SNAT persistency

WOW! I will look into that and give it a try.

In the meantime I found some bugs in our iRule:

1. The assignment of snatpool_member as a key to a username doesnt get refreshed. so there are case where an already assigned SNAT IP will be assign to other username.

2. in case there are no more available IPs in the SNAT pool the F5 would still assign the last IP in the pool.

I updated the iRule to address those 2 issues.

Would appreciate if you have ideas for more improvements (maybe it's better to split to 2 tables?)

 when HTTP_REQUEST { 
Set var with the header name used to persist the SNAT IP.
set headername "username" 
Set var with the value of the header name used to persist the SNAT IP.
set headervalue [HTTP::header $headername] 
Set var with the data group name (class) that contains all the SNAT IPs to choose from (data group must be of type string, and include only strings without values).
set clname "snatpool_example" 
Set var with the search id which is used to search the data group. 
set searchID [class startsearch $clname ] 
Set var with the SNAT pool name. the SNAT pool must contain same members as the data group.
set mysnatpool "snatpool_example" 
The snattable var contains the snattable name, if you want to call it something else change it here. 
set snattable "snattable"
Set var used for exiting the while loop in case an available SNAT IP is found.
set match 0 
Set var used for aging time of each table entry
set timeout 180
Check to see if the headervalue already has a SNAT IP .
if { [table lookup -subtable $snattable $headervalue] ne "" } { 
Headervalue already has SNAT IP --> persist using same SNAT IP and restart entry aging time (no "-notouch").
set snatpool_member [table lookup -subtable $snattable $headervalue]
table set -subtable $snattable $snatpool_member $headervalue $timeout
set match 1
} else { 
Headervalue doesn't have SNAT IP --> choose new available SNAT IP from pool.
Go over the data group that contains all the SNAT IPs until an available IP is found.
while { ([class anymore $clname $searchID]) and ($match eq 0) } { 
Set var with the next element (SNAT IP) from the data group.
set snatpool_member [class nextelement -name $clname $searchID] 
Assign the SNAT IP only if it is not already assigned to other.
if { [table lookup -subtable $snattable -notouch $snatpool_member] eq "" } { 
add snat assignement to tables
table set -subtable $snattable $snatpool_member $headervalue $timeout
table set -subtable $snattable $headervalue $snatpool_member $timeout
local log entry this should be changed to a highspeed log off box. 
log local0.info "SNAT assignment: $headervalue --> $snatpool_member"
exiting the while loop as an available SNAT IP is found.
set match 1 
} 
} 
}
if {[class anymore $clname $searchID] eq 1 } {
snatpool $mysnatpool member $snatpool_member 
log local0.info "SNAT action: $headervalue --> $snatpool_member"
HTTP::header remove $headername
} else {
log local0.info "There are no more available SNAT IPs!!!"
}
}