Distributed Applications

I read an article by Cory Doctorow in volume 26 of Make Magazine about two interrelated topics: distributed denial of service (DDoS) attacks, and the difficulty of finding a willing hosting provider for your site when it comes under scrutiny from and legal pressure by government agencies seeking information and data by force. In each case, your site, or one upon which you rely, can be slowed or stopped, either by a person or group who apply brute-force technology (whether governmental or otherwise), or by the equally overwhelming force of law. The result in either case is a chilling effect upon the willingness of hosting providers to host your site once it becomes more trouble than it is worth.

It got me thinking about what might be done to prevent or frustrate such attacks; is there a way to distribute not only the network itself, but the applications that run on it as well? Server farms and load balancers don't go far enough because they still concentrate application resources at one provider, even if they have multiple locations, backups, alternate internet backbones, and all the rest of the safeguards that go toward giving them the ability to guarantee uptime.

What comes to mind is a protocol like BitTorrent where resources are distributed not in a client-server way but in a peer-to-peer topology, providing redundancy and distribution of data in a way that would be much more difficult to stop or interrogate than the traditional internet server model. Imagine a DDoS attempt on a BitTorrent "hosted" application: there is no single choke point to attack. What about a subpoena requesting hosting information when the peer hosts are so varied in number and location?

Of course there is a major flaw in this simplistic approach: how do you trust the peers who are hosting part of your application not to poison the torrent, examine incoming and outgoing traffic, etc? Also, the nature of applications today is that they are interactive and real-time, not "download once and run," and even if you did choose to use application logic that lives solely on the client once it is obtained, in most cases in order to be useful at all the application will need to communicate with network resources and possibly persist data in the cloud.

But, in terms just of redundancy, distribution, and the lack of a central hosting provider, that kind of model seems like a step in the right direction.

Unresponsive Mac Mini at login or blue screen

I just resolved a very long-standing problem with our Mac Mini that has been dogging me ever since upgrading to Snow Leopard. The problem was that the machine would stick on the blue screen when logging off one user and before displaying the login screen. Then, even after displaying the login screen mouse clicks were unresponsive, although the mouse pointer still moved in response to user input.

I tried a lot of fixes, some expensive:

1) Install new RAM, taking it from 1gb to 4gb
2) Install a larger hard disk drive, taking it from 120gb to 320gb (now using the 120 on a Linux machine and it reports as being perfectly healthy, as it did within OSX)
3) Added the entire HDD to the "privacy" list in Spotlight to prevent indexing of the entire disk
4) Disabled indexing from the command line (and did not turn it back on)
5) Ran Disk Utility | Repair Disk Permissions

All of those are things that various posters in various forums suggested as a fix to what sounded like the same or very similar problems, but none of them worked. Finally I had an idea to search on terms related to the login screen and fast user switching rather than things like "slow," "unresponsive," and the like. Something I saw caught my eye relating to fast user switching and a difference in the way the Accounts utility presents the options for fast user switching between newer versions of OSX and older ones. Most interesting is the fact that we were not using fast user switching; if I was logged in and my wife wanted to use the computer, I had to log out and then she could log in. I think at one point I may intentionally have disabled fast user switching, thinking that it was a way to conserve system resources and therefore improve performance.

It turns out that with Snow Leopard you don't so much get to choose between *whether* to use fast user switching and single-user-only mode, you just get to choose *how* OSX goes about it by choosing an option in the "Show fast user switching menu as:" dropdown list, which has a checkbox next to it that controls whether you actually use fast user switching. On our machine that option was unchecked, so I checked it and left the default option of "Name" in the list. Here's what it looks like in the Accounts screen:

The difference is like night and day: no more lag, no more wondering if the screen ever will come back, it just works. So far I have tested by locking my screen, logging in as a different user, locking that screen, switching back to my screen, and other tests like that. I also have logged completely off a user and back on as an already logged-on user, and a couple of other combinations that fit the pattern of our normal, regular usage of the machine, and they all still work. What I haven't tried yet (because I wanted to post this blog entry and not risk being unable to log back in immediately) is powering the computer all the way down and turning it back on, which also exhibited the same frustrating behavior.

At the moment I'm not feeling brave enough to test the negative by unchecking the box to see if the behavior returns, but that's my hypothesis. Looking at things from a black box perspective, it would seem that there is some kind of hangup within OSX where it lags like crazy when switching users if you are in Snow Leopard and if you have unchecked the "Show fast user switching menu as:" checkbox. Rather than letting the user check the checkbox that causes all the trouble and does not otherwise seem to control any option, perhaps that checkbox should just go away.

If you are having the horribly frustrating behavior like we were having and have tried everything else to no avail, take a look at your Accounts settings and see if the fast user switching checkbox is unchecked; it's about as simple a solution as you can get to an incredibly frustrating problem, it's just not at all obvious or even intuitive how to go about finding the fix.

Fun at the dentist

Against my better judgment I told my dentist today that I have a tooth that hurts if I chomp down on something crunchy like hard candy; her reaction to that is to have me bite down on a hard, plastic dental tool thing, which of course hurts like a mother. Is that to see if I am lying?

Just to make doubly sure she targeted the problem tooth a second time, sort of like on those personality profile tests where you get the same question multiple times to see if you contradict yourself. Yep, still hurts when I do that!

Arduino vs. Netduino, or How Netduino totally misses the point

I am a developer both professionally and as a hobbyist; I can't get enough of the stuff. One of the things I really like to do after a hard day of slinging code that, if I'm honest, is just slightly less than sexy, is cobble together some real-life hardware components, and then write the code to make them do cool things like read light values, power motors, and make noise with synthesizers. It's a nice change to do hands-on work and I find it enjoyable and relaxing. In other words, I write business apps by day, so I like to play hardware at night.

The hardware I am speaking of is Arduino, an open source hardware and software platform that has tons of libraries, users, and documentation. The development environment is intentionally limiting, and when compared to something like Visual Studio .NET where I do my day-to-day work, it is refreshing in its simplicity. It is actually not very good at all when compared with VS.NET, but it's not meant to be anywhere near the same thing. In its favor is the fact that I am able to use it from any computer in the house, even though that means multiple versions of Windows, a couple of Linux machines, and even a Mac mini.

But, many times over the past couple of years that I have been tinkering with Arduino I found myself wishing that I could write code in the language that dominates most of the work I do: C#. Arduino uses C++, which is at least a familiar syntax, but when you've been used to working with C# and the .NET framework, it's a bit of a pain to go back to the bad old days of C/C++.

So, a little while back I started hearing about Netduino, which is like Arduino in terms of being an open source hardware/software platform, but which uses C# and .NET as its development environment and framework instead of C/C++. Very recently I decided to check it out, thinking that this must be a marriage made in heaven: my favorite development environment combined with really cool hardware hacking; what could be better?

Well, here's the rub: Netduino totally misses the point of Arduino. The hardware is open source, sure, but who in their right mind is going to brave soldering surface-mount 100 pin chips (the Netduino processors)? Who really wants an ARM chip for a microcontroller, even if it would be cool to have built-in USB, LAN, and all the other stuff that the Netduino chips have? The whole point, to me, is simplicity, and the fact that even with my earthquake-shaky hands I still can manage to solder a simple 28-pin chip to a prototype board. Sure, the thing has hardly any memory at all, and no built in USB or LAN, but that's what gives it its charm: I can make really fun little learning projects with blinky LEDs and inputs that read analog potentiometers, and I don't expect it to have more technology in it than a damn cell phone.

I downloaded, but have not yet installed, the Netduino development kit, so I still have hope that I can ditch the fancy ARM chip and use the trusty old Atmega168, but I am expecting to be disappointed.

Here's hoping that I am wrong.

Lego store augmented reality display

Saw the coolest thing the other day at a Lego store: they have a video display with a video camera where you hold up a product box for one of the toy kits they sell, and the camera figures out which kit it is and then displays a 3D, animated sequence that appears on the display to be *on* the box you are holding in your hands.

Lego Store Augmented Reality Display

You can change the position of the box to see the display from various sides and angles, which is very cool.

I was curious to know whether there was some sort of RFID magic going on for the initial image recognition, so I took a picture with my iPhone and then held up the resulting image to the Lego display's video camera to see if the software still would recognize the Lego kit package and run the animation. I was impressed to see that not only did it work, but it was scaled down in size relative to the size of the image on the iPhone's display! The shiny finish of the iPhone display would reflect the bright store lights into the display's camera at certain angles and overpower it, killing the animation, but still, that was pretty cool.

Unintentional (I hope) humor in pithy church sign message 'o the day

There's a church I pass on the way to work each day that has one of those sliding-letter message boards with a trite saying on it that is meant to convey some humorous, God-related wisdom that always makes me smile.

Today's sign reads:

download your worries
get online with god

Shouldn't that be "upload" your worries?

Awesome circuit diagram at XKCD