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Kubernetes and LinuxKit

CircleCI

This project aims to demonstrate how one can create minimal and immutable Kubernetes OS images with LinuxKit.

Build requirements

To build images and to rebuild the individual packages you will need the LinuxKit tool

If you already have go installed you can use go get -u github.com/linuxkit/linuxkit/src/cmd/linuxkit to install the tool.

On MacOS there is a brew tap available. Detailed instructions are at linuxkit/homebrew-linuxkit, the short summary is

brew tap linuxkit/linuxkit
brew install --HEAD linuxkit

Build requirements from source:

  • GNU make
  • Docker
  • optionally qemu

Building OS images

To build the default OS images:

make all

By default this will build images using Docker Engine for execution. To instead use cri-containerd use:

make all KUBE_RUNTIME=cri-containerd

Booting and initialising OS images

Boot Kubernetes master OS image using hyperkit on macOS: or qemu on Linux:

./boot.sh

or, to automatically initialise the cluster upon boot with no additional options

KUBE_MASTER_AUTOINIT="" ./boot.sh

Get IP address of the master:

ip addr show dev eth0

Login to the kubelet container:

./ssh_into_kubelet.sh <master-ip>

Manually initialise master with kubeadm if booted without KUBE_MASTER_AUTOINIT:

kubeadm-init.sh

Once kubeadm exits, make sure to copy the kubeadm join arguments, and try kubectl get nodes from within the master.

If you just want to run a single node cluster with jobs running on the master, you can use:

kubectl taint nodes --all node-role.kubernetes.io/master- --kubeconfig /etc/kubernetes/admin.conf

To boot a node use:

./boot.sh <n> [<join_args> ...]

More specifically, to start 3 nodes use 3 separate shells and run this:

shell1> ./boot.sh 1 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443 --discovery-token-unsafe-skip-ca-verification
shell2> ./boot.sh 2 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443 --discovery-token-unsafe-skip-ca-verification
shell3> ./boot.sh 3 --token bb38c6.117e66eabbbce07d 192.168.65.22:6443 --discovery-token-unsafe-skip-ca-verification

Platform specific information

MacOS

The above instructions should work as is.

Linux

By default linuxkit run uses user mode networking which does not support access from the host. To workaround this you can use port forwarding e.g.

KUBE_RUN_ARGS="-publish 2222:22" ./boot.sh

ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -p 2222 root@localhost

However you will not be able to run worker nodes since individual instances cannot see each other.

To enable networking between instance unfortunately requires root privileges to configure a bridge and setup the bridge mode privileged helper.

See http://wiki.qemu.org/Features/HelperNetworking for details in brief you will need:

  • To setup and configure a bridge (including e.g. DHCP etc) on the host. (You can reuse a bridge created by e.g. virt-mananger)

  • To set the qemu-bridge-helper setuid root. The location differs by distro, it could be /usr/lib/qemu/qemu-bridge-helper or /usr/local/libexec/qemu-bridge-helper or elsewhere. You need to chmod u+s «PATH».

  • List the bridge created in the first step in /etc/qemu/bridge.conf with a line like allow br0 (if your bridge is called br0).

  • Set KUBE_NETWORKING=bridge,«name» e.g.

    KUBE_NETWORKING="bridge,br0" ./boot.sh KUBE_NETWORKING="bridge,br0" ./boot.sh 1 «options»

Configuration

The boot.sh script has various configuration variables at the top which can be overridden via the environment e.g.

KUBE_VCPUS=4 ./boot.sh