f5 Hiccup with new iRule

Here is an article which explains what you saw:

 

http://devcentral.f5.com/Tutorials/TechTips/tabid/63/articleType/ArticleView/articleId/130/iRules-101--05--Selecting-Pools-Pool-Members-and-Nodes.aspx

 

 

The short version is that you matched on "/image/" and your next request didn't match on "/mrocache/mrosupply_data.xml". Your rule without that final else statement used the last pool it had selected, the mroimage pool. Adding a final "else" catches anything that didn't match earlier in your rule and ensures that mrosupply-pool is selected if nothing else matches.