Conditional Redirection

iRule on Source_Host VIP If Source_Host response is 404 then redirect to Target_Host.

can you try HTTP::respond instead of HTTP::redirect?

e.g.

root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm virtual bar
ltm virtual bar {
    destination 172.28.24.10:80
    ip-protocol tcp
    mask 255.255.255.255
    pool foo
    profiles {
        http { }
        tcp { }
    }
    rules {
        qux
    }
    source 0.0.0.0/0
    source-address-translation {
        type automap
    }
    vs-index 8
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm pool foo
ltm pool foo {
    members {
        200.200.200.101:80 {
            address 200.200.200.101
        }
    }
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm rule qux
ltm rule qux {
    when HTTP_REQUEST {
  if { [HTTP::host] eq "sourcehost.mydomain.com" } {
    set is_sourcehost 1
    set uri [HTTP::uri]
  } else {
    set is_sourcehost 0
  }
}
when HTTP_RESPONSE {
  if { $is_sourcehost and [HTTP::status] == 404 } {
    HTTP::respond 302 noserver Location "http://targethost.mydomain.com$uri"
  }
}
}

[root@centos1 ~] curl -i http://172.28.24.10/something -H "Host: sourcehost.mydomain.com"
HTTP/1.0 302 Found
Location: http://targethost.mydomain.com/something
Connection: Keep-Alive
Content-Length: 0