Need help with my iRules, basically i am trying to calculate the time take when the F5 receives a request and sends it to the client. This gives me the time for how long the request took on our side before releasing it to the client. However i have seem some descrepancies with certain requests.
Setup:
I have two load balancers, there are two iRules and on each load balancer the time taken is calculated and the value sent as a header back in the response.
The traffic flow is as follows
Internet User -> Load balancer 1 -> Load balancer 2 -> Backend servers
iRule on Load balancer 1:
ltm rule LoadBalancer1 {
when HTTP_REQUEST {
#Record the time when request event in this iRule is triggered
set http_request_time [clock clicks -milliseconds]
}
when HTTP_RESPONSE_RELEASE {
#Record the time when response is ready to be released to the client side
set http_responserelease_time [clock clicks -milliseconds]
set time_taken [expr {$http_responserelease_time - $http_request_time}]
#set response headers for client side analysis
HTTP::header replace "LoadBalancer1-TimeTaken" "$time_taken ms"
#unset the variables
unset http_responserelease_time http_request_time time_taken
}
}
iRule on Load balancer 2:
ltm rule LoadBalancer2 {
when HTTP_REQUEST {
#Record the time when request event in this iRule is triggered
set http_request_time [clock clicks -milliseconds]
}
when HTTP_RESPONSE_RELEASE {
#Record the time when response is ready to be released to the client side
set http_responserelease_time [clock clicks -milliseconds]
set time_taken [expr {$http_responserelease_time - $http_request_time}]
#set response headers for client side analysis
HTTP::header replace "LoadBalancer2-TimeTaken" "$time_taken ms"
#unset the variables
unset http_responserelease_time http_request_time time_taken
}
}
Problem:
Assuming my above setup is correct, then the value of header LoadBalancer1-TimeTaken should be greater than LoadBalancer2-TimeTaken for each of the HTTP requests sent during a page load.
Though i see this to be true (LoadBalancer1-TimeTaken > LoadBalancer2-TimeTaken) for most of the requests, some requests it is the other way (LoadBalancer2-TimeTaken > LoadBalancer1-TimeTaken) I have noticed this for some javascript files, from my observation it seems consistent for the same javascript files. How is this possible?
