iRule for maintenance page

when CLIENT_ACCEPTED {
   set dpool [LB::server pool] }

when HTTP_REQUEST {
   if { [active_members pool $dpool] < 1 } {
      HTTP::redirect "http://maintenancepage.html" }
 }

You could technically evaluate the default pool directly in the HTTP_REQUEST event:

if { [active_members [LB::server pool]] < 1 } {
    [do something]
}

But you'll likely find the difference in memory footprint negligible.

I need an inline (no HTTP redirect) long maintenance page for a particular website, and I want to get around the bug in "LB_FAILED" (ID 222034). Below is a cut-down version of my code:

when HTTP_REQUEST {
    switch -- [string tolower [HTTP::host]] {
        "www.example.com" {
            pool www.example.com_pool
            set selected_server [LB::server addr]
            if {$selected_server == ""} {
                 If there are no members available, generate a long Maintenance Page
                HTTP::respond ...
            }
        }
        "www.example2.com" {
            pool www.example2.com_pool
            ...
        }
    }
}

Will anybody comment on whether this will work, or if there is anything not right here, or if there is a better way to achieve the same effect?

I think a better way would be to do a check if there are pool members before you select the pool. I would look at the example:

when HTTP_REQUEST {
switch -- [string tolower [HTTP::host]] {
"www.example.com" {
    if { [active_members www.example2.com_pool] < 1 } {
         If there are no members available, generate a long Maintenance Page
        HTTP::respond ...
    } else {
    pool www.example.com_pool
}
"www.example2.com" {
    pool www.example2.com_pool
    ...
    }
}

}

Hopefully this will get you started to getting this working

How do I create an iRule on the GTM that redirects to a maintenance page, if all Virtual Servers in a pool are not available?

Understand of course that GTM does DNS, and you're looking for an HTTP redirect. Two different things. You can certainly create an LTM iRule to redirect to a maintenance page if pool members are down. But a DNS request isn't going to produce an HTTP response.

Thanks Kevin for your response. How about a maintenance page in case both virtual servers are available in a Wide IP pool? This particular application has to be in an active standby state. If one of the virtual servers are not available I can setup the maintenance page at the LTM level. I also want a maintenance page in case both virtual servers are available in a WIP pool.