iRule syntax problems

A couple of points.

1) remove the "rule" enclosure unless you are editing from the configuration file directly.

2) use "elseif" instead of "else if".

when HTTP_REQUEST {
  if { [HTTP::host] eq "mysite1.com" } {
    pool mysite1.com
  } elseif { [HTTP::host] eq "mysite2.com" } {
    pool mysite2.com
  } elseif { [HTTP::host] eq "mysite3.com" } {
    pool mysite3.com
  } elseif { [HTTP::host] eq "mysite4.com" } {
    pool mysite4.com
  } elseif { [HTTP::host] eq "mysite5.com" } {
    pool mysite5.com
  } elseif { [HTTP::host] eq "mysite6.com" } {
    pool mysite6.com
  } elseif { [HTTP::host] eq "mysite7.com" } {
    pool mysite7.com
  } else { 
    discard
  }
}

You could also make this much cleaner by using an external data group (do a search for matchclass/findclass in the forums).

-Joe