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Paul_Gaynor_706's avatar
Paul_Gaynor_706
Icon for Nimbostratus rankNimbostratus
Jan 16, 2009

IRule causes Virtual Servers to be "up"?

Hi Everyone,

When I replace the first iRule below with the second iRule belown on a virtual server the VS is marked up when the server pool has no available members? Any idea what might be going on here?

First iRule 

 
 when HTTP_REQUEST { 
   set uri [string tolower [HTTP::uri]] 
   if {$uri starts_with "/services"} 
    {} 
   else 
    { 
    HTTP::redirect https://[HTTP::host][HTTP::uri] 
    } 
 }

Replacement iRule 

 
 when HTTP_REQUEST { 
 if { [string tolower [HTTP::uri]] starts_with "/services" } { 
 pool ws_server_pool 
 } 
 elseif { [string tolower [HTTP::uri]] equals "/public/diagnostic.do"} 
 { 
 pool gs_server_pool 
 } 
 else { 
 HTTP::redirect https://[HTTP::host][HTTP::uri] 
 } 
 }

Thanks!

Paul
application delivery
dev
devops
iRules
  • wolfpack_98881's avatar
    wolfpack_98881
    Icon for Nimbostratus rankNimbostratus
    Jan 16, 2009
    I believe that the virtual will inherit any monitoring state of a pool referenced in an iRule. Your previous rule didn't contain a pool - thus it had no monitoring associated with it. Your new rule references 2 pools. It would only take 1 pool member among both pools to make the virtual "up". You can test this by marking all pools down and looking at the corresponding virtual status. I seem to also remember that if there are no monitors on the pools referenced within the irule - then the virtual where that irule applied with always be up. I'd personally love some confirmation on that, but that is at least the behavior that I've observed.
  • Nicolas_Menant's avatar
    Nicolas_Menant
    Icon for Employee rankEmployee
    Jan 16, 2009
    i confirm what wolfpack said. Status of pool within the iRule will impact the VS status.
  • Paul_Gaynor_706's avatar
    Paul_Gaynor_706
    Icon for Nimbostratus rankNimbostratus
    Jan 16, 2009
    Yeah, i verified that taking down the nodes in the pools that are referenced in the iRule does change the status of the VS.

     

     

    Is this good behavior?

     

     

    I would expect the primary pool as a resource of the VS to be the determining factor for the VS being up/down or the requirement that all referenced pools in the iRules have to be available for the VS to be available, not just one pool.

     

     

    I have verified that a GTM which monitors the LTM still sees the servers as unavailable even though the LTM has the VSs marked as up.

     

     

    Thanks for the replies

     

    -Paul
  • dennypayne's avatar
    dennypayne
    Icon for Employee rankEmployee
    Jan 21, 2009
    I have found a "trick" to get around this behavior. If you set the pool name as a variable and then call the variable in the pool statement, the iRule doesn't seem to "know" about status anymore. I had a similar problem with this rule: 

     
 when HTTP_REQUEST { 
  If the QA cookie exists, go to the QA pool. 
 if { [HTTP::cookie exists "QAPilot"] } { 
 pool WWW-QA 
 } 
 else 
 { 
 pool WWW-GLOB 
 } 
 } 
 when LB_FAILED { 
     LB::reselect pool WWW-GLOB 
 }

    However, we needed the VS to fail if WWW-GLOB was down, even if WWW-QA was up (due to OSPF route advertisement). Doing this fixed the problem (since WWW-GLOB was set as the default pool, if the "if" doesn't fire it will fall out to that): 

     
 when HTTP_REQUEST { 
  If the QA cookie exists, go to the QA pool. 
 if { [HTTP::cookie exists "QAPilot"] } { 
 set lb_pool "WWW-QA" 
 } 
 else 
 { 
 set lb_pool "WWW-GLOB" 
 } 
 pool $lb_pool 
 } 
  
  If load balancing fails to the QA pool, load balance to the PROD pool. 
 when LB_FAILED { 
     LB::reselect pool WWW-GLOB 
 }

    Denny