Swarm Mode

Still my favourate way to run a cluster of Docker hosts. Fast any easy to set up and scales well for simple moderate loads.

Swarm mode on Raspberry Pi Computers

I run a tiny cluster all my own. It is a cluster of 3 Raspberry Pi 4 single board computers (the 8GB version) house in a Pico 3 case.

I run CapRover to make the deployment process super easy. Check it out if you have not seen it before.

I recently rebuilt my cluster with Ubuntu 22.04 as the base OS and hit a snag. Installing docker and creating a swarm was fine, but as soon as I tried to spin up any services they constantly failed to start up with the error:

subnet sandbox join failed for "10.0.0.0/24": error creating vxlan interface: operation not supported

It took a bit of digging but this is due to missing features in the default Kernel shipped with Ubuntu for the Raspberry Pi. I presume to keep the kernal small for this somewhat limited device. Support for VXLANs specifically.

Fortunately the solution is actually quite simple. You need to install some extra modules specifically for the Pi:

sudo apt install linux-modules-extra-raspi

Once this was installed, and the machine rebooted it services in Docker Swarm worked fine again.