HTTP Session Limit
Problem this snippet solves:
Limits total concurrent HTTP sessions to a pre-defined threshhold, allowing those clients with a session cookie to continue once the limit is reached, while redirecting new clients until concurrent sessions are again below the theshhold.
Code :
rule HTTP_session_limit {
when RULE_INIT {
set ::total_active_clients 0
set ::max_active_clients 100
log local0. "rule session_limit initialized: total/max: $::total_active_clients/$::max_active_clients"
}
when HTTP_REQUEST {
;# test cookie presence
if {[HTTP::cookie exists "ClientID"]} {
set need_cookie 0
set client_id [HTTP::cookie "ClientID"]
;# if cookie not present & connection limit not reached, set up client_id
} else {
if {$::total_active_clients < $::max_active_clients} {
set need_cookie 1
set client_id [format "%08d" [expr { int(100000000 * rand()) }]]
# Only count this request if it's the first on the TCP connection
if {[HTTP::request_num] == 1}{
incr ::total_active_clients
}
;# otherwise redirect
} else {
HTTP::redirect "http://sorry.domain.com/"
return
}
}
}
when HTTP_RESPONSE {
;# insert cookie if needed
if {$need_cookie == 1} {
HTTP::cookie insert name "ClientID" value $client_id path "/"
}
}
when CLIENT_CLOSED {
;# decrement current connection counter for this client_id
if {$::total_active_clients > 0} {
incr ::total_active_clients -1
}
}
}Published Mar 18, 2015
Version 1.0
brad_11480Nimbostratus
If the intention is to keep the connections to the pool of servers below a certain threshold, this would work. But I don't see how this would not end up interfering with an active application session if that user happens to return a transaction at a time that it was over the connection limit-- they may get a 'sorry' redirect in mid-session. For most web-based application sessions, it is a series of transactions where each transaction may be in a separate connection.
anatolyel_34600Hello . This one will work for a multiple domains?
- kridsana
Cirrocumulus
Hi @brad
From your comment, Is active session will get interfere ? because active session will have existing session cookie "ClientID" and then they will continue using application normally even though $::max_active_clients is reach .
I want to using this but still not sure if it will working.
- brad_11480
you are correct they have a ClientId cookie and will not drop a user. But this code seems to be more of a connection count limit and not a session count limit. A session spans multiple HTTP_REQUEST / HTTP_RESPONSE&CLIENT_CLOSED. Since it decrements the counter at close it makes it available for others even though this user still has a session active (a cookie active).
 
There are a couple other articles that I feel accomplish the session limit. I adapted one.. but look at: https://devcentral.f5.com/s/articles/codeshare-refresh-http-session-limit
 
- kridsana
I lookup irule in your comment. Why It's look like the same as this irule? (have same client_closed event with delete table = this irule decrement counter)
ps. I'll comment more in those link instead to not confusing.