the overall power consumption of the device. Basically, that meant we needed to realize delta updates. But what could we use to do that?

How to deploy containers from a remote host to multiple IoT devices?

FullMetalUpdate uses OSTree to Deploy containers to multiple IoT devices

One feature coming from the full-blown Docker implementation is the ability to create delta updates to limit the bandwidth usage. Docker uses specific filesystems like AUFS or Overlayfs to deal with the deltas. These solutions are great on servers but not usable on embedded systems because they are not reliable in case of power failure.

That is where OSTree came in!

OSTree generates delta updates and handles the deployment in a GIT fashion but for binaries. OSTree manages updates like git commits and generates hard links of the used commit to the filesystem. This last operation is realized atomically which guarantees data consistency. As a result, it is completely independent of the filesystem type used on the device and extremely efficient on the storage usage.

The most popular implementation of OSTree for Yocto has been designed specifically to update Linux with no separation between the operating system (OS) and the applications:

Updates with OSTree

This implementation is used by projects like ATS-Garage or the Automotive Grade Linux project.

But, one drawback is that the system needs to restart after each update. This can make sense if you update the Linux kernel, but if you update an application, it would be great to restart this specific application only after the update.

To solve this issue, we created a new OSTree repository specific to applications that will be updated independently of the rest of the system:

Update containers with OSTree

With this implementation, we had the best of two worlds.

On the one hand, we had OSTree, a solution used by multiple industrial-grade applications, to update the OS. On the other hand, we had an OSTree used to update your applications which are boxed within OCI containers (an architecture very close to the one used by Flatpak but adapted to the embedded world).

However, we were still missing one piece: The next question was how to manage the life cycle of the applications running within the different containers.

How to manage the life cycle of the applications running in the different containers?

Development of FullMetalUpdate Client

We needed a tool able to manage dependencies between the different containers. To reach this goal, we decided to develop our own software (FullMetalUpdate Client). And to avoid starting from scratch when solutions already existed, we decided to use SystemD as a back-end to manage the dependencies between the containers and to start and stop them.

How to manage and deploy our  device software updates?

Hawkbit and its challenges to build a web app in the Cloud

Next, we needed to provide a web application that could be used to manage and deploy the updates to multiple IoT devices. The obvious solution was to go for Hawkbit. Why was it so obvious? because it has the advantage of being proven effective. It is an open-source project developed by Bosh and used on numerous industrial projects.

But because our approach was based on OSTree for the deployment of updates, we faced the challenge of integrating OSTree with Hawkbit. Our solution was to push the information for the update and the reference to the OSTree commit instead of uploading the actual update package to Hawkbit. In other words, with FullMetalUpdate, you use Yocto to build the OS and your containers. Then, Yocto automatically deploys the new software version to a remote OSTree, gets the commit reference, and pushes this information to Hawkbit. Once this is done, it is up to you to use the Hawkbit UI to start updating your different IoT devices.

Of course, for all this to be possible, we still needed to create a communication layer between the IoT devices and Hawkbit. Because the FullMetalUpdate client had been developed in Python, a natural choice was to reuse parts of the RAUC project to handle the communication protocol with the Hawkbit server.

How to connect the different parts of our OTA solution together?

Docker Compose to bring everything together in your device software update

 As a last step to complete the FullMetalUpdate project, we used Docker-Compose to connect the different parts composing the server on a virtual network. To make sure that our solution will build on any computer running Docker containers, we embedded the Yocto build system within a Docker container.

We finally ended up with the architecture below:

FullMetalUpdate architecture

We now held our Grail! A fully integrated solution for OTA updates that is simple, robust and open to all.

Be ready to deploy your applications to the Edge! 

FullMetalUpdate is now available on Github and currently already includes containers to run Qt applications in full screen and neural networks using Tensor Flow Lite. This is only the beginning because the Yocto ecosystem is huge and can easily be extended to re-compile literally every project for your specific hardware!

We are actually working at some new commits that will include:

  • Full support of the Raspberry Pi 3
  • Skopeo to use containers from Docker and OCI registries
  • CNI to easily create virtual networks between your containers

And as this device software update solution is open-source, we leave it up to the community for use, optimization, growth, for the benefit of all IoT makers.

C.vincent

Ecrit par Cédric Vincent, Chief Technical Officer

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