How to check for performance in URL Rewriting

Question

I am coming at this from a different angle, probably, but mostly the question I am being asked is if we implement URL Rewrite to handle redirecting older URL's into SharePoint is there a performance hit to our SharePoint 2010 farm? I'm not really sure from a SharePoint view if just checking page load times will suffice, it's what I would check from a regular IIS instance to determine under load if we had a performance problem. Since the question I have to answer is only - will the URL Rewriting cause a problem - I'm not really sure what I could test.

The URL's are basically existing URL's, from the current ASP/IIS site, that will need to redirect to SharePoint url's - getting people from any bookmarked old URL's to the new locations. We only have about 100 of these so it's not an onerous list, but will having URL Rewrite on the Farm mean we will have a performance hit for any requests that do not meet the mapping? I'm a little new to this aspect of SharePoint and URL Rewrite, my belief is that the Mapped URL's are cached and as each request comes in it will be quickly checked then passed on if it doesn't match.

Answer 1

First, it is important to distinguish between rewrites and redirects. The HTTP modules are usually referred to as rewrite modules (e.g. URLRewriter or IIS7 rewrite module), but will do both rewrites (server responds to old URL with content served from new URL and client is none the wiser) and redirects (server returns a 301 or 302 status code and client initiates a second requested to the new URL). Rewrites are not a supported configuration for SharePoint. You are using redirects - good.

To your question: depending on the rewriter and the complexity of the rules, the effect of the rule processing can be significant. Remember that every incoming URL will be compared against the rules, even if none of them apply. You say you have 100 or so redirecting URLs. If you can find generic rules for most of these it should be better than a long list of individual mappings.

My guess is that you will be able to measure some effect on performance, but not enough to be an issue. Rejecting traffic would be far worse. Users coming in on the old URL will see a delay because of the extra round trip, but over time this should be a diminishing number as they update their URLs.

One last point is that if your old ASP.NET URLs have a different domain you don't need to put the rewriter in front of your SharePoint web application at all. You can set up an IIS site with dummy pages and redirects, leaving your SharePoint virtual server unadulterated.

Answer 2

This might not be the same, but I think it's something worth looking at to give you some additional information. It describes how nothingbutsharepoint.com used IIS7.5 to create 301 redirects from old domains to new domains.