Latest

Sunday, 19 August 2018

Configure Floating IP with KeepAlived on CentOS 7

keepalived-configure-floating-ip-in-centos-7-servers

In this article, we will configure a Floating IP address for the cluster of two web servers by using KeepAlived.

 

Table of Contents:

 

What is Floating IP Address? :

Floating IP address is used to support failover in a high-availability cluster. The cluster is configured such that only the active member of the cluster "owns" or responds to that IP address at any given time. Should the active member fail, then "ownership" of the floating IP address would be transferred to a standby member to promote it as the new active member. Specifically, the member to be promoted issues a gratuitous ARP, announcing the new MAC address–to–IP address association.

keepalived-configure-floating-ip-in-centos-7-servers

What is KeepAlived? :

Keepalived is a routing software written in C. The main goal of this project is to provide simple and robust facilities for loadbalancing and high-availability to Linux system and Linux based infrastructures. Loadbalancing framework relies on well-known and widely used Linux Virtual Server (IPVS) kernel module providing Layer4 loadbalancing. Keepalived implements a set of checkers to dynamically and adaptively maintain and manage loadbalanced server pool according their health. On the other hand high-availability is achieved by VRRP protocol. VRRP is a fundamental brick for router failover. In addition, Keepalived implements a set of hooks to the VRRP finite state machine providing low-level and high-speed protocol interactions. Keepalived frameworks can be used independently or all together to provide resilient infrastructures.

KeepAlived performs well with haproxy load balancers. Have a look at our article on how to install and configure haproxy load balancer on CentOS 7.

 

System Specification:

We have two webservers webserver-01.centlinux.com and webserver-02.centlinux.com.

Hostname webserver-01.centlinux.com webserver-02.centlinux.com
IP Address 192.168.116.31/24 192.168.116.32/24
Operating System CentOS 7 CentOS 7
Web Server Nginx Nginx

Floating IP Address: 192.168.116.50/24

To ensure that our webservers are properly configured and browsable, open their URLs in a Browser.

Webserver-01 Main PageWebserver-02 Main Page

I have set different index pages on both servers, to differentiate between servers, when we are accessing them via the Floating IP address.

 

Configure KeepAlived on webserver-01:

Connect to webserver-01.centlinux.com and install keepalived by using yum command.

# yum install -y keepalived

Set Linux Kernel parameters as follows to support Floating IP.

# echo "net.ipv4.ip_nonlocal_bind = 1" >> /etc/sysctl.conf

# sysctl -p
net.ipv4.ip_nonlocal_bind = 1

Now configure keepalived settings.

# cd /etc/keepalived/
# mv keepalived.conf keepalived.conf.org
# vi keepalived.conf

Add following directives and save.

! Configuration File for keepalived

global_defs {
   notification_email {
  root@webserver-01.centlinux.com
   }
   notification_email_from root@webserver-01.centlinux.com
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
}

vrrp_instance VI_1 {
    state MASTER
    interface eno16777728
    virtual_router_id 51
    priority 101 #used in election, 101 for master & 100 for backup
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.116.50/24
    }
}

Start and enable keepalived service.

# systemctl start keepalived ; systemctl enable keepalived
ln -s '/usr/lib/systemd/system/keepalived.service' '/etc/systemd/system/multi-user.target.wants/keepalived.service'

Check IP Address of the server.

# ip addr | grep "inet" | grep "eno16777728"
    inet 192.168.116.31/24 brd 192.168.116.255 scope global eno16777728
    inet 192.168.116.50/24 scope global secondary eno16777728

You might observe that the Floating IP: 192.168.116.50 has been assigned to the network interface.

 

Configure KeepAlived on webserver-02:

Connect to webserver-02.centlinux.com and install keepalived by using yum command.

# yum install -y keepalived

Set Linux Kernel parameters as follows to support Floating IP.

# echo "net.ipv4.ip_nonlocal_bind = 1" >> /etc/sysctl.conf

# sysctl -p
net.ipv4.ip_nonlocal_bind = 1

Now configure keepalived settings.

# cd /etc/keepalived/
# mv keepalived.conf keepalived.conf.org
# vi keepalived.conf

Add following directives and save.

! Configuration File for keepalived

global_defs {
   notification_email {
  root@webserver-02.centlinux.com
   }
   notification_email_from root@webserver-02.centlinux.com
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
}

vrrp_instance VI_1 {
    state BACKUP
    interface eno16777728
    virtual_router_id 51
    priority 100 #used in election, 101 for master & 100 for backup
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.116.50/24
    }
}

Start and enable keepalived service.

# systemctl start keepalived ; systemctl enable keepalived
ln -s '/usr/lib/systemd/system/keepalived.service' '/etc/systemd/system/multi-user.target.wants/keepalived.service'

Check IP Address of the server.

# ip addr | grep "inet" | grep "eno16777728"
    inet 192.168.116.32/24 brd 192.168.116.255 scope global eno16777728
    inet 192.168.116.50/24 scope global secondary eno16777728

You might observe that the Floating IP: 192.168.116.50 has been assigned to the network interface.

 

Testing KeepAlived Configuration:

Open the Floating IP Address http://192.168.116.50 in a browser.

Webserver-01 Main Page Through Floating IP

Refresh webpage multiple times, and you will always get the result from same server i.e. webserver-01.centlinux.com.

Now, make webserver-01.centlinux.com unavailable by disconnecting its network connection.

# nmcli c down eno16777728

Again Refresh your webpage.

Webserver-02 Main Page Through Floating IP

You can see that, due to unavailability of webserver-01.centlinux.com the Floating IP is now moved to webserver-02.centlinux.com.

 

Conclusion:

We have successfully configured Floating IP by using KeepAlived in CentOS 7. This aricle is written completely in commandline environment, therefore if you feel any difficulty, then you should buy and read The Linux Command Line, 2nd Edition: A Complete Introduction by William Shotts.

If you find this article useful? Consider supporting us by Buy Me A Coffee


13 comments:

  1. very useful thanks alot

    ReplyDelete
  2. Great explanation sir. Thankyou

    ReplyDelete
  3. small doubt after you moving the keepalived conf file from that path after that how you can open the .conf file from same path.

    [root@webserver-02 ~]# cd /etc/keepalived/
    [root@webserver-02 keepalived]# mv keepalived.conf keepalived.conf.org
    [root@webserver-02 keepalived]# vi keepalived.conf (how can you open it from hear after .conf file is moved to keepa;ived.conf.org)

    ReplyDelete
    Replies
    1. Hi,
      The vi command creates an empty file and then we are adding configurations in it.
      Hope it clarifies your doubt.

      Delete
  4. Hello,

    First of all, thank you for this valuable post.

    I think you should change the parameter "state MASTER" in webserver-02 server to "state BACKUP"

    ReplyDelete
    Replies
    1. Thanks for the correction.
      The same has been updated above.

      Delete
  5. Hello, I am facing a problem with MASTER and BACKUP configuration. My MASTER interface in the "keealived.conf" is different than my BACKUP interface. Like your both MASTER and BACKUP interface name are same "interface eno16777728". So my setup is not working and browser not able to open page using Virtual IP. Any suggestion would be greatly appreciated.

    ReplyDelete
    Replies
    1. By using nmcli, Rename your interfaces on the BACKUP system same as of MASTER.

      Delete
  6. Could you please provide me the complete command as I am not expert on this. Thanks a lot!!

    ReplyDelete
    Replies
    1. Execute following two commands.

      # nmcli c del ens160
      # nmcli c add conn-name ens192 ifname ens160 type ethernet autoconnect yes

      Please discuss it with me on Facebook, if the problem stand still.

      Delete
  7. I ran the command into MASTER: nmcli dev status
    DEVICE TYPE STATE CONNECTION
    ens192 ethernet connected ens192

    I ran the command into BACKUP: nmcli dev status
    DEVICE TYPE STATE CONNECTION
    ens160 ethernet connected ens160



    ReplyDelete
  8. Thanks!! I was missing "echo "net.ipv4.ip_nonlocal_bind = 1" >> /etc/sysctl.conf" step. Now it's working and I understand how it works better.

    ReplyDelete

© 2022 CentLinux. All Rights Reserved.