High Availability Cluster

You can perform Kubernetes high availability cluster installation. You can configure multi-master node configuration using HAProxy and Keepalived and provide continuous accessibility with virtual IP address.

1) HAProxy Installation

HAProxy is an open-source proxy and load balancing solution used to provide load balancing and high availability. Installation on Ubuntu operating systems is described below.

sudo apt update

HAProxy installation is performed.

sudo apt install haproxy

Configuration file is edited.

sudo vi /etc/haproxy/haproxy.cfg

You can add the following commands to the bottom of the file. Edit the hostname and IP fields according to yourself.

frontend kubernetes-frontend
  bind *:6443
  mode tcp
  option tcplog
  default_backend kubernetes-backend

backend kubernetes-backend
  option httpchk GET /healthz
  http-check expect status 200
  mode tcp
  option ssl-hello-chk
  balance roundrobin
  server <master1hostname> <MASTER_1_IP>:6443 check fall 3 rise 2
  server <master2hostname> <MASTER_2_IP>:6443 check fall 3 rise 2
  server <master3hostname> <MASTER_3_IP>:6443 check fall 3 rise 2

systemctl enable haproxy && systemctl restart haproxy
systemctl status haproxy

2) Keepalived Installation

Keepalived provides a virtual IP address between multiple control nodes (master and backup masters) and is used to ensure continuous operation of other services.

sudo apt install keepalived

sudo vim /etc/keepalived/check_apiserver.sh

The following script performs availability check to the Kubernetes API server. Replace the <VIRTUAL_IP> part with the virtual ip you will add in the next step.

#!/bin/sh

errorExit() {
  echo "*** $@" 1>&2
  exit 1
}

curl --silent --max-time 2 --insecure https://localhost:6443/ -o /dev/null || errorExit "Error GET https://localhost:6443/"
if ip addr | grep -q <VIRTUAL_IP>; then
  curl --silent --max-time 2 --insecure https://<VIRTUAL_IP>:6443/ -o /dev/null || errorExit "Error GET https://<VIRTUAL_IP>:6443/"
fi

chmod +x /etc/keepalived/check_apiserver.sh

sudo vim /etc/keepalived/keepalived.conf

If the keepalived.conf file is not empty, you can clear its content and add the following command lines.

Important: Add the appropriate network unit opposite the interface. Replace the <VIRTUAL_IP> part with the IP address you want to add.

vrrp_script check_apiserver {
  script "/etc/keepalived/check_apiserver.sh"
  interval 3
  timeout 10
  fall 5
  rise 2
  weight -2
}

vrrp_instance VI_1 {
    state BACKUP
    interface eth1
    virtual_router_id 1
    priority 100
    advert_int 5
    authentication {
        auth_type PASS
        auth_pass mysecret
    }
    virtual_ipaddress {   
     <VIRTUAL_IP>    
 }
    track_script {
        check_apiserver
    }
}

systemctl enable --now keepalived

Starting Kubernetes Cluster

You can perform Kubernetes installation from the Kubernetes Installation on Ubuntu Operating System document.

Important: When performing the init operation, you must enter your own virtual IP address to the endpoint as follows.

kubeadm init --control-plane-endpoint="<VIRTUAL_IP>:6443" --upload-certs --pod-network-cidr=10.244.0.0/16