Ansible 2 Playbooks for installing Kubernetes on Raspberry Pis 3

Here are the Ansible playbooks for a Raspberry Pi Cluster running Docker and Kubernetes as described in this Blog Post. These playbooks require Ansible 2.0 and won't work with Ansible 1.x.

The goals of thise project are

• Using Ansible for not only a one-shot installation but also maintainance and upgrades.
• Using WiFi for connecting the cluster. See below for the reason.
• Get OpenShift Origin running and be able to switch between Kubernetes and OpenShift via Ansible.
• Create a demonstration platform for my favourite development and integration platform fabric8.

Shopping List

Here's a shopping list for a Raspberry Pi 3 cluster, along with (non-affiliate) links to (German) shops (as of April 2016), but I'm sure you can find them elswhere, too.

Amount	Part	Price
4	Raspberry Pi 3	4 * 38 EUR
4	Micro SD Card 32 GB	4 * 11 EUR
1	WLAN Router	22 EUR
4	USB wires	9 EUR
1	Power Supply	30 EUR
1	Case	10 EUR
3	Intermediate Case Plate	3 * 7 EUR

All in all, a 4 node Pi cluster for 288 EUR (as of April 2016).

Some remarks:

• Using WiFi for the connection has the big advantage that the Raspberry Pi 3 integrated BCM43438 WiFi chip doesn't go over USB and saves valuable bandwidth used for IO in general. That way you are able to to get ~ 25 MB/s for disk IO and network traffic, respectively. And also less cables, of course. You can alway plug the power wire for demos, too ;-)
• Use a class 10 Mirco SD but it doesn't have to be the fastest on the world at the USB bus only allows around 25 MB/s anyway.

Initial Pi Setup

Most of the installation is automated by using Ansible. Thanks to Hypriot images a complete headless setup is possible.

1. Download the latest Hyoriot image and store it as hypriot.zip :

    curl -L https://github.com/hypriot/image-builder-rpi/releases/download/v1.7.1/hypriotos-rpi-v1.7.1.img.zip -o hypriot.zip
   

2. Install Hypriot's flash installer script. Follow the directions on the installation page. Important: For using the latest Hypriot Images >= 1.7.0 please use the Shell script from the master branch. The latest release 0.2.0 does not yet support the new configuration used by Hypriot 1.7.0. The script must be reachable from within your $PATH and it must be executable.

3. Insert you Micro-SD card in your Desktop computer (via an adapter possibly) and run the wrapper script

tools/flash-hypriot.sh --hostname n0 --ssid "mysid" --password "secret" --image hypriot.zip

"mysid" is your WLAN SID and "secret" the corresponding password. You will be asked to which device to write. Check this carefully, otherwise you could destroy your Desktop OS if selecting the the wrong device. Typically its something like /dev/disk2 on OS X, but depends on the number of hard drives you have.

4. Repeat step 2. to 3. for each Micro SD card. Please adapt the hostname before each round to n1, n2, n3.

Network Setup

It is now time to configure your WLAN router. This of course depends on which router you use. The following instructions are based on a TP-Link TL-WR802N which is quite inexepensive but still absolutely ok for our purposes since it sits very close to the cluster and my notebook anyway.

First of all you need to setup the SSID and password. Use the same credentials with which you have configured your images.

My setup is, that I span a private network 192.168.23.0/24 for the Pi cluster which my MacBook also joins via its integrated WiFi.

The addresses I have chosen are :

IP	Device
192.168.23.1	WLAN Router
192.168.23.100	MacBook's WLAN
192.168.23.200 ... 192.168.23.203	Raspberry Pis

The MacBook is setup for NAT and forwarding from this private network to the internet. This script helps in setting up the forwarding and NAT rules on OS X.

In order to configure your WLAN router you need to connect to it according to its setup instructions. The router is setup in Access Point mode with DHCP enabled. As soon as the MAC of the Pis are known (which you can see as soon as they connect for the first time via WiFi), I configured them to always use the same DHCP lease. For the TL-WR802N this can be done in the configuration section DHCP -> Address Reservation. In the DHCP -> DHCP-Settings the default gateway is set to 192.168.23.100, which my notebook's WLAN IP.

Startup all nodes, you should be able to ping every node in your cluster. I added n0 ... n3 to my notebook's /etc/hosts pointing to 192.168.23.200 ... 192.168.23.203 for convenience.

You should be able to ssh into every Pi with user pirate and password hypriot. Also, if you set up the forwarding on your desktop properly you should be able to ping from within the pi to the outside world. Internet access from the nodes is mandatory for setting up the nodes with Ansible

Ansible Playbooks

After this initial setup is done, the next step is to initialize the base system with Ansible. You will need Ansible 2 installed on your desktop (e.g. brew install ansible when running on OS X)

Ansible Configuration

1. Checkout the Ansible playbooks:

    git clone https://github.com/Project31/ansible-kubernetes-openshift-pi3.git k8s-pi
    cd k8s-pi
   

2. Copy over hosts.example and adapt it to your needs

    cp hosts.example hosts
    vi hosts
   

   There are three groups:

   • pis contains all members of your cluster where one is marked as "master" in the field host_extra. This group will be added to every node in its /etc/hosts. It is important that one host is marked as "master", since the playbooks rely on this host alias for accessing the API server.
   • master IP address of the Master
   • nodes All nodes which are not Master

3. If required, copy over the configuration and adapt it:

    cp config.yml.example config.yml
    vi config.yml
   

Init machine-id

Because of a pecularity of Hypriot OS 1.5 which causes every machine id to be the same, /etc/machine-id need to be initialized once for each node. This is required later e.g. by the Weave overlay network as it calculates its virtual Mac address from this datum.

To do so, call the following Ansible ad-hoc command:

ansible pis -u pirate -k -i hosts --become -m shell --args "dbus-uuidgen > /etc/machine-id"

Use "hypriot" as password here. You can also use the script tools/init_machine_id.sh. If you get errors during this command, please check that you don't have stale entries

Basic Node Setup

If you have already created a cluster with these playbooks and want to start a fresh, please be sure that you cleanup your ~/.ssh/known_hosts from the old host keys. The script tools/cleanup_known_hosts.sh can be used for this. You should be able to ssh into each of the nodes without warnings. Also you must be able to reach the internet from the nodes.

In the next step the basic setup (without Kubernetes) is performed. This is done by

ansible-playbook -k -i hosts setup.yml

When you are prompted for the password, use hypriot. You will probably also need to confirm the SSH authentity for each host with yes.

The following steps will be applied by this command (which may take a bit):

• Docker will be installed from the Hypriot repositories
• Your public SSH key .ssh/id_rsa.pub is copied over to pi's authenticated_keys and the users password will be taken from config.yml
• Some extra tools are installed for your convenience and some benchmarking:
  • hdparm
  • iperf
  • mtr
  • vim
  • dnsutils
  • jq
• Hostname is set to the name of the node configured. Also /etc/hosts is setup to contain all nodes with their short names.

With this basic setup you have already a working Docker environment.

Ingress

As ingress controller we use traefik. It will get deployed as part of management playbook and will run as DaemonSet.

To test ingress add <nodeIPAddress> traefik-ui.pi.local dashboard.pi.local to your /etc/hosts file.

For any other resource you want to export - create ingress resource:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: traefik-web-ui
  namespace: kube-system
  labels:
    k8s-app: traefik-ingress-lb
spec:
  rules:
  - host: traefik-ui.pi.local
    http:
      paths:
      - path: /
        backend:
          serviceName: traefik-service
          servicePort: admin

Kubernetes Setup

The final step for a working Kubernetes cluster is to run

ansible-playbook -i hosts kubernetes.yml

This will install one master at n0 and threed additional nodes n1, n2, n3 with the help of kubeadm

In addition this playbook does the following:

• Creates a token in run/kubeadm-token.txt if not done already and use it for installing master and nodes
• Installs kubectl and an alias k
• Creates a run/pi-cluster.cfg which can be used for kubectl on the local host to access the pi cluster's master. Either use kubectl --kubeconfig run/pi-cluster.cfg or set the environment variable export KUBECONFIG=$(pwd)/run/pi-cluster.cfg

The initial installation may take a bit until all infrastructure docker images has been pulled from the registry. Eventually you should be able to use kubectl get nodes from e.g. n0 or from the localhost (if you set the config as described above).

Full Kubernetes reset

In case you need a full cleanup of the Kubernetes setup, use:

ansible-playbook -i hosts kubernetes-full-reset.yml

This is also needed in case you want to change one of the Pod or Services subnets.

Tools

In the tools/ directory you find some useful scripts:

• cleanup_known_hosts.sh for removing the entries for n0, n1, n2 and n3 in ~/.ssh/known_hosts in case you want to completely reinstall the cluster
• setup_nat_on_osx.sh switches on NAT so that the cluster can reach the Internet for loading the required images. Call it without arguments for usage informations
• setup_nat_off_osx.sh switches off NAT again.
• halt_pis.sh stop the cluster (needs still a bit of tuning)
• reboot_pis.sh reboot the cluster (needs still a bit of tuning)
• init_machine_id.sh initialize the /etc/machine-id to a random value on every host

FAQ

• I have random DNS issues when resolving external IP adresses

One reason for this could be, that your external DNS provider does some nasty things when a resolution fails (which then might be even cached by Kubernetes). E.g. the Deutsche Telekom is known that by default it enables a so called "Navigationshilfe" which redirect for a failed DNS lookup to their own pages. You can turn this off in the "Kundencenter" preferences. More on the symptoms can be found in this issue

Next steps ...

For the future we plan the following features to add:

• Volume support
• Registry
• OpenShift support

Acknowledgements

• Many thanks goes out to Lucas Käldström whose kubeadm workshop gave a lot of inspiration to these playbooks.
• Thanks to Sergio Sisternes for the inspiration to switch to kubeadm which makes things much easier and the manual setup of etcd and flanneld superfluous.
• Many kudos to Robert Peteuil for a thorough review of the Ansible tasks and update information for Hypriot 1.5. This has simplified the role definitions considerably.
• Thanks to Mangirdas Judeikis for updating the playbooks to Kubernetes 1.9, Ansible 2.4 and introducing Traefik as load balancer.