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====== Keepalived ======

ha high availability redundancy failover

Aplicacion para proveer de Alta Disponibilidad a dos servidores, que compartiran una direccion IP. Uno sera el activo y los demás pasivos.

Fuente: https://github.com/kubernetes/kubeadm/blob/master/docs/ha-considerations.md#keepalived-configuration

===== Requisitos =====

  * Dos o más servidores que tengan una IP en la misma subred. Funciona con IPs públicas.

===== Instalacion =====

  sudo apt-get update && sudo apt-get install -y keepalived

===== Configuración =====

En este ejemplo la IP flotante será '8.8.8.8'.

1. Crear archivo:

  sudo vim /etc/keepalived/keepalived.conf

Con el siguiente contenido:

<code>
! /etc/keepalived/keepalived.conf
! Configuration File for keepalived
global_defs {
    router_id LVS_DEVEL
}
vrrp_script check_apiserver {
  script "/etc/keepalived/check_apiserver.sh"
  interval 3
  weight -2
  fall 10
  rise 2
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 101
    authentication {
        auth_type PASS
        auth_pass k8s
    }
    virtual_ipaddress {
        45.150.187.221
    }
    track_script {
        check_apiserver
    }
}
</code>

Comentarios:

  * State. Is MASTER for one and BACKUP for all other hosts, hence the virtual IP will initially be assigned to the MASTER.
  * Interface. Is the network interface taking part in the negotiation of the virtual IP, e.g. eth0.
  * Virtual_router_id. Should be the same for all keepalived cluster hosts while unique amongst all clusters in the same subnet. Many distros pre-configure its value to 51.
  * Priority. Should be higher on the control plane node than on the backups. Hence 101 and 100 respectively will suffice.
  * Auth_pass. Should be the same for all keepalived cluster hosts, e.g. 42
  * Virtual_ipaddress. Is the virtual IP address negotiated between the keepalived cluster hosts.

2. Crear archivo:

  sudo vim /etc/keepalived/check_apiserver.sh

Con el siguiente contenido:

<code>
#!/bin/sh

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

curl --silent --max-time 2 --insecure http://localhost/ -o /dev/null || errorExit "Error GET https://localhost/"
if ip addr | grep -q 8.8.8.8; then
    curl --silent --max-time 2 --insecure http://8.8.8.8/ -o /dev/null || errorExit "Error GET http://8.8.8.8/"
fi
</code>

Reemplazar '8.8.8.8' por la IP flotante a usar.

3. Dar permisos de ejecución:

  sudo chmod +x /etc/keepalived/check_apiserver.sh

4. Habilitar el servicio keepalived:

  sudo systemctl enable keepalived --now

5. Repetir los pasos 1 a 4 para el resto de nodos, ajustando los valores según los comentarios de cada paso

6. Probar:

6.1. Ejecutar:

  wget http://8.8.8.8
  
Reemplazar '8.8.8.8' por la IP flotante a usar.  

6.2. Apagar el nodo que tenga la IP flotante en ese momento

6.3. Repetir el paso 6.1.