sample irule for redirect / rewrite

Well, in a redirect iRule, and especially the one above, the client (browser) would change the host header for you. In fact the host header might only ever need to be changed en route to the server if the server expects (and requires) a different host header than what the client is providing. It's a little difficult to give you any sort of solid example without knowing what you're trying to achieve. In any case, think of a data group as a set of key-value pairs, where the key is usually something the client is providing (host name, URI part, cookie, anything really), and the value is what you want to translate that to. The above example took the request URI and translated that into a host name for a physical (302) redirect. It could as easily have been a translation to a different URI, both explicitly through a redirect, or by simply changing the URI (or part of it) in line, without the user's knowledge.