LTM - load balancing to the same web server

Depending on the number of virtual hosts you're running, my initial reaction is that it might be more trouble than it's worth. The virtual hosts are merely front ends, right? So I don't really see one virtual host taking a dive when all the others are available, unless someone accidentally deletes the content.

Having said that, if you absolutely want that solution I would create one pool for each site with its' individual monitoring even though it is the same servers in all the pools. Then I would create an iRule that checks the Host header and sends the requests to the correct pool. That way you can do it with only one virtual server. Would that be useful?

That's my rational, seems a lot of work for no real gain.

So to clarify, create one virtual server with no attached pools, then create multiple pools with the same members and a monitor specific to that site. Then create an iRule to redirect the connection to a virtual server to a specific pool via the host header. Would have to lab it but seems logical - only thing is the virtual server would be down as it has no pool members, would have to lab it to see if it would work.

Thanks for the advice, really appreciated.

No worries, and no - the virtual server will not be down, it has a dependency on pool members available through iRules as well so it will all be good. Give me a holler if you need some suggestions about the iRule.

Just to add to Henrik's excellent idea:

when HTTP_REQUEST {    
    switch -glob [string tolower [HTTP::uri]] {        
        "/app1*" { pool app1_pool }            
        "/app2*" { pool app2_pool }            
    }        
}    

And then have a different pool and monitor(s) for each app. The beauty of this approach is that you scale up or down individual applications without affecting other services or modifying any code. If you wanted to get fancy with it, you could also do something like this:

if { [active_members app1_pool] < 1 } {    
    HTTP::respond 200 content "HTML maintenance page content"        
} else {    
    pool app1_pool        
}

Thanks Kevin, the first iRule saved me searching through Dev central.

The second one is really intriguing. I'm not sure how you add both rules, would you just add both iRules - the first one and a multiple of the second one per VS instance/page?. If that's the case the only concern is the number of iRules that would be added, sure there is a way to combine it all in one rule but that is above my scripting ability. Something to play with thou - thanks.

It's all a single iRule. The content in the second part would get inserted into the first and replace every pool statement.

No, the second part is an addition to the iRule. So the entire iRule would look something like this:

when HTTP_REQUEST {    
    switch -glob [string tolower [HTTP::uri]] {        
        "/app1*" {
            if { [active_members app1_pool] < 1 } {    
                HTTP::respond 200 content "HTML maintenance page content"        
            } else {    
                pool app1_pool        
            }
        }            
        "/app2*" {
            if { [active_members app2_pool] < 1 } {    
                HTTP::respond 200 content "HTML maintenance page content"        
            } else {    
                pool app2_pool        
            }
        }            
    }        
}    

Ahh, will give it a try when back at work. Thanks again.

Ahh, will give it a try when back at work. Thanks again.

Just showing off now ... Lol. Thanks guys, brilliant advice - all you advise will be used and appreciated.