Is it normal for F5 LTM CPU to hike 10% extra with iRule implementation?

irules could be CPU intensive depending on commands you are using. Subtables could impact performances.

 

Could you check with show ltm virtual if cmp is still enable on your vs?

 

the following line set client_id [format "%08d" [expr { int(1000000000 * rand()) }]] is requiring resources outside of tmm and cost a lot, even more as you are doing it per request.

 

if you want to count sessions you should move you logic outside http_request to TCP events, but in this case no more cookie usage.

 

could you describe a little bit what you are trying to achieve ?

 

Hi Arnaud,

 

Thanks for your input. I am trying to access a waiting room page via this iRulesonce the website reaches a max number of connections. There is a separate data-group from which this iRule is fetching different values.

 

Yes CMP is enabled on the vs.

 

So there is no way I can put the logic to check the TCP connections rather than sessions?

 

Regards,

 

You can save a bit of CPU cycles by not doing the data group lookups on each HTTP request. You could do this once at config load time by moving the lookups to RULE_INIT:

when RULE_INIT {
    set static::maxActiveClients "[class search -all -value datagroup_selfridges_waitingroom starts_with "max_active_clients"]"
    set static::subtableName "sessionLimit"
    set static::sessionCookieName "[class search -all -value datagroup_selfridges_waitingroom starts_with "session_cookie_prefix"]"
    set static::holdingPage "[class search -all -value datagroup_selfridges_waitingroom starts_with "holding_page_url"]"
    set static::sessionTimeout "[class search -all -value datagroup_selfridges_waitingroom starts_with "session_timeout"]"
}

If you want some/all of these lookups done more frequently, you could move them to the CLIENT_ACCEPTED event instead. Maybe the timeout and max_active_clients?

You can check if the cookie value isn't null in one step like this:

Current:

if {[HTTP::cookie exists $sessionCookieName]}{

set client_id [HTTP::cookie $sessionCookieName]`

Suggested:

if {[set client_id [HTTP::cookie $sessionCookieName]] ne ""}{

You can save a bit of CPU by using ne instead of != for text comparisons:

Current:

if { $sessiondata != "" } {

Suggested:

if { $sessiondata ne "" } {

Aaron

Just a thought (Aaron you may be able to advise on this one). With 20000 requests might the local logging be a factor in the CPU performance? Might it be better to log off box or implement HSL in the iRule instead?

 

Perhaps rem out the log local0 lines to see if this helps at all.

 

N

 

Thank Nathan/Hoolio. What is the method I turn off the logging just for this iRule? I will remove the log statements anyway.

 

Secondly customer wants the waiting room to be kicked in when a certain number of TCP connections is reached and not sessions. Is there a way to implement it with in this iRule?

 

Thanks in advance