What could you do with your code in 20 Lines or Less?
That's the question we like to ask from, for, and of (feel free to insert your favorite preposition here) the DevCentral community, and every time we do, we go looking to find cool new examples that show just how flexible and powerful iRules can be without getting in over your head. Thus was born the 20LoL (20 Lines or Less) series many moons ago. Over the years we've highlighted hundreds of iRules examples, all of which do downright cool things in less than 21 lines of code.
Security Headers
At RSA a couple weeks ago I presented on how to secure your clients with regards to their experience on your web applications. Scott Helme created the SecurityHeaders.io site where you can test your apps to see what is and isn’t supported currently. I can’t stress enough how important it is to read carefully and test thoroughly before implementing some of these headers, you can dos yourself fairly easily. That said, putting in the work to protect your users is a worthy effort, and it’s a pretty easy implementation with iRules, or with an LTM policy.
Redirect the NXDOMAIN Response
We haven't featured too many DNS-based iRules, but we are starting to see an uptick in their presence in the community. The result of the conversation between dearsanky and Kai Wilke is a short but sweet sample redirecting non-existent domain queries
DNS Recursion & Blacklisting
Another more complex DNS sample, also a result of an exchange between dearsanky and Kai Wilke. This iRule blocks queries not configured in the admin_datagroup data-group as well as looks for blacklisted ip’s and blocks those as well. Before the DNS namespace was added to iRules (note: license required if you don’t have GTM/BIG-IP DNS) this was an exercise in binary scans and formats, but is made far simpler with clear commands.
And there it is, another edition of 20 Lines or Less, the power of iRules on full display. Happy coding out there, and I look forward to seeing what excellent contributions might make the next edition!