A load balancer written in DALIS

I mentioned to a friend of mine that I wanted to slap together a quick load balancer to demonstrate that DALIS programs can bounce between different servers without the need for any shared state. Being able to do that was my original aim for writing a cloud based language, and a demo showing DALIS in action would be nice to have. Of course, I had intended to simply extend my C# webserver example and make a simple load-balancer out of that. But my friend happened to say “why don’t you write the load balancer in DALIS?”. Damn him, putting ideas in my head like that. Still I got my own back when I showed him the Esoteric Programming Languages site and he spent way too much time reading it :-) So ... here is my (very simple) load balancer written in DALIS:

TRANSPARENT
IF ISASSIGNED("arg0")
   IF (RANDOM >= 0.5)
      newUrl = REPLACE arg0, "DALIS", "DALIS1"
   OTHERWISE
      newUrl = REPLACE arg0, "DALIS", "DALIS2"
   END
   IF ISASSIGNED("arg1")
      newUrl = REPLACE newUrl, "balance", arg1
   END
   IF RAWCONTENT = ""
      WRITE WEBGET newUrl
   OTHERWISE
      WRITE WEBPOST newUrl, RAWCONTENT
   END
END

I had to add a few new things to the language to make this work (it is great when you’re the boss of the programming language and you can add whatever you like):

  • RANDOM – generate a pseudo random number between 0.0 and 1.0
  • RAWCONTENT – allows your program to access the data in the raw http request
  • TRANSPARENT – tells DALIS that you don’t want it to add anything to the output
  • WEBPOST – does an http POST with the data you specify
  • REPLACE – replace a value in some text with some new value

Anyway, this seems to work a treat, it means that you can run 3 separate DALIS servers (called DALIS, DALIS1 and DALIS2 in this example), one being the load-balancer, along with two others. You can then run a DALIS program via the load-balancer and it will route it randomly to one of the other two DALIS servers. Using the TRANSPARENT keyword in the load-balancer code is critical, since it allows stuff to simply pass through without any interference.

The trouble is, I’m actually starting to enjoy programming in DALIS now. What have I done?