Electronics, Embedded Systems, and Software are my breakfast, lunch, and dinner.
So, this last week I got an email from rackspace saying that my server was thrashing the hard drives and lowering performance of everyone else on that same machine. In consequence, they had rebooted my server for me.
I made a few mistakes in the setup of this first iteration of my server: I didn't restart it after kernel updates, I ran folding@home on it while running nodejs, and I didn't have backups turned on. I had it running for well over 200 days without a reboot while there had been a dozen or so kernel updates. When they hard rebooted my server, it wouldn't respond at all to pings, ssh, or otherwise. In fact, it behaved like the firewalls were shut (hanging on the "waiting" step rather than saying "connection refused"). I ended up having to go into their handy rescue mode and copy out all the files. I only copied my www directory and the mysql binary table files, but as you can see, I was able to restore the server from those.
This gave me an excellent opportunity to actually set up my server correctly. I no longer have to be root to edit my website files (yay!), I have virtual hosts set up in a fashion that makes sense and actually works, and overall performance seems to be improved. From now on, I will be doing the updates less frequently and when I do I will be rebooting the machine. That should fix the problem with breaking everything if a hard reboot happens.
I do pay for the hosting for this, 1.5 cents per hour per 256Mb of RAM with extra for bandwidth. I only have 256Mb and since I don't make any profit off this server whatsoever at the moment, I plan on keeping it that way for now. Considering that back in the day, 256Mb was a ton of memory, it clearly no longer suffices for running too much on my server (httpd + mysql + nodejs + folding@home = crash and burn).
Many people saw this april fools joke where the author said that he had created an asteroids MMO using Node.js. In reality, it was completely client side and was a bunch of bots. However, I did find the whole thing rather intriguing and decided to see what I could do with Node.js along this line. Last week I started on the project and this weekend I made enough progress that I can publish v0.0.1. It leaves several things to be desired, including a better game background so that one can tell when the view is shifting and user tracking so that you accumulate your scores over time. It does work and from what I can see its not horribly bad performance. While it certainly won't be able to handle thousands of clients, I expect that it should be able to handle somewhere between 50-100 before it starts dying. At the moment, its quite limited by the memory on my server and the client side scripting gives the impression of "stuttering" with the dead reckoning system used to make the animations smooth. The stuttering is caused by the linear and angular damping that I have running on the server side not being factored into the projected location on the client side.
For physics I am using Box2Dweb in a Node.js module which may be overkill, but its the simplest Javascript physics engine I could find since I didn't feel like writing my own. The server keeps track of all of the entities in the game and each client requests a "view" of an area of the room. The client is informed which player is them, but other than that it just sees all players and entities in the same list. The actual rendering function draws the entities onto the canvas dependent upon the type of the object.
I have made the source available on github here: https://github.com/kcuzner/mmo-asteroids
The MMO itself can be viewed here: http://kevincuzner.com:8080/. Note that at times it may be down since I am messing with my firewall right now and I might accidentally close the port. Just leave me a note in the comments and I'll try to get it working.