iRule: generic host to uri mapping

The question came in on DevCentral asking how to dynamically map the company within the host portion of the HTTP request to cause a redirect to a custom uri starting with that company name.

I'm in a web hosting environment and I've got a situation where I need to do URL rewrites for the each customer on the BigIP.

http://www.A.com/ ---> http://www.IIS_node.com/A
http://www.B.com/ ---> http://www.IIS_node.com/B
.
.
etc (there's a *significant* number of customers... at least 100)

One could do a very long if/elseif clause but that wouldn't be any fun now would it? I recommended using a regular expression to strip out the company portion of the uri like the following

when HTTP_REQUEST {
  # www.A.com -- domain == A.com, company == A
  regexp {\.([\w]+)\.com} [HTTP::host] domain company
  if { "" ne $company } {
    HTTP::redirect "http://www.my_vs.com/$company"
  }
}

But that could cause unwanted errors if a company is passed in that isn't defined in the backend application. You can get around this by validating the company name with a data group lookup as illustrated below:

*** BEGIN STRING DATA GROUP ***
class valid_company_names {
  "A"
  "B"
  "C"
}
*** END STRING DATA GROUP ***

*** BEGIN RULE ***
when HTTP_REQUEST {
  # www.A.com -- domain == A.com, company == A
  regexp {\.([\w]+)\.com} [HTTP::host] domain company
  if { "" ne $company } {
    if { [matchclass $company equals $::valid_company_names] > 0 } {
      HTTP::redirect "http://www.my_vs.com/$company"
    }
  }
}

And, finally, if there isn't an exact mapping from domain to uri, but you still want to do the mapping cleanly, you could use a string Data Group that contains the mappings. If the company is found in the Data Group, you can extract the mapping portion of the string with the findclass command as follows:

*** BEGIN STRING DATA GROUP ***
class valid_company_mappings {
  "A mapping_for_a"
  "B mapping_for_b"
  "C mapping_for_c"
}
*** END STRING DATA GROUP ***

*** BEGIN RULE ***
when HTTP_REQUEST {
  # www.A.com -- domain == A.com, company == A
  regexp {\.([\w]+)\.com} [HTTP::host] domain company
  if { "" ne $company } {

    # look for the second string in the data group
    set mapping [findclass $company $::valid_company_mappings " "]
    if { "" ne $mapping } {
      HTTP::redirect "http://www.my_vs.com/$mapping"
    }
  }
}

Simple but very powerful iRule if I do say so myself!

See the original forum thread here.

-Joe