Techhawking

Last night I went to an SDForum talk by two eBay architects Randy Shoup and Dan Pritchett on how they built, scaled and run their operation. The talk didn’t have anything substantially different from what I’ve heard before, but was still impressive because they were applying some of the common thinking to their operations which runs over 15000 servers any given time. [ Slides ]
Here are a few interesting phrases I took away from the talk.

• Scale out not up: Scaling up is not only expensive, it will also become impossible beyond a certain technical limitation. Scaling out, however is cheaper and practical.
• Design to fail: Every QA team I know, do a whole batch of tests to make sure all components work as they should. Rarely have I seen a team which also does testing to see whether the servers stay up if certain parts of the application fail.
• If you can’t split it, you can’t scale it: Ebay realized early on that anything which cannot be split into smaller components can’t be scaled. A good example of such operation are the “joins” on multiple tables in a database. Relying on database to do joins across a large set of tables means that you can never partition those tables into different databases. And if you can’t split it, you will have t
• Virtualize components: If they can virtualize it, and create an abstraction layer to take care of these virtual components, then rest of the application need not worry about the actual server names, database names, table names etc. The Operations team can move components around to suite scalability needs.

This will be an interesting trend to follow. This linux+perl distribution is made up of just linux kernel and perl binaries. Rest of the tools are all written in perl shell scripts. Miguel de Icaza, the creator of mono is looking for folks to do the same with mono.

I think its a great experiment and will help validate mono as a practical alternative to other frameworks/languages on linux. But what will be even cooler (for me atleast) is if someone can create a true Object oriented shell experience like Microsoft’s powershell/monad. And incase you didn’t know, Powershell/Monad is the new shell by Microsoft using .net framework. It will probably replace cmd sometime in the future.
That being said, it doesn’t really have to be mono. Java is a perfect candidate for it as well. There was a java project related to a java based shell which I don’t think is active anymore… may be someone can revive it.

Can it be done ?

The same origin policy prevents document or script loaded from one origin from getting or setting properties (XMLHttpRequest) of a document from a different origin. The policy dates from Netscape Navigator 2.0. This is a very important security restriction which disables rogue third-party javascripts from getting information from your authenticated banking server session.

Unfortunately, this also almost completely shuts down any possibility of data sharing between multiple servers. Note the use of the word “almost”, because “JSON” is the new Saviour of web2.0 world. JSON or Javascript Object Notation, is nothing but a simple data interchange format which can be easily used by javascript applications. Whats different here is that unlike XMLHttpRequest which can send back answers in any format the javascript application wants, JSON requires the answers to be in JSON format, which is basically a subset of Javascript Programming language, or to be more specific Standard ECMA-262.

For those who are curious how this works and don’t have time to read the complete documentation, the difference is that a javascript application can still call other javascripts to be loaded from third party websites. So if you are running an application on www.royans.net and you have some data on data.royans.net, you can load that data into your application as long as you masquerade that information as a javascript.

Thats it, there is no rocket science here… but it does feel like one when you first come across it. I surely did.

While you are at it, watch out for JSONP (JSON with padding) too. Google is one company which I know have been using such mechanisms for a long time. They recently came out with more vocal support of this new open data interchange standard.
Oh, and before you go hacking your code, one thing you might like to watch out is to avoid opening up private/privileged information using JSON mechanism, because its open to XSS (Cross site scripting hole).

I’ve been using Firefox for a long time, and have always had Web developer plugin by my side for those miserable days. This tool which can save your ass at a time when you really need to understand what the heck your Ajax code is up to.

A couple of days ago I came across another such tool called  Firebug. All I have to say is that I was completely blown away by its intutive debugging style Cleaning up my messy Ajax generated code could have been a lot worse if this guy wasn’t around.
Here is a quick feature list

* JavaScript debugger for stepping through code one line at a time
* Status bar icon shows you when there is an error in a web page
* A console that shows errors from JavaScript and CSS
* Log messages from JavaScript in your web page to the console (bye bye “alert debugging”)
* An JavaScript command line (no more “javascript:” in the URL bar)
* Spy on XMLHttpRequest traffic
* Inspect HTML source, computed style, events, layout and the DOM

• I played around with two interesting javascript toolkits which help you make rounded-corners in your html pages without using images. Rico and Trancorners.
• DD-WRT is a opensourced kernel for Broadcom based wireless routers.
• During my work using CSS I found some interesing CSS tips and tricks sites.
• OpenSuse is finally here. Release Candidate 1 (RC1) of openSUSE 10.2 is codename Basilisk Lizard.
• 130 Ajax Tutorials
• Google is planning to add its blog search engine to its main google search website
• Zune didn’t have a USB drive mode, but now it been hacked