led

Controlling a LED through KubeEdge

This example walks through how to control a LED hooked to a Raspberry Pi, via a Kubernetes pod deployed through KubeEdge.

Pre-requisites

Kubernetes Cluster

The example assumes that there is a Kubernetes cluster already created, accessible through kubectl. If you don't have one, you can use Kind to create one locally.

KubeEdge

The example assumes that KubeEdge has already been installed in the cluster, exposing the cloudcore component so that it's accessible from an edge device.

Edge Device

The example assumes that the edge device is a Raspberry Pi with an ARMv7 architecture of 32 bits. In particular, the example has been tested with a Raspberry Pi 3 Model B V1.2. We will assume that this device has been pre-synced through KubeEdge and that it's already visible as a node in the cluster with name raspberry.

The example also requires that the Raspberry Pi has a LED attached as the diagram shown above.

LED Blinker

We will leverage the gpiozero library to implement a quick script which makes the attached LED blink. Then, we will containerise it and deploy it to our raspberry node leveraging KubeEdge.

Implementation

The code itself is very simple. It will make the led blink every second.

%%writefile led.py
from gpiozero import LED
from time import sleep

led = LED(17)

while True:
    led.on()
    sleep(1)
    led.off()
    sleep(1)

Containerisation

The next step will be containerising this example as a Docker image which can be deployed later. Note that this image needs to be compatible with the ARM architecture of the Raspberry Pi.

For that, we will leverage the arm32v7/python image as base.

%%writefile Dockerfile
FROM arm32v7/python:3.7.8-slim

WORKDIR /usr/src/app

COPY requirements.txt ./
RUN pip install -r requirements.txt

COPY . .

CMD [ "python", "./led.py" ]

!docker build \
    . \
    --platform linux/arm/v7 \
    -t adriangonz/kubeedge-led-example:0.1.0-arm
!docker push adriangonz/kubeedge-led-example:0.1.0-arm

Deployment

The last step is to create a Pod which runs our led.py script.

It's worth noting that this pod needs privileged access to the /dev/gpiomem file, which maps the GPIO board in the Raspberry Pi. We can achieve this by leveraging Kubernetes volumes support.

%%writefile ./charts/pod-led-example.yaml
apiVersion: v1
kind: Pod
metadata:
  name: led-example
  namespace: examples
spec:
  containers:
    - name: led-example
      image: adriangonz/kubeedge-led-example:0.1.0-arm
      volumeMounts:
        - mountPath: /dev/gpiomem
          name: dev-gpiomem
      securityContext:
        privileged: true
  volumes:
    - name: dev-gpiomem
      hostPath:
        path: /dev/gpiomem
  nodeName: raspberry

Note that the Pod definition is standard Kubernetes. Once we've got it, we can simply deploy it using kubectl as any regular resource.

!kubectl apply -f ./charts/pod-led-example.yaml