Centos 7/RHEL 7 LVS HAPROXY KEEPALIVED

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Presentation

For this tutorial, 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 with HAProxy and keepalived. For this reason, HAProxy will be used as load-balancing software, keepalived as high availability solution and apache as software to load-balance.

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
HAProxy Installation

On the haproxy1/haproxy2 servers, execute the following instructions:

Install the HAProxy package:

# yum install -y haproxy
Edit the /etc/haproxy/haproxy.cfg file, replace the line “frontend main *:5000” with “frontend main *:80” and comment out the line “use_backend static if url_static“.
At 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
Create the /etc/firewalld/services/haproxy.xml file and paste the following lines:

HAProxy
HAProxy load-balancer

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

On the haproxy1/haproxy2 servers, execute the following instructions:

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
}
}
Activate at boot and start the keepalived service:

# systemctl enable keepalived
# systemctl start keepalived
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 the instructions for the Apache installation.
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
HAProxy Intricacies

In some cases, because HaProxy tries to bind to an IP address that doesn’t exist on any interfaces, it doesn’t start and displays an error message like “Starting proxy stats: cannot bind socket“.

The solution is to create a file called /etc/sysctl.d/10-haproxy.conf and paste the following line:

net.ipv4.ip_nonlocal_bind=1
Then, update the configuration:

# sysctl -p

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