BinaryLane does not provision servers with swap by default because, in our experience, the server's behaviour when using swap is worse(high disk I/O, server becomes unusable forcing power-cycle) than just having individual processes being killed to free up memory.
We don't expressly forbid people from creating their own swap files but as a general rule of thumb (of course there might be some exceptions) in the context of servers, if contents of memory have to be swapped out to disk on a routine basis it essentially means there's not enough RAM in the system.