[ upstream pipes in ]
                             /\      /\       /\ 
----firewall layer-   [FW1]    [FW2]    [FW3]    [FW4]  --scale me---->
                          \        \    /        /
                            ===== [switch] =====
                          /        /    \        \ 
----appserver layer-  [AS1]    [AS2]    [AS3]    [AS4]  --scale me---->
                          \        \    /        /
                            ===== [switch] =====
                          /        /    \        \ 
----memcached layer-  [MC1]    [MC2]    [MC3]    [MC4]
                        ||       ||       ||       ||   --scale me---->
----database layer-  +[DB1]----[DB2]----[DB3]----[DB4]+  
                     |_________failover ring__________|