iRule design considerations for ISA to BigIP migration.

Hi Aaron,

 

 

Thanks for taking the time to reply.

 

 

I suppose key considerations will be:

 

 

1. Minimise the number of ASM policies. I don't think we can limit it to one as there may be different application backends to tailor for - unless a decision is made to provide a very "light" policy which isn't app specific. I think the iRule may have become a little more complicated as I have seen evidence that we have a combination of the following:

 

 

http://URL/someuri is replaced with http://URL/somecompletelydifferenturi

 

and

 

http://URL/anotheruri is prepended with http://URL/prepend/anotheruri

 

 

A coder may look at this and think that's easy. I have an idea on how it might work but not sure if it's a valid one or not. My thought would be that the prepend is treated the same as the replace, and given the example from my second post to this topic, the "right" URI string in the DGL will simply replace the "left" string in the DGL, rather than trying to make a decision on whether it's a rewrite or a replace. But then I think you could make a decision on whether it's a rewrite or a prepend and execute the appropriate section of the iRule. The thing that leads me away from that idea though is the actual decision requirement to begin with, as it starts to complicate things imho.

 

 

2. The iRule and associated DGL (probably just the latter) need to be easy to update. Unfortunately the state of the environment is that the devices are under the administrative control of people who don't really know too much about application delivery and are more often thought of as 'data entry' types. Sometimes we might find a diamond or two in the rough but getting consistent access to these resources is difficult at best. Given your comments though regarding making the LB decision within the iRule, rather than a pool on an HTTP class, would require updates to the iRule which I'm tempted to avoid if possible.

 

 

3. Whilst I'd love to engage an F5 SE, I'm not quite sure how to go about it in the UK. To date we've always dealt with a third-party supplier. Given our size, it's not very easy to get funding approved to bring in the third-party and I'm told the project hasn't allocated any budget to do so. Doh! Also in recent times it's become a little harder to obtain some pro-bono consultancy as some of their long-serving consultants have moved on. We're not a small F5 shop to be honest. We have 40+ devices, most of which are at least 6400's and a fair few 8400's so I wonder how we could engage F5 directly?

 

 

Thanks for the heads up on the main iRule thread. I wanted to avoid to "main" line for now as I wasn't trying to write code (something I feel I need to start learning how to do and quickly) but rather just get an idea on how an iRule developer might tackle this migration.

 

 

Sorry for the long post but I appreciate your time.

 

 

Cheers,

 

Packeteer.