Forum Discussion

Mike_S_59924's avatar
Mike_S_59924
Icon for Nimbostratus rankNimbostratus
Nov 15, 2008

dealing w/ heavy load via try again later site

We would like to setup up two nodes in a pool as follows.

 

All traffic goes to node 1 until there there are 500 connections.

 

After that traffic goes to node 2 which is a site that just says try again later.

 

Once a user gets to node 1, we want them to stay there.

 

Once node 1 clears up a bit, new users get back to node 1.

 

 

This is a legacy site and load balancing is not an option. It is running a black box piece of software so getting into its bowels and having it tell uers to come back later is not an option either.

 

 

Thanks in advance.

 

 

application delivery
dev
devops
iRules
  • hwidjaja_37598's avatar
    hwidjaja_37598
    Icon for Altostratus rankAltostratus
    Nov 17, 2008
    Try this: 

     
 when RULE_INIT { 
 set ::MaxConn 500 
 set ::CurConn 0 
 set ::RejectList [list / .html .htm .asp .pl ] 
 } 
  
 when CLIENT_ACCEPTED { 
 incr ::CurConn 
 } 
  
 when CLIENT_CLOSED { 
 incr ::CurConn -1 
 } 
  
 when HTTP_REQUEST { 
 if {  
 ($::CurConn > $::MaxConn) and \ 
 ([matchclass [HTTP::path] ends_with $::RejectList]) \ 
 } { 
  
 HTTP::respond 200 content " 
  
 Please Try again later 
  
 Please Try again later 
  
  
 " 
 drop 
 }  
 }

    The iRule will only block html document and still allow non-html document (eg. image/flash/video).

    It's using global variable which means it doesn't work perfectly in CMP platform (1600, 3600, 8400, 8800 and Viprion). As a 'workaround', you divide MaxConn with number of tmm process in yous system (eg. ps | grep npus). Statistic Profile might be better in CMP platform.

    Modify it according to your environment.
  • Mike_S_59924's avatar
    Mike_S_59924
    Icon for Nimbostratus rankNimbostratus
    Nov 17, 2008
    Thanks Humphrey, this is great. I'm sure the user is going to ask about a better "come back late page, branded w/ the graphics of the site, etc." Is there a way to redirect to another node?

     

     

    Also what defines a connection vs. a session. They will get grumpy if users already in get redirected. My experience on the Microsoft IIS side is connections even SSL break pretty regularly and are re-established within a user "session". Is that the same for connections at the LTM level?

     

     

    Sorry for the follow-up questions.