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smp_86112's avatar
smp_86112
Icon for Cirrostratus rankCirrostratus
Jan 03, 2014
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Short iRule rewrite for efficiency/readability

I have a short iRule that is simple to understand. Logically, the iRule works by checking the host header against two known values and modifies the Host: header if neither match. This is how it's currently written:

when HTTP_REQUEST {
  if { not (( [string tolower [HTTP::host]] equals "myapp1.domain.com" ) or
            ( [string tolower [HTTP::host]] equals "myapp2.domain.com" )) } {
    HTTP::header replace "Host" [HTTP::host]:9070
  }
}

Intuitively it seems this iRule could be written more efficiently, or at least easier to read. Normally I'd do this comparison in a SWITCH statement, but I can't seem to get SWITCH to work with negation. I know that there isn't a lot of efficiency to gain here, but I was hoping someone could give me some ideas on how they would accomplish this same logic?

application delivery
devops
iRules
  • Ben_Wilson_2412's avatar
    Ben_Wilson_2412
    Jan 03, 2014

    Don't know that you need to negate the match, just perform no action on matching "myapp1" or "myapp2" and use the default case to perform your replace.

     

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  • Ben_Wilson_2412's avatar
    Ben_Wilson_2412
    Icon for Cirrus rankCirrus
    Jan 03, 2014

    Don't know that you need to negate the match, just perform no action on matching "myapp1" or "myapp2" and use the default case to perform your replace.

     

  • smp_86112's avatar
    smp_86112
    Icon for Cirrostratus rankCirrostratus
    Jan 03, 2014

    That never occurred to me. Were you thinking of something like this?

    when HTTP_REQUEST {
  switch -- [string tolower [HTTP::host] {
    "myapp1.example.com" -
    "myapp2.example.com" { }
    default { HTTP::header replace "Host" [HTTP::host]:9070 }
  }
}
    • smp_86112's avatar
      smp_86112
      Icon for Cirrostratus rankCirrostratus
      Jan 03, 2014
      I tried this and it worked perfectly, and it makes much more sense to read. Exactly what I was looking for. Don't understand why it didn't occur to me to write it this way, but thanks for the idea!!