This is a docker swarm on a cluster of raspberry pi’s running OpenFaaS. FaaS stands for Functions as a Service, from Wikipedia it is “a category of cloud computing services that provides a platform allowing customers to develop, run, and manage application functionalities without the complexity of building and maintaining the infrastructure typically associated with developing and launching an app.” Allowing developers to execute code in response to events without having to build out the typical infrastructure.
From Alex Ellis the creator of OpenFaas, “The idea is to make it as simple possible to create a function that is built for, deployed to and run on Docker Swarm or Kubernetes, while providing a workflow that integrates directly with the Docker ecosystem.”
This allows us to turn anything into a serverless function that runs through Docker Swarm on Linux or Windows. It allows us to upload functions, modular chunks of code, into the cloud and execute independently.
The Pimoroni Blinkt LED’s on the raspberry’s allow for a visual display of the load on each, above is a demo of this scaling up.
Below is a demo of the LED’s showing a rolling update.
And then scaling the service back down to zero.
Headless Raspberry Pi setup
A headless setup allows us to use the raspberry over the network without a monitor, keyboard or mouse. We can install a more lightweight operating system without a GUI (graphical user interface). Saving on hardware costs and the machines resources. The headless Linux install I’m using is based on Debian and designed specifically for Raspberry Pi hardware. You can download it here:
https://www.raspberrypi.org/downloads/raspbian/
The headless variant as of writing this is Buster Lite. After downloading we need to flash the image onto a microSD card for the raspberry. The easiest way to do this is with balenaEtcher which can be downloaded here:
Etcher automatically unmounts the card so after flashing the image remove then replace the microSD card. To enable SSH you need to create a file entitled SSH on the root partition of the SD named ‘boot’. On mac or Linux you can do this in the command line by navigating to the boot partition and then using command ‘touch ssh’ which will create a file of that name if it does not already exist:
touch ssh
If you are connecting to the pi via Ethernet cable you can skip this next step.
To connect via wifi you need to create another file in the boot partition named:
wpa_supplicant.conf
With contents:
country=US
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid="your_real_wifi_ssid"
scan_ssid=1
psk="your_real_password"
key_mgmt=WPA-PSK
}
Change the country code, ssid and psk (pre-shared key) to your own. The password is only stored here in plain text upon first boot, the Pi will move this file automatically.