High Availability with keepalived

Saturday. April 10, 2021 - 3 mins

INTRODUCTION

keepalived can be used to monitor services or systems and to automatically failover to a standby node if problems occur. High availability is achieved by the Virtual Redundancy Routing Protocol (VRRP). As a result, high availabilty can be maintained across your environment.

WHAT IS KEEPALIVED

keepalived is a system daemon in Linux systems that provides frameworks for both high availability and load balancing.

IMPORTANT TERMINOLOGY

1. VIP — Virtual IP, a virtual IP address able to automatically switch between the servers in case of a failure.
2. Master — a server the VIP is currently active on.
3. Backup — a server the VIP will switch to in case of a Master failure.
4. VRID — Virtual Router ID.

IMPORTANT CONCEPTS

1. Basic operation algorithm: at fixed intervals, the Master server sends VRRP packets (heartbeats) to the specific multicasting address 224.0.0.18, and all slave server listen to this address.
2. If a Backup Server does not receive any heartbeat packets, it starts the Master selection procedure.

In this example, I go through the process of configuring keepalived on 2 Red Hat CentOS boxes.

REQUIREMENTS

1. Lab environronment & 2 running instances of CentOS 7 LVS.

DEPLOYMENT PROCESS OVERVIEW

1. Install keepalived
2. Configure Master Server keepalived.conf File
3. Configure Backup Server keepalived.conf File
4. Verify Configuration

TIME TO IMPLEMENT: 15 minutes

INSTALL KEEPALIVED

1. First, run the following commands to make sure everything is up to date/upgraded.

sudo yum -y update

sudo yum -y upgrade

2. Run the following command to install keepalived

sudo yum -y install keepalived

CONFIGURATION OVERVIEW

Note: in this example we are configuring 2 Linux Virtual Servers with keepalived. keepalived uses /etc/keepalived/keepalive.conf as its primary configuration file. In this file, we will need specifiy the following on each server:

1. Router ID - unique identifier for the server.
2. State - state of server (Master of Slave).
3. Priority - what server has priority (highest is selected as Master)
4. Authentication - type of authentication (PASS) and what password.
5. VIP - Virtual IP Address.

CONFIGURE THE KEEPALIVED.CONF FILE [MASTER SERVER]

1. Open the keepalive.conf file in vim on LVS1 by issuing the following command:

sudo vim /etc/keepalived/keepalive.conf

2. In /etc/keepalived/keepalive.conf configuration file, you need to specify the following:

#MASTER SERVER
global_defs {
    notification_email {
        andrew@haratine.net
    }
    notification_email_from andrew@haratine.net
    smtp_server 127.0.0.1
    smtp_connect_timeout 30
    router_id main_server
}
vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    nopreempt
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass passwordhere
    }

    virtual_ipaddress {
        # virtual IP address
        10.10.10.10
    }
}

3. Feel free to add additional configurations, as noted under global_defs. Save and close keepalive.conf file.
4. Run the following commmands to start the daemon:

systemctl enable keepalived
systemctl start keepalived

CONFIGURE THE KEEPALIVED.CONF FILE [BACKUP SERVER]

1. Open the keepalive.conf file in vim on LVS1 by issuing the following command:

sudo vim /etc/keepalived/keepalive.conf

2. In /etc/keepalived/keepalive.conf configuration file, you need to specify the following:

#BACKUP SERVER
global_defs {
    notification_email {
        andrew@haratine.net
    }
    notification_email_from andrew@haratine.net
    smtp_server 127.0.0.1
    smtp_connect_timeout 30
    router_id backup_server
}
vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 51
    priority 99
    nopreempt
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass passwordhere
    }

    virtual_ipaddress {
        # virtual IP address
        10.10.10.10
    }
}

3. Save and close keepalive.conf file.
4. Run the following commmands to start the daemon:

systemctl enable keepalived
systemctl start keepalived 

VERIFY CONFIGURATIONS

1. To test the configuration, run the following command on both machines:

sudo systemctl status keepalived

SUMMARY

1. Minimal congiruation is needed to configure high availibility.
2. Attention to detail is key: ensure the Backup server has a lower priority than the Master, the STATE is set appropriately, and the VIP is not being used by another DHCP host in your environment.
3. To be sure, keepalived is a great option if you are considering high availability for your critical infrastructure.

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