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Forum Discussion

Robert_Sutcliff's avatar
Robert_Sutcliff
Icon for Nimbostratus rankNimbostratus
Dec 03, 2009

How random is rand()?

Hi,   How random is the tcl rand function?     We're currently using it to generate a unique(ish) value for each request we process - using a code bloc like this     se...
application delivery
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iRules
Robert_Sutcliff's avatar
Robert_Sutcliff
Icon for Nimbostratus rankNimbostratus
Dec 04, 2009
A solution I've come up with is to use a STATS profile.

 

Then for every connection (on every vhost) we can increment a counter. The code snippet then becomes

 

 

 
   set iruleversion [format "%04X" 1] 
   set F5id "[format "%02X" 1]" 
   STATS::incr Booking_stats request_count 
   set rnum [format "%08X" [STATS::get Booking_stats request_count] ] 
   set cthash [format "%08X" [clock seconds] ] 
   set tracker "$F5id$iruleversion$cthash$rnum"

 

 

This allows us to identify the BigIP pair (F5id) the request was processed by, and gives us a version number (iruleversion) for the iRule, which together with the clock should ensure we don't get duplicate values if/when the Booking_stats profile is reset.

 

Unfortunately the F5id and iruleversion need manual control, but as I don't think we'll be updating either frequently this isn't a problem.

 

 

Rob