SQUID Load balancing for web applications

Squid Load Balancer Configurations

A short note on we have done to make the squid load balancer working
The servers are CEnt OS 5.x

Total machines 2 (Don't ask me why it is 2, This is what I had to test and play with in my lab)
Machine 1 - IPs 192.168.5.50 and 192.168.5.51 (2 LAN cards)
Machine 2 - IPs 192.168.100 and 192.168.5.101 (2 LAN cards)

The machine 1 and 2 Will have Apache application running on them which needs to be load balanced.

Problem: We need a seperate machine which should act as load balancer for both, but we don't have any other machine than these 2.
Solution: Machine 1 will act as load balancer and also as a application server(not adviceable) but can go ahead if we run out of resource as we have no other option.

DNS Names
DOMAIN Name for public access webapp.office.lan

webapp.office.lan - 192.168.5.50
server_1_a.office.lan - 192.168.5.50
server_1_b.office.lan - 192.168.5.51

server_2_a.office.lan - 192.168.5.100
server_2_b.office.lan - 192.168.5.101

The web application is configured in both the server with apache vhosts.


The default site is webapp.office.lan and squid listens to the queries on that.

So the first part is making the application work in

server_1_b.office.lan - 192.168.5.51
server_2_b.office.lan - 192.168.5.101

Configuring apache right to make this work properly.
Since Squid and Apache are going to run on same machine(1) and are to be used in same port number 80 we need to make apache listen only for requests on IP:192.168.5.51

To do the above
Change the httpd.conf
Modify the line
Listen 80
to
Listen 192.168.5.51:80

So apache listens only the IP: 192.168.5.51 on Port 80

Now configure the vhost of the web app accordingly in Apache on IP:192.168.5.51
Verify do the site works by accessing server_1_b.office.lan

Configuring App in server_2_b.office.lan - 192.168.5.101
Since the app is now configured on a different machine we don't need to change the Apache Listen property.
but once configured just check the site works with server_2_b.office.lan URL

Squid in Action
Installing squid in CentOS is as same as installing Apache with yum installer.

Configuring Squid
Add the following lines in /etc/squid/squid.conf

------------------------------ Lines to be added in squid.conf -------------------------------
#Make SQUID Listen on PORT 80
http_port 192.168.5.50:80 defaultsite=webapp.office.lan vhost

# Mapping 192.168.5.51 as server_1
cache_peer server_1_b.office.lan parent 80 0 no-query originserver name=server_1 login=PASS
cache_peer_domain server_1 server_1_b.office.lan login=PASS

# Mapping 192.168.5.101 as server_2
cache_peer server_2_b.office.lan parent 80 0 no-query originserver name=server_2 login=PASS
cache_peer_domain server_2 server_2_b.office.lan login=PASS

cache_peer server_1_b.office.lan parent 80 0 round-robin no-query originserver login=PASS
cache_peer server_2_b.office.lan parent 80 0 round-robin no-query originserver login=PASS

----------------------------- End of lines to be added in squid.conf ----------------------


Now the squid can be restarted.
The server will be listening to webapp.office.lan each request will be diverted to different server based on the round robin flow and if any one fails the other will server the request continuously we can add 'n' servers similar to this to make the count higher
Note all the vhost in the Apache should listen to domain name "webapp.office.lan".

Hope this gave a useful information on SQUID loadbalancing, This is not only for apache but can be any webserver serving similarly.