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

Create VIP

Create custom pools

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