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Multi-master cluster

This example shows how to use Kubitect to set up a Kubernetes cluster with 3 master and 3 worker nodes. Configuring multiple master nodes provides control plane redundancy, meaning that the control plane can continue to operate normally if a certain number of master nodes fail. Since Kubitect deploys clusters with a stacked control plane (see Kubernetes.io - Stacked etcd topology for more information), this means that there is no downtime as long as (n/2)+1 master nodes are available.

Architecture of the cluster with 3 master and 3 worker nodes

Note

In this example we skip the explanation of some common configurations (hosts, network, node template, ...), as they are already explained in the Getting started (step-by-step) guide.

Step 1: Cluster configuration🔗︎

Each worker node stores only a single control plane IP address. Therefore, when creating clusters with multiple master nodes, we need to make sure that all of them are reachable at the same IP address, otherwise all workers would send requests to only one of the master nodes. This problem can be solved by placing a load balancer in front of the control plane, and instructing it to distribute traffic to all master nodes in the cluster, as shown in the figure below.

Scheme of load balancing between control plane nodes

To create such cluster, all we need to do, is specify desired node instances and one load balancer. Control plane will be accessible on the load balancer's IP address.

multi-master.yaml
cluster:
  ...
  nodes:
    loadBalancer:
      instances:
        - id: 1
          ip: 192.168.113.100
    master:
      instances: # (1)!
        - id: 1
          ip: 192.168.113.10
        - id: 2
          ip: 192.168.113.11
        - id: 3
          ip: 192.168.113.12
    worker:
      instances:
        - id: 1
          ip: 192.168.113.20
        - id: 2
          ip: 192.168.113.21
        - id: 3
          ip: 192.168.113.22
  1. Size of the control plane (number of master nodes) must be odd.

Kubitect detects the load balancer instance in the configuration and installs the HAProxy load balancer on an additional virtual machine. By default, the load balancer is configured to distribute traffic received on port 6443 (Kubernetes API server port) to all specified master nodes.

Final cluster configuration
multi-master.yaml
hosts:
  - name: localhost
    connection:
      type: local

cluster:
  name: local-k8s-cluster
  network:
    mode: nat
    cidr: 192.168.113.0/24
  nodeTemplate:
    user: k8s
    updateOnBoot: true
    ssh:
      addToKnownHosts: true
    os:
      distro: ubuntu
  nodes:
    loadBalancer:
      instances:
        - id: 1
          ip: 192.168.113.100
    master:
      instances:
        - id: 1
          ip: 192.168.113.10
        - id: 2
          ip: 192.168.113.11
        - id: 3
          ip: 192.168.113.12
    worker:
      instances:
        - id: 1
          ip: 192.168.113.20
        - id: 2
          ip: 192.168.113.21
        - id: 3
          ip: 192.168.113.22

kubernetes:
  version: v1.23.7
  networkPlugin: calico
  dnsMode: coredns
  kubespray:
    version: v2.19.0

Step 2: Applying the configuration🔗︎

Apply the cluster: 

kubitect apply --config multi-master.yaml