Summary

Blinkt! is an LED light strip attachable to the GPIO extension on Raspberry Pi’s. Sealsystems provides a rainbow container that creates a rainbow of the LEDs and can be orchestrated on a Docker cluster using the Swarm orchestrator. This is a description of how to run the rainbow on a Kubernetes cluster.

Prerequisites

• Raspberry Pi’s with Pimoroni Blinkt!
• Kubernetes cluster (Hypriot for Raspberry Pi)
• Sealsystems Rainbow Container (sealsystems/rainbow:latest)

Description

The Rainbow container uses the node package (npm), node-blinkt, to interact with the LEDs through the host GPIO. To access the GPIO, the container will need access to the host’s /sys directory which acts as a virtual filesystem for the system devices (/sys/devices/gpiochip2/gpio/). Mount the host’s /sys directory to the container and the Blinkt! package will be able to access the GPIO.

        containers:
             - name: rainbow
               image: sealsystems/rainbow:latest
               volumeMounts:
                       - name: sys
                         mountPath: /sys
        volumes:
             - name: sys
               hostPath: 
                   path: /sys

There is only one GPIO and Blinkt! light per host so running the rainbow container as a DaemonSet will ensure that only one (1) container is run on each host in the cluster.

apiVersion: apps/v1
kind: DaemonSet
metadata:
    name: rainbow

By default the master node will be excluded from cluster nodes in the DaemonSet so in a 5-node cluster, only the (four) 4 worker nodes will light up.

Use tolerations to enable the DaemonSet to to run on the master node.

spec:
# this toleration is to have a daemonset run or not run on the master node
# key - node key to identify master node
# effect - specifies whether to run (NoSchedule) or not run (NoExecute)
    tolerations:
         - key: node-role.kubernetes.io/master
           effect: NoSchedule

Steps

Create yaml file, rainbow.yml

apiVersion: apps/v1
kind: DaemonSet
metadata:
    name: rainbow
spec:
    selector:
        matchLabels:
            name: rainbow
    template:
        metadata:
            labels:
                name: rainbow
        spec:
            tolerations:
                 - key: node-role.kubernetes.io/master
                   effect: NoSchedule
            containers:
                 - name: rainbow
                   image: sealsystems/rainbow:latest
                   volumeMounts:
                           - name: sys
                             mountPath: /sys
            volumes:
                 - name: sys
                   hostPath: 
                       path: /sys

Apply to cluster:
kubectl apply -f rainbow.yml