Friday, October 28, 2011

Deploying a loadbalanced Apache front end

This particular configuration is being used to support a large Moodle Installation.
The front end comprises of:
1 Loadbalancer
3 webservers
The load balancer virtual IP

Prerequisites:
Fully built and configured CentOS Apache-based webservers
One clean CentOS server to act as loadbalancer

IP's
Webserver 1- 192.168.100.1
Webserver 2 - 192.168.100.2
Webserver 3- 192.168.100.3
Loadbalancer - 192.168.100.5
Virtual IP- 192.168.100.10

On Each Webserver

1.         Open Terminal Interface
2.         Create  specific test file on each webserver to allow the Loadbalancer to check.
echo foo >  /var/www/html/test.html

3.        Create unique identifiers on each webserver to ensure the load balancing algorithm works. These files will be deleted later on.
On each webserver x (replace x with associated number)
echo "This is  Webserver X" > /var/www/html/index.html

4.         Create a loopback interface with the virtual IP to terminate on each webserver:
nano /etc/sysconfig/network-scripts/ifcfg-lo:0
DEVICE=lo:0
IPADDR=192.168.100.20
NETMASK=255.255.255.255
ONBOOT=yes
NAME=loopback

5.        Configure kernel to announce ARP requests/send responses
nano /etc/sysctl.conf
Modify the following entries
net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.eth0.arp_ignore = 1
net.ipv4.conf.all.arp_announce = 2
net.ipv4.conf.eth0.arp_announce = 2

6.        Reload modified kernel parameters and bring up loopback:
sysctl -p
ifup lo:0

On the Loadbalancer

1.        Open command line
2.        Install necessary packages
yum install -y heartbeat heartbeat-ldirectord ipvsadm

3.         Configure ldirectord and heartbeat in autostart list.
chkconfig --add ldirectord
chkconfig --del heartbeat

4.     Modify kernel to allow IP forwarding
nano /etc/sysctl.conf
find the following parameter:
net.ipv4.ip_forward = 0
change the parameter:
net.ipv4.ip_forward = 1
5.     Reload modified kernel parameter:
sysctl -p

6.        Configure secondary ethernet interface for Virtual IP:
nano /etc/sysconfig/network-scripts/ifcfg-eth0:0
DEVICE=eth0:0
BOOTPROTO=none
ONBOOT=yes
HWADDR=3a:5d:23:ad:67:47 <>
NETMASK=255.255.255.0
IPADDR=192.168.100.10
GATEWAY=192.168.100.1
TYPE=Ethernet




7.        Create ldirector configuration file:
nano /etc/ha.d/ldirectord.cf
checktimeout=10
checkinterval=2
autoreload=no
logfile="/var/log/ldirectord.log"
quiescent=no
virtual=192.168.100.10:80
               real=192.168.100.1:80 gate
               real= 192.168.100.2:80 gate
               real= 192.168.100.3:80 gate
               service=http
               request="test.html"
               receive="foo"
               scheduler=wlc
               protocol=tcp
               checktype=negotiate
8.         Restart the ldirectord service:
service ldirectord restart
9.     Test the configuration:
ipvsadm -l
Expected output:
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
 -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  yoursite.com:http wlc
 -> web03:http   Route   1      412        0
 -> web02:http   Route   1      411        0
 -> web01:http   Route   1      411        0



That should be it! Your DNS may need to be configured to point your external IP to the Virtual IP.

-n

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