aaronkjones / rpi-k8s-node-prep

Prepares a Raspberry Pi node for Kubernetes

This was adapted from a gist by alexellis

Kubernetes on Raspbian/Hypriot

Hypriot make a Docker image for Raspberry Pi that is a good starting point for running Kubernetes on the Pi. Alternatively, using vanilla Raspbian is a safe bet as well.

Pre-reqs:

• 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)

Automatic preparation

To prepare a node with the script, on each node run the following command:

The safe way...

wget https://raw.githubusercontent.com/aaronkjones/rpi-k8s-node-prep/master/prep.sh
chmod +x prep.sh
./prep.sh

or, with single command...

curl -sL https://raw.githubusercontent.com/aaronkjones/rpi-k8s-node-prep/master/prep.sh | sudo bash

This script:

• Installs Docker
• Adds user to Docker group (pi or pirate depending if using Raspbian or Hypriot OS)
• Allows you to install a different version of Docker
• Disables Swap
• Installs latest Kubernetes or specific version
• Allows you to pin specific version of Docker and Kubernetes to prevent it being upgraded when apt-get upgrade is run
• Backs up cmdline.txt
• Adds cgroup options to cmdline.txt
• If the node is a "master" it removes KUBELET_NETWORK_ARGS from /etc/systemd/system/kubelet.service.d/10-kubeadm.conf

After running the script continue this guide from setup networking

Manual node setup

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 cluste breaks because the IP of your master changed. 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 for each node in your cluster as you see fit.

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 the latest version of Docker. Using the script above, you can set a specific version of Docker.

$ curl -sSL get.docker.com | sh && \
sudo usermod pi -aG docker

Disable swap

For Kubernetes 1.7 and newer 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=1.10.2-00 kubectl=1.10.2-00 kubelet=1.10.2-00

To install a later version, remove the version flag at the end (e.g. 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

Modify 10-kubeadm.conf on the master node only

$ sudo sed -i '/KUBELET_NETWORK_ARGS=/d' /etc/systemd/system/kubelet.service.d/10-kubeadm.conf

Initialize your master node:

$ 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=192.168.0.27 with the IP of the Pi.

Note: This step will take a long time, even up to 15 minutes.

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.

Setup networking

Install Flannel network driver

$ curl -sSL https://rawgit.com/coreos/flannel/v0.9.1/Documentation/kube-flannel.yml | sed "s/amd64/arm/g" | kubectl create -f -

Join other nodes

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

Copy and paste the command provided after Kubeadm init completes. It should look something like this:

$ sudo kubeadm join <master ip>:6443 --token <token> --discovery-token-ca-cert-hash sha256:1c06faa186e7f85...

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

Deploy a container

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: TCP

Deploy 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.

Start up the dashboard

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.

Remove the test deployment

Now on the Kubernetes master remove the test deployment:

$ kubectl delete -f function.yml