Category Archives: Server

A new server

So for the past couple months my server has been going on and off due to the fact that rackspace increased their retirements of swapping and such. I made the swap to Amazon EC2 today and so over the next couple weeks we’ll see how this works out.

256Mb doesn’t do what it used to…

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).

MMO Asteroids in Node.js…but for real.

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:

The MMO itself can be viewed here: 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.

Multiprocessing with the WebSocketServer

After spending way to much time thinking about exactly how to do it, I have got multiprocessing working with the WebSocketServer.

I have learned some interesting things about multiprocessing with Python:

  • Basically no complicated objects can be sent over queues.
  • Since pickle is used to send the objects, the object must also be serializable
  • Methods (i.e. callbacks) cannot be sent either
  • Processes can’t have new queues added after the initial creation since they aren’t picklable, so when the process is created, it has to be given its queues and that’s all the queues its ever going to get

So the new model for operation is as follows:

WebSocketServer Diagram

WebSocketServer Diagram

Sadly, because of the lack of ability to share methods between processes, there is a lot of polling going on here. A lot. The service has to poll its queues to see if any clients or packets have come in, the server has to poll all the client socket queues to see if anything came in from them and all the service queues to see if the services want to send anything to the clients, etc. I guess it was a sacrifice that had to be made to be able to use multiprocessing. The advantage gained now is that services have access to their own interpreter and so they aren’t all forced to share the same CPU. I would imagine this would improve performance with more intensive servers, but the bottleneck will still be with the actual sending and receiving to the clients since every client on the server still has to share the same thread.

So now, the plan to proceed is as follows:

  • Figure out a way to do a pre-forked server so that client polling can be done by more than one process
  • Extend the built in classes a bit to simplify service creation and to make it a bit more intuitive.

As always, the source is available at

Making a WebSocket server

For the past few weeks I have been experimenting a bit with HTML5 WebSockets. I don’t normally focus only on software when building something, but this has been an interesting project and has allowed me to learn a lot more about the nitty gritty of sockets and such. I have created a github repository for it (it’s my first time using git and I’m loving it) which is here:

The server I have runs on a port which is considered a dedicated port for WebSocket-based services. The server is written in python and defines a few base classes for implementing a service. The basic structure is as follows:

Super-basic flowchart

Each service has its own thread and inherits from a base class which is a thread plus a queue for accepting new clients. The clients are a socket object returned by socket.accept which are wrapped in a class that allows for communication to the socket via queues. The actual communication to sockets is managed by a separate thread that handles all the encoding and decoding to websocket frames. Since adding a client doesn’t produce much overhead, this structure potentially could be expanded very easily to handle many many clients.

A few things I plan on adding to the server eventually are:

  • Using processes instead of threads for the services. Due to the global interpreter lock, if this is run using CPython (which is what most people use as far as I know and also what comes installed by default on many systems) all the threads will be locked to use the same CPU since the python interpreter can’t be used by more than one thread at once (however, it can for processes). The difficult part of all this is that it is hard to pass actual objects between processes and I have to do some serious re-structuring for the code to work without needing to pass objects (such as sockets) to services.
  • Creating a better structure for web services (currently only two base classes are really available) including a generalized database binding that is thread safe so that a service could potentially split into many threads while not overwhelming the database connection.

Currently, the repository includes a demo chatroom service for which I should have the client side application done soon and uploaded. Currently it supports multiple chatrooms and multiple users, but there is no authentication really and there are a few features I would like to add (such as being able to see who is in the chatroom).

New Host!

Thanks to my friend Walter Zarnoch, I now have a hosting plan that will work for the next two years while I am gone on a mission for my church. The plan is to basically keep my site up here while I am gone, hopefully getting hits and such from people interested in the crap on here, and then work on it after I get back. As for the future, I might keep this arrangement, but for all I know I might find out about a better arrangement later. Right now we share a hosting plan, splitting the cost 50/50, so its really not too bad at all costwise for a site I won’t really be touching for two years.

Anyway, hopefully this works out…and I am sure glad to be off my grandma’s website’s host.

Not so temporary…

Well I have decided to place my actual website on this server. My home server has failed due to router issues and I will probably be redesigning the entire website in the near future anyway since it uses outdated layout techniques. This server is basically the website that I work on for my dad’s side of the family. I plan on downloading the contents of my server to here over the weekend so that I can try to clean things up a bit and hopefully get this site back on the map.

I will probably post progress on the new smith-marsden site here since that is currently my main development challenge.

Additional features of the new smith-marsden site:

  • Ability to invite other users given to everyone
  • RSS feeds on letter submissions
  • More information stored so that it is all in one place that is private rather than facebook or somethwere else which could be quite public
  • New state of the art layout techniques enhance the website
  • AJAX allows pages to submit forms without reloading, making page load times faster and looks really cool.
  • The entire thing is made using CakePHP, a robust framework.
  • More to come as I think of them and make them…