Yes - you can create a Kubernetes cluster with Raspberry Pis with the default operating system called Raspbian. This means you can carry on using all the tools and packages you're used to with the officially-supported OS.
This is part of a blog post Serverless Kubernetes home-lab with your Raspberry Pis written by Alex Ellis.
Copyright disclaimer: Please provide a link to the post and give attribution to the author if you plan to use this content in your own materials.
- You must use an RPi 2 or 3 for use with Kubernetes
- I'm assuming you're using wired ethernet (Wi-Fi also works, but it's not recommended)
You can either follow the steps below, or use my flashing script which automates the below. The automated flashing script must be run on a Linux computer with an SD card writer or an RPi.
Provision a Raspberry Pi SD card
Then run:
curl -sLSf https://gist.githubusercontent.com/alexellis/fdbc90de7691a1b9edb545c17da2d975/raw/125ad6eae27e40a235412c2b623285a089a08721/prep.sh | sudo sh
- Flash Raspbian to a fresh SD card.
You can use Etcher.io to burn the SD card.
Before booting set up an empty file called ssh in /boot/ on the SD card.
Use Raspbian Stretch Lite
Update: I previously recommended downloading Raspbian Jessie instead of Stretch. At time of writing (3 Jan 2018) Stretch is now fully compatible.
https://www.raspberrypi.org/downloads/raspbian/
- Change hostname
Use the raspi-config utility to change the hostname to k8s-master-1 or similar and then reboot.
- Set a static IP address
It's not fun when your cluster breaks because the IP of your master changed. The master's certificates will be bound to the IP address, so let's fix that problem ahead of time:
cat >> /etc/dhcpcd.conf
Paste this block:
profile static_eth0
static ip_address=192.168.0.100/24
static routers=192.168.0.1
static domain_name_servers=8.8.8.8
Hit Control + D.
Change 100 for 101, 102, 103 etc.
You may also need to make a reservation on your router's DHCP table so these addresses don't get given out to other devices on your network.
- Install Docker
This installs 17.12 or newer.
$ curl -sSL get.docker.com | sh && \
sudo usermod pi -aG docker
newgrp docker
- Disable swap
For Kubernetes 1.7 and onwards you will get an error if swap space is enabled.
Turn off swap:
$ sudo dphys-swapfile swapoff && \
sudo dphys-swapfile uninstall && \
sudo update-rc.d dphys-swapfile remove
This should now show no entries:
$ sudo swapon --summary
- Edit
/boot/cmdline.txt
Add this text at the end of the line, but don't create any new lines:
cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory
Now reboot - do not skip this step.
- Add repo lists & install
kubeadm
$ curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add - && \
echo "deb http://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee /etc/apt/sources.list.d/kubernetes.list && \
sudo apt-get update -q && \
sudo apt-get install -qy kubeadm
I realise this says 'xenial' in the apt listing, don't worry. It still works.
- You now have two new commands installed:
- kubeadm - used to create new clusters or join an existing one
- kubectl - the CLI administration tool for Kubernetes
If using Weave Net
- Initialize your master node:
$ sudo kubeadm init --token-ttl=0
If using Flannel:
- Initialize your master node with a Pod network CIDR:
$ sudo kubeadm init --token-ttl=0 --pod-network-cidr=10.244.0.0/16
We pass in --token-ttl=0 so that the token never expires - do not use this setting in production. The UX for kubeadm means it's currently very hard to get a join token later on after the initial token has expired.
Optionally also pass
--apiserver-advertise-address=192.168.0.27with the IP of the Pi as found by typingifconfig.
Note: This step can take a long time, even up to 15 minutes.
Sometimes this stage can fail, if it does then you should patch the API Server to allow for a higher failure threshold during initialization around the time you see [controlplane] wrote Static Pod manifest for component kube-apiserver to "/etc/kubernetes/manifests/kube-apiserver.yaml"
sudo sed -i 's/failureThreshold: 8/failureThreshold: 20/g' /etc/kubernetes/manifests/kube-apiserver.yaml
After the init is complete run the snippet given to you on the command-line:
mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config
This step takes the key generated for cluster administration and makes it available in a default location for use with kubectl.
- Now save your join-token
Your join token is valid for 24 hours, so save it into a text file. Here's an example of mine:
$ kubeadm join --token 9e700f.7dc97f5e3a45c9e5 192.168.0.27:6443 --discovery-token-ca-cert-hash sha256:95cbb9ee5536aa61ec0239d6edd8598af68758308d0a0425848ae1af28859bea
- Check everything worked:
$ kubectl get pods --namespace=kube-system
NAME READY STATUS RESTARTS AGE
etcd-of-2 1/1 Running 0 12m
kube-apiserver-of-2 1/1 Running 2 12m
kube-controller-manager-of-2 1/1 Running 1 11m
kube-dns-66ffd5c588-d8292 3/3 Running 0 11m
kube-proxy-xcj5h 1/1 Running 0 11m
kube-scheduler-of-2 1/1 Running 0 11m
weave-net-zz9rz 2/2 Running 0 5m
You should see the "READY" count showing as 1/1 for all services as above. DNS uses three pods, so you'll see 3/3 for that.
Some users have reported stability issues with Weave Net on ARMHF. These issues do not appear to affect x86_64 (regular PCs/VMs). You may want to try Flannel instead of Weave Net for your RPi cluster.
Install Weave Net network driver
$ kubectl apply -f \
"https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"
If you run into any issues with Weaveworks' networking then flannel is also a popular choice for the ARM platform.
Apply the Flannel driver on the master:
$ kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/c5d10c8/Documentation/kube-flannel.yml
On each node that joins including the master:
$ sudo sysctl net.bridge.bridge-nf-call-iptables=1
On the other RPis, repeat everything apart from kubeadm init.
- Change hostname
Use the raspi-config utility to change the hostname to k8s-worker-1 or similar and then reboot.
- Join the cluster
Replace the token / IP for the output you got from the master node, for example:
$ sudo kubeadm join --token 1fd0d8.67e7083ed7ec08f3 192.168.0.27:6443
You can now run this on the master:
$ kubectl get nodes
NAME STATUS AGE VERSION
k8s-1 Ready 5m v1.7.4
k8s-2 Ready 10m v1.7.4
This container will expose a HTTP port and convert Markdown to HTML. Just post a body to it via curl - follow the instructions below.
function.yml
apiVersion: v1
kind: Service
metadata:
name: markdownrender
labels:
app: markdownrender
spec:
type: NodePort
ports:
- port: 8080
protocol: TCP
targetPort: 8080
nodePort: 31118
selector:
app: markdownrender
---
apiVersion: apps/v1beta1 # for versions before 1.6.0 use extensions/v1beta1
kind: Deployment
metadata:
name: markdownrender
spec:
replicas: 1
template:
metadata:
labels:
app: markdownrender
spec:
containers:
- name: markdownrender
image: functions/markdownrender:latest-armhf
imagePullPolicy: Always
ports:
- containerPort: 8080
protocol: TCPDeploy and test:
$ kubectl create -f function.yml
Once the Docker image has been pulled from the hub and the Pod is running you can access it via curl:
$ curl -4 http://127.0.0.1:31118 -d "# test"
<p><h1>test</h1></p>
If you want to call the service from a remote machine such as your laptop then use the IP address of your Kubernetes master node and try the same again.
The dashboard can be useful for visualising the state and health of your system, but it does require the equivalent of "root" in the cluster. If you want to proceed you should first run in a ClusterRole from the docs.
echo -n 'apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
name: kubernetes-dashboard
labels:
k8s-app: kubernetes-dashboard
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: cluster-admin
subjects:
- kind: ServiceAccount
name: kubernetes-dashboard
namespace: kube-system' | kubectl apply -f -
This is the development/alternative dashboard which has TLS disabled and is easier to use.
$ kubectl apply -f https://raw.githubusercontent.com/kubernetes/dashboard/master/src/deploy/alternative/kubernetes-dashboard-arm.yaml
You can then find the IP and port via kubectl get svc -n kube-system. To access this from your laptop you will need to use kubectl proxy and navigate to http://localhost:8001/ on the master, or tunnel to this address with ssh.
See also: Kubernetes Dashboard docs.
Now on the Kubernetes master remove the test deployment:
$ kubectl delete -f function.yml
You should now have an operational Kubernetes master and several worker nodes ready to accept workloads.
Now let's head back over to the tutorial and deploy OpenFaaS to put the cluster through its paces with Serverless functions.
See also: Kubernetes documentation