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?
- What is KeepAlived?
- System Specification
- Configure KeepAlived on webserver-01
- Configure KeepAlived on webserver-02
- Testing KeepAlived Configuration
- Conclusion
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.
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.
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.
[root@webserver-01 ~]# yum install -y keepalived
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
localyum | 4.1 kB 00:00
Resolving Dependencies
--> Running transaction check
---> Package keepalived.x86_64 0:1.2.10-2.el7 will be installed
--> Processing Dependency: libnetsnmp.so.31()(64bit) for package: keepalived-1.2.10-2.el7.x86_64
--> Processing Dependency: libnetsnmpagent.so.31()(64bit) for package: keepalived-1.2.10-2.el7.x86_64
--> Processing Dependency: libnetsnmpmibs.so.31()(64bit) for package: keepalived-1.2.10-2.el7.x86_64
--> Running transaction check
---> Package net-snmp-agent-libs.x86_64 1:5.7.2-18.el7 will be installed
---> Package net-snmp-libs.x86_64 1:5.7.2-18.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
keepalived x86_64 1.2.10-2.el7 localyum 218 k
Installing for dependencies:
net-snmp-agent-libs x86_64 1:5.7.2-18.el7 localyum 698 k
net-snmp-libs x86_64 1:5.7.2-18.el7 localyum 745 k
Transaction Summary
================================================================================
Install 1 Package (+2 Dependent packages)
Total download size: 1.6 M
Installed size: 5.6 M
Downloading packages:
--------------------------------------------------------------------------------
Total 2.6 MB/s | 1.6 MB 00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : 1:net-snmp-libs-5.7.2-18.el7.x86_64 1/3
Installing : 1:net-snmp-agent-libs-5.7.2-18.el7.x86_64 2/3
Installing : keepalived-1.2.10-2.el7.x86_64 3/3
Verifying : 1:net-snmp-libs-5.7.2-18.el7.x86_64 1/3
Verifying : 1:net-snmp-agent-libs-5.7.2-18.el7.x86_64 2/3
Verifying : keepalived-1.2.10-2.el7.x86_64 3/3
Installed:
keepalived.x86_64 0:1.2.10-2.el7
Dependency Installed:
net-snmp-agent-libs.x86_64 1:5.7.2-18.el7 net-snmp-libs.x86_64 1:5.7.2-18.el7
Complete!
Set Linux Kernel parameters as follows to support Floating IP.
[root@webserver-01 ~]# echo "net.ipv4.ip_nonlocal_bind = 1" >> /etc/sysctl.conf
[root@webserver-01 ~]# sysctl -p
net.ipv4.ip_nonlocal_bind = 1
[root@webserver-01 ~]#
Now configure keepalived settings.
[root@webserver-01 ~]# cd /etc/keepalived/
[root@webserver-01 keepalived]# mv keepalived.conf keepalived.conf.org
[root@webserver-01 keepalived]# 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.
[root@webserver-01 keepalived]# 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.
[root@webserver-01 keepalived]# 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
[root@webserver-01 keepalived]#
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.
[root@webserver-02 ~]# yum install -y keepalived
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
localyum | 4.1 kB 00:00
nginx | 2.9 kB 00:01
rpmforge | 1.9 kB 00:00
Resolving Dependencies
--> Running transaction check
---> Package keepalived.x86_64 0:1.2.10-2.el7 will be installed
--> Processing Dependency: libnetsnmp.so.31()(64bit) for package: keepalived-1.2.10-2.el7.x86_64
--> Processing Dependency: libnetsnmpagent.so.31()(64bit) for package: keepalived-1.2.10-2.el7.x86_64
--> Processing Dependency: libnetsnmpmibs.so.31()(64bit) for package: keepalived-1.2.10-2.el7.x86_64
--> Running transaction check
---> Package net-snmp-agent-libs.x86_64 1:5.7.2-18.el7 will be installed
---> Package net-snmp-libs.x86_64 1:5.7.2-18.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
keepalived x86_64 1.2.10-2.el7 localyum 218 k
Installing for dependencies:
net-snmp-agent-libs x86_64 1:5.7.2-18.el7 localyum 698 k
net-snmp-libs x86_64 1:5.7.2-18.el7 localyum 745 k
Transaction Summary
================================================================================
Install 1 Package (+2 Dependent packages)
Total download size: 1.6 M
Installed size: 5.6 M
Downloading packages:
--------------------------------------------------------------------------------
Total 11 MB/s | 1.6 MB 00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : 1:net-snmp-libs-5.7.2-18.el7.x86_64 1/3
Installing : 1:net-snmp-agent-libs-5.7.2-18.el7.x86_64 2/3
Installing : keepalived-1.2.10-2.el7.x86_64 3/3
Verifying : 1:net-snmp-libs-5.7.2-18.el7.x86_64 1/3
Verifying : 1:net-snmp-agent-libs-5.7.2-18.el7.x86_64 2/3
Verifying : keepalived-1.2.10-2.el7.x86_64 3/3
Installed:
keepalived.x86_64 0:1.2.10-2.el7
Dependency Installed:
net-snmp-agent-libs.x86_64 1:5.7.2-18.el7 net-snmp-libs.x86_64 1:5.7.2-18.el7
Complete!
Set Linux Kernel parameters as follows to support Floating IP.
[root@webserver-02 ~]# echo "net.ipv4.ip_nonlocal_bind = 1" >> /etc/sysctl.conf
[root@webserver-02 ~]# sysctl -p
net.ipv4.ip_nonlocal_bind = 1
Now configure keepalived settings.
[root@webserver-02 ~]# cd /etc/keepalived/
[root@webserver-02 keepalived]# mv keepalived.conf keepalived.conf.org
[root@webserver-02 keepalived]# 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.
[root@webserver-02 keepalived]# 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.
[root@webserver-02 keepalived]# 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
[root@webserver-02 keepalived]#
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.
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.
[root@webserver-01 ~]# nmcli c down eno16777728
Again Refresh your webpage.
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.
very useful thanks alot
ReplyDeleteGreat explanation sir. Thankyou
ReplyDeleteMy pleasure.
Deletesmall doubt after you moving the keepalived conf file from that path after that how you can open the .conf file from same path.
ReplyDelete[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)
Hi,
DeleteThe vi command creates an empty file and then we are adding configurations in it.
Hope it clarifies your doubt.
Hello,
ReplyDeleteFirst of all, thank you for this valuable post.
I think you should change the parameter "state MASTER" in webserver-02 server to "state BACKUP"
Thanks for the correction.
DeleteThe same has been updated above.
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.
ReplyDeleteBy using nmcli, Rename your interfaces on the BACKUP system same as of MASTER.
DeleteCould you please provide me the complete command as I am not expert on this. Thanks a lot!!
ReplyDeleteExecute following two commands.
Delete# 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.
I ran the command into MASTER: nmcli dev status
ReplyDeleteDEVICE TYPE STATE CONNECTION
ens192 ethernet connected ens192
I ran the command into BACKUP: nmcli dev status
DEVICE TYPE STATE CONNECTION
ens160 ethernet connected ens160
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