How to learn and write iRule

There are several sources for learning iRules, including a couple of tutorials right here on DevCentral. Start at the iRules Wiki Home page, perhaps with the iRules101 course by Jason Rahm, one of F5's resident iRules experts. There is also some free training available at F5 University in the Getting Started Series, specifically Getting Started with BIG-IP LTM: Part 2 - iRules and Accelerating Traffic.

Finally, if you really want an intensive iRules course, there's our Developing iRules for BIG-IP 3-day instructor-led course. You can find out where that course is scheduled to be delivered here.