How to do URL based load balancing on F5

There are many load balancers out there. Some of them offer a great flexibility to control the traffic by allowing a user to upload a custom script that implement the load balancing algorithm to solve a particular problem.

Problem

How to do HTTP URL based load balancing on F5.

Solution and demonstration

This is an iRule script that inspects the HTTP GET URL string to decided where to load balance it: https://github.com/rtomaszewski/f5/blob/master/lb-based-on-url.tcl.

Create default pool

	# default pool
	create ltm pool pool-vip-80
	modify ltm pool pool-vip-80 members add { 1.1.1.1:80 { session disabled state down } }
	modify ltm pool pool-vip-80 monitor http
	# let' add some cloud servers manually
	modify ltm pool pool-vip-80 { members add { 10.208.1.1:80 } }
	# use the Rackconnect metadata feature
	# http://www.rackspace.com/knowledge_center/article/using-dedicated-load-balancers-with-rackconnect

view raw default-pool.sh hosted with ❤ by GitHub

Create VIP

	# http vip
	create ltm virtual vs-vip-80 destination 192.168.199.111:http
	modify ltm virtual vs-vip-80 { profiles replace-all-with { tcp { } } }
	modify lmt virtual vs-vip-80 { profiles add { http } }
	modify ltm virtual vs-vip-80 { pool pool-vip-80 }

view raw vip-http.sh hosted with ❤ by GitHub

Create custom pools

	create ltm pool pool-vip-80-url1
	modify ltm pool pool-vip-80-url1 members add { 1.1.1.1:80 { session disabled state down } }
	modify ltm pool pool-vip-80-url1 monitor http
	modify ltm pool pool-vip-80-url1 { members add { ip:port } }
	create ltm pool pool-vip-80-url2
	modify ltm pool pool-vip-80-url2 members add { 1.1.1.1:80 { session disabled state down } }
	modify ltm pool pool-vip-80-url2 monitor http
	modify ltm pool pool-vip-80-url2 { members add { ip:port } }
	create ltm pool pool-vip-80-url3
	modify ltm pool pool-vip-80-url3 members add { 1.1.1.1:80 { session disabled state down } }
	modify ltm pool pool-vip-80-url3 monitor http
	modify ltm pool pool-vip-80-url3 { members add { ip:port } }

view raw custom-pools.sh hosted with ❤ by GitHub

Testing

To verify that our iRule is working properly we can enable debugging by changing the iRule variable DEBUG to 1.

Next we can simulate traffic

curl -v http://vip/
curl -v http://vip/url1
curl -v http://vip/url2
curl -v http://vip/url3

And watch the logs on the lb.

tail -f /var/log/ltm

Mar  2 15:49:37 local/tmm1 info tmm1[5232]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': HTTP::uri eq /
Mar  2 15:49:37 local/tmm1 info tmm1[5232]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': sent traffic to pool pool-vip-80
Mar  2 15:49:37 local/tmm info tmm[5231]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': HTTP::uri eq /url1
Mar  2 15:49:37 local/tmm info tmm[5231]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': sent traffic to pool pool-vip-80-url1
Mar  2 15:49:37 local/tmm1 info tmm1[5232]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': HTTP::uri eq /url2
Mar  2 15:49:37 local/tmm1 info tmm1[5232]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': sent traffic to pool pool-vip-80-url2
Mar  2 15:49:37 local/tmm1 info tmm1[5232]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': HTTP::uri eq /url3
Mar  2 15:49:37 local/tmm1 info tmm1[5232]: Rule rule-url-lb-vip-80 <HTTP_REQUEST>: '11.22.33.44': sent traffic to pool pool-vip-80-url3

Reference

https://devcentral.f5.com/wiki/iRules.HomePage.ashx