Add local storage to Azure IoT Edge modules using Docker Bind

Azure IoT Edge makes use of the Moby container runtime so IoT Edge modules (being Docker containers) can work together and offer logic on the edge.

Docker containers are ‘sandboxed’. This means that the logic within the containers has limited access to the environment they ‘live’ in.

By default, containers have no SUDO rights, no access to the host filesystem, and just limited network capabilities.

Though, containers can be granted elevated rights. One of these is the right to access the filesystem.

In this blog, we will see how to configure a container with access to the filesystem. To demonstrate this, a custom IoT Edge module is introduced, an IoT Edge filewatcher for CSV files:

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Add rolling logging to your Moby containers

Recently we were testing Azure IoT Edge on VMs which were limited in size. All went well, everything worked as expected until the whole solution stopped working.

After some research, we found out the VM disk was full of data.
This came to us as a surprise. What was eating up the hard disk?

After some more research, we checked out the Azure IoT Edge modules logging location: /var/lib/docker/containers/

Here you find folders, one for each container on your system. These are named after a unique GUID which is related to a specific container.

Note: you might need elevated rights to actually access these folders.

You can compare the folder GUID with the container ID in:

docker ps

If you open one of these folders you will find the logging of the related container.

We can, of course, remove the old logging by removing the files and everything seems to be working again. But that only delays the inevitable.

Let’s see if there is a more permanent solution.