This tutorial explains how to set up a two-node load balancer with HAProxy and keepalived on CentOS 7. The load balancer sits between the user and two (or more) backend Apache web servers that hold the same content. If one of them is down, all requests will automatically be redirected to the remaining backend server. which means the users will not notice any disruption of the service.
For configuring HA-Load balanceer, You need 2 virtual/physical servers for the load-balancers and 2 virtual/physical servers to load-balance. In addition to the 4 IP addresses needed by the servers themselves, a fifth virtual IP address (VIP) is necessary. The two load-balancers and the VIP need to be in the same network segment.
Piranha has been replaced in RHEL7/CENTOS 7 with HAProxy and keepalived. So, HAProxy will be used as load-balancing software, keepalived as high availability solution and apache as software to load-balance.
Host details:
- Load Balencer 1: haproxy1, IP: 192.168.0.101
- Load Balencer 2: haproxy2, IP: 192.168.0.102
- Web Server 1: httpd1, IP: 192.168.0.103
- Web Server 2: httpd2, IP: 192.168.0.104
We also need a virtual IP address that floats between haproxy1 and haproxy2 : vip, IP: 192.168.0.10
Here is the addressing schema chosen to write into the /etc/hosts file of each server
192.168.0.100 vip 192.168.0.101 haproxy1 192.168.0.102 haproxy2 192.168.0.103 httpd1 192.168.0.104 httpd2
Here’s a little diagram that shows our setup:
shared IP=192.168.0.100
192.168.0.101 192.168.0.102 192.168.0.103 192.168.0.104
——————–+———————+——————-+——————-+
| | | |
+–+–+ +–+–+ +—-+—-+ +—-+—-+
| haproxy1 | | haproxy2 | | httpd1 | | httpd2 |
+—–+ +—–+ +———+ +———+
haproxy haproxy 2 web servers (Apache)
keepalived keepalived
HAProxy installation
On the haproxy1/haproxy2 servers, execute the following instructions:
Install the HAProxy package:
yum install -y haproxy
Open /etc/haproxy/haproxy.cfg file using your favourite editor, Mine is vi, replace the line “frontend main *:5000″ with “frontend main *:80″ and comment out the line “use_backend static if url_static”.
Go to the end of the same file, remove the lines starting with “server app” and replace them with the following lines:
server httpd1 192.168.0.103:80 check server httpd2 192.168.0.104:80 check
Activate at boot and start the HAProxy service:
systemctl enable haproxy systemctl start haproxy
Open /etc/firewalld/services/haproxy.xml file and paste the following lines:
<?xml version="1.0" encoding="utf-8"?> <service> <short>HAProxy</short> <description>HAProxy load-balancer</description> <port protocol="tcp" port="80"/> </service>
Next we need to assign correct SELinux context and file permissions to the haproxy.xml file:
cd /etc/firewalld/services restorecon haproxy.xml chmod 640 haproxy.xml
Update the firewall configuration:
firewall-cmd --permanent --add-service=haproxy firewall-cmd --reload
Keepalived installation
Next, We need to install keepalived on haproxy1 and haproxy2
Install the keepalived package:
yum install -y keepalived
Create a new /etc/keepalived/keepalived.conf file and paste the following lines:
vrrp_script chk_haproxy {
script "killall -0 haproxy" # check the haproxy process
interval 2 # every 2 seconds
weight 2 # add 2 points if OK
}
vrrp_instance VI_1 {
interface eth0 # interface to monitor
state MASTER # MASTER on haproxy1, BACKUP on haproxy2
virtual_router_id 51
priority 101 # 101 on haproxy1, 100 on haproxy2
virtual_ipaddress {
192.168.0.100 # virtual ip address
}
track_script {
chk_haproxy
}
}
Issue following commands to Enable keepalived service on system boot up:
systemctl enable keepalived systemctl start keepalived
Next, we need to Check the presence of the VIP on the haproxy1 server:
# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 52:54:00:f7:2a:a9 brd ff:ff:ff:ff:ff:ff inet 192.168.0.101/24 brd 192.168.0.255 scope global eth0 valid_lft forever preferred_lft forever inet 192.168.0.100/32 scope global eth0 valid_lft forever preferred_lft forever inet6 fe80::5054:ff:fef7:2aa9/64 scope link valid_lft forever preferred_lft forever
Apache installation
On the httpd1/httpd2 servers, follow Install LAMP Server (Apache, MariaDB, PHP) On CentOS/RHEL/Scientific Linux 7 to install apache.
Create a file called index.html in the /var/www/html directory on the httpd1 server and paste the following line:
Test httpd1
Do the same operation on the httpd2 server but replace “httpd1″ with “httpd2″ in the index.html file.
From another server, test the configuration:
yum install -y elinks elinks http://192.168.0.100
Cheers!!
See you next time!!
