How to build the Web

Slide 1: How to build the Web Simon Willison 30th November 2007

Slide 2: This talk • Modern client-side engineering • Server-side engineering and web frameworks • Web application security • Building sites that scale

Slide 3: What to build How to build it Product design Browsers! Information architecture Client-side engineering User experience Social software design Servers! Usability Server-side engineering Marketing ...

Slide 4: Client-side engineering

Slide 5: The great myth of client-side development “It’s way easier than server-side development - after all, it’s just HTML”

Slide 6: That’s hogwash

Slide 7: “Yahoo! Juku is a comprehensive, 3-6 month program to train professional front end developers. The curriculum includes advanced topics in JavaScript, DOM, HTML, CSS,YUI, performance, and accessibility. Why train raw recruits to this degree? Well, in the San Francisco Bay Area, including the Silicon Valley, it’s hard-as-heck to find good front end programmers and web designers.” http://developer.yahoo.net/blog/archives/2007/11/the_harvard_of.html

Slide 8: Quines char*f=\"char*f=%c%s%c;main() {printf(f,34,f,34,10);}%c\"; main(){printf(f,34,f,34,10);}

Slide 9: (*O/*_/ http://ideology.com.au/polyglot/ Cu #%* )pop mark/CuG 4 def/# 2 def%%%%@@P[TX---P\\P_SXPY!Ex(mx2ex(\"SX!Ex4P)Ex= CuG #%* *+Ex= CuG #%*------------------------------------------------------------------*+Ex= Polyglots CuG #%* POLYGLOT - a program in eight languages 15 February 1991 *+Ex= CuG #%* 10th Anniversary Edition 1 December 2001 *+Ex= CuG #%* Written by Kevin Bungard, Peter Lisle, and Chris Tham *+Ex= CuG #%*------------------------------------------------------------------*QuZ= CuG #%* *+Ex= CuG #%*!Mx)ExQX5ZZ5SSP5n*5X!)Ex+ExPQXH,B+ExP[-9A-9B(g?(gA'UTTER_XYZZXX!X *+ CuG #(* *( C # */); /*( C # *) program polyglot (output); (*+ C # identification division. C C # program-id. polyglot. C # C # data division. Perl C # procedure division. C # Pascal C # * ))cleartomark /Bookman-Demi findfont 36 scalefont setfont ( C #* ( C # Fortran C #* hello polyglots$ C # main. COBOL C # perform C /# * ) 2>_$$; echo \"hello polyglots\"; rm _$$; exit; C #*( PostScript C # C *0 ) unless print \"hello polyglots\\n\"; __END__ bash/sh/csh print C stop run. -*, 'hello polyglots' x86 assembler C C print. C display \"hello polyglots\". ( C */ int i; /* C */ main () { /* C */ i=printf (\"hello polyglots\\n\"); O= &i; return *O; /* C *) (* C *) begin (* C *) writeln ('hello polyglots'); (* C *) (* ) C * ) pop 60 360 ( C * ) pop moveto (hello polyglots) show ( C * ) pop showpage (( C *) end .(* ) C)pop% program polyglot. *){*/}

Slide 10: Rendering engines

Slide 11: Rendering engines Opera desktop Safari Opera mobile iPhone Nintendo Wii Nokia Series 60 Nintendo DS Google Android Firefox Ice weasel Sadly still 85% Camino of the market Galleon

Slide 12: IE is the problem child • Microsoft simply stopped updating it once they had won the browser wars... IE 6 came out in 2001! • Still has shaky support for CSS 2.1 • Many JavaScript APIs developed before standards even existed • Requires a disproportionate amount of development time • Status of IE 8 is uncertain

Slide 13: Recommendations • Develop to the standards using Firefox • The cases where IE deviates from the standards are relatively well understood, and can usually be worked around • Avoid CSS hacks; conditional comments are your friend <!--[if IE]><link rel=\"stylesheet\" type=\"text/ css\" href=\"/static/ieonly.css\"><![endif]-->

Slide 16: Accessibility • Assistive technology thrives on semantic HTML • <label> elements for forms • <h1>...<h6> headers for structure • Avoiding tables for layout • Watch a video of a screen reader user; they may well browse faster than you do • Accessibility is much more than just screen readers - colour blindness, motor disorders, learning disabilities, even just poor eyesite

Slide 17: JavaScript “JavaScript was a rushed little hack for Netscape 2 that was then frozen prematurely during the browser wars, and evolved significantly only once by ECMA. So its early flaws were never fixed, and worse, no virtuous cycle of fine-grained community feedback [...] ever occurred.” -Brendan Eich

Slide 18: But despite that... • JavaScript is actually a really neat little language • Functions are first-class objects • Lexical closures • Objects are hash tables • If you take the time to learn it, it will repay you handsomely

Slide 20: Ajax

Slide 21: February 2005

Slide 22: AJAX v.s. Ajax “Asynchronous JavaScript + XML”

Slide 23: AJAX v.s. Ajax “Any technique that “Asynchronous allows the client to JavaScript + XML” retrieve more data from the server without reloading the whole page”

Slide 24: Unobtrusive JavaScript • JavaScript isn't always available • Security conscious organisations (and users) sometimes disable it • Some devices may not support it (mobile phones for example) • Assistive technologies (screen readers) may not play well with it • Search engine crawlers won't execute it • Unobtrusive: stuff still works without it!

Slide 25: Progressive enhancement • Start with solid markup • Use CSS to make it look good • Use JavaScript to enhance the usability of the page • The content remains accessible no matter what

Slide 26: Unobtrusive examples

Slide 27: labels.js • One of the earliest examples of this technique, created by Aaron Boodman (now of Greasemonkey and Google Gears fame)

Slide 30: How it works <label for=\"search\">Search</label> <input type=\"text\" id=\"search\" name=\"q\"> • Once the page has loaded, the JavaScript: • Finds any label elements linked to a text field • Moves their text in to the associated text field • Removes them from the DOM • Sets up the event handlers to remove the descriptive text when the field is focused • Clean, simple, reusable

Slide 31: easytoggle.js • An unobtrusive technique for revealing panels when links are clicked <ul> <li><a href=\"#panel1\" class=\"toggle\">Panel 1</a></li> <li><a href=\"#panel2\" class=\"toggle\">Panel 2</a></li> <li><a href=\"#panel3\" class=\"toggle\">Panel 3</a></li> </ul> <div id=\"panel1\">...</div> <div id=\"panel2\">...</div> <div id=\"panel3\">...</div>

Slide 34: How it works • When the page has loaded... • Find all links with class=\"toggle\" that reference an internal anchor • Collect the elements that are referenced by those anchors • Hide all but the first • Set up event handlers to reveal different panels when a link is clicked • Without JavaScript, links still jump to the right point

Slide 35: Django filter lists • Large multi-select boxes aren't much fun • Painful to scroll through • Easy to lose track of what you have selected • Django's admin interface uses unobtrusive JavaScript to improve the usability here

Slide 38: • Ajax is often used to avoid page refreshes • So... • Write an app that uses full page refreshes • Use unobtrusive JS to \"hijack\" links and form buttons and use Ajax instead • Jeremy Keith coined the term \"Hijax\" to describe this

Slide 39: JavaScript libraries “The bad news: JavaScript is broken. The good news: It can be fixed with more JavaScript!” - Geek folk saying

Slide 40: Main contenders • Prototype • The Yahoo! User Interface Library • The Dojo Toolkit • jQuery • It’s worth evaluating these in detail, but if you only have time to learn one...

Slide 41: The short answer: use jQuery

Slide 42: Client-side performance • Relatively new field, pioneered by the performance team at Yahoo! • A few simple changes can make a huge difference to perceived loading times • Example tip: serve your static files (CSS, images etc) from a separate domain - that way the cookies from your regular domain won’t slow down the requests

Slide 44: Server-side engineering

Slide 45: URL design (Yes, I should probably be calling them URIs)

Slide 46: Bad URLs example.com/index.html example.com/article.php?sectionId=2343&contentId=638 example.com/blog/2007/December.aspx www.amazon.com/dp/0596516177? tag=davidflanagancom&camp=14573&creative=327641&linkCode=as1& creativeASIN=0596516177&adid=165MWWERY4H71AJERGNZ& • Unnecessary filenames • Expose implementation details • Overly complex

Slide 47: Characteristics of good URLs • “Cool URIs don’t change” • Guessable • Hackable • Readable over the phone • Reflects the hierarchy of the site and its data

Slide 48: A good URL • simonwillison.net/2007/Nov/27/thumbnail/ • Short, hackable, no implementation exposed • No matter what you’re building, including the year can be really useful in allowing you to change your opinion on your URLs later on without breaking old links

Slide 49: The Open Source stack • The only option I would consider • Open source means: • Zero vendor lock-in; many open-source components are interchangeable • Better support (fix it yourself, or pay someone smart to fix it for you) • Less bugs and better quality code

Slide 50: Dynamic languages http://xkcd.com/303/

Slide 51: Dynamic languages • Social applications in particular are almost impossible to get right first time • Development only really starts after you’ve launched something and seen what people use it for • Speed and flexibility of development are critical • Dynamic languages let you get more done with less lines of code (which means less bugs)

Slide 52: LAMP • Linux • Apache • MySQL • PHP/Perl/Python

Slide 53: LAMP, evolved • Linux / FreeBSD / Solaris • Apache / Lighttpd / nginx / ... • MySQL / PostgreSQL • PHP/Perl/Python / Ruby

Slide 54: Web frameworks • Ruby: Ruby on Rails • Python: Django, Pylons, TurboGears • PHP: Symfony, CakePHP, Zend Framework • Perl: Catalyst, Maypole

Slide 55: Web frameworks • Ruby: Ruby on Rails • Python: Django, Pylons, TurboGears • PHP: Symfony, CakePHP, Zend Framework • Perl: Catalyst, Maypole

Slide 56: Django

Slide 57: Lawrence, Kansas - 2003

Slide 59: • Two developers • Two designers • Around a dozen editorial staff

Slide 74: How do you build a site like lawrence.com? • Interns - unpaid labour! • A big relational database • Newspaper people are baffled by these... • ... so you need a good interface for it • And as many development shortcuts as possible

Slide 75: Characteristics • Clean URLs • Loosely coupled components • Designer-friendly templates • Less code • The “good bits” from PHP

Slide 76: The Django stack • HTTP handling • Models (an ORM) • Views • Templates • Extras • Admin, RSS framework, generic views...

Slide 77: The Django workflow • Build the models • Instant admin! Content people can start adding data • Writing the views • Throw the templates to the designers

Slide 79: Open source Django • Django has been open-source since mid-2005 • The newspaper has been able to hire excellent developers from the community • The newspaper CMS is sold as Ellington; one of the features is that you can hire your own Django developers to modify it • Django has been hugely improved by contributions from outside the newspaper

Slide 80: www.djangosites.org

Slide 81: www.djangoproject.com

Slide 83: Don’t Repeat Yourself

Slide 84: All frameworks provide: • A recommended way of laying out code • Separation of application and presentation logic using a template system • An ORM, to reduce the amount of code needed to talk to a database • Reusable components for common tasks

Slide 85: Security

Slide 86: Three key attacks • SQL injection • XSS (cross-site scripting) • CSRF (cross-site request forgery)

Slide 87: SQL injection

Slide 88: • SQL injection is inexcusable • If the environment you are using doesn’t protect against this for you (through parameterised queries), use a different tool

Slide 89: Cross-site scripting • The most common security hole on the web http://example.com/search?q=<script>alert(\"hello\");</script> You searched for <?php echo $_GET['q']; ?> • Massive security hole!

Slide 90: XSS attackers can... • Replace your logo with something obscene • Steal your user’s authentication cookies • Re-target login forms to point to a password stealing script • Perform any action that the user is allowed to perform themselves • Create self-propagating worms

Slide 91: http://namb.la/popular/ http://namb.la/popular/tech.html samy is my hero

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Slide 93: HTML is dangerous • It’s best not to allow un-trusted users to submit HTML at all • If you let them submit HTML, you’ll need an industrial grade HTML parser (which emulates browsers, not just the HTML spec) and a very restrictive whitelist • CSS can include JavaScript, and even regular CSS positioning can be used for phishing

Slide 94: CSRF • Much less widely understood than XSS... • ... but almost certainly more common • Cross-site request forgery attacks allow attackers to force your users to take actions on your site that they didn’t mean to take • <img src=\"http://example.com/admin/delete.php?id=5\"> • Not just GET; hidden forms allow POST as well

Slide 95: <iframe style=\"width: 0px; height: 0px; visibility: hidden\" name=\"hidden\"></iframe> <form name=\"csrf\" action=\"http://amazon.com/gp/ product/handle-buy-box\" method=\"post\" target=\"hidden\"> <input type=\"hidden\" name=\"ASIN\" value=\"059600656X\" /> <input type=\"hidden\" name=\"offerListingID\" value=\"XYPvvbir%2FyHMyphE%2Fy0hKK%2BNt%2FB7% 2FlRTFpIRPQG28BSrQ98hAsPyhlIn75S3jksXb3bdE% 2FfgEoOZN0Wyy5qYrwEFzXBuOgqf\" /> </form> <script>document.forms.csrf.submit();</script> http://shiflett.org/blog/2007/mar/my-amazon-anniversary

Slide 97: Defence against CSRF • You need to know if the form that is being submitted is one that you served up from your own site (as opposed to an evil form created by an attacker) • Include a hidden form field with a token generated by your site and associated with the logged in user in a non-predictable way

Slide 98: Building sites that scale

Slide 99: Scalability is not performance

Slide 100: Scalability is not performance Scalable systems increase their performance as new hardware is added, proportional to the hardware’s capacity

Slide 101: Vertical v.s. horizontal • Vertical scaling: buy a bigger machine • More RAM • More CPU(s) • “Big iron” costing $100,000+ • Horizontal scaling: buy more machines • Almost always better than vertical scaling • But... software must be designed to scale out

Slide 102: “Premature optimisation is the root of all evil” - Tony Hoare and Donald Knuth

Slide 103: http://blog.ilike.com/ilike_team_blog/2007/06/holy_cow_6mm_us.html

Slide 104: “Shared nothing” • Rasmus Lerdorf, the creator of PHP, describes this as a key principle of scaling • Application servers (web servers running PHP) have no shared state - everything stateful is pushed out to the database layer • This lets you trivially horizontally scale your application servers behind a load balancer • Now you just have to scale the data layer...

Slide 105: Four steps to building a scalable data layer • Add caching • De-normalise where necessary • Add database replication • Add sharding

Slide 106: Caching • You could cache to disk or shared memory... • ... but you’re better off using memcached • Distributed key/value in-memory caching system, first developed for LiveJournal • Facebook,YouTube, Wikipedia, Flickr... obj = memcache.get(obj_id) if not obj: obj = construct_obj_from_database(obj_id) memcache.put(obj_id, obj) return obj

Slide 107: “Normalised data is for sissies” Cal Henderson, Flickr • You can get a major speed-up by duplicating some data (e.g. counts) in your database • Your application logic will need to keep everything in sync

Slide 108: Replication • Master-slave replication lets you set up copies of the database to accelerate reads Writes all go to master Master Slave Slave Slave Reads spread across all slaves

Slide 109: Replication • Master-master replication provides redundant masters, but doesn’t really improve write performance (both still have to make the same number of writes) Writes all go to masters Master Master Slave Slave Slave Reads spread across all slaves

Slide 110: Sharding • Sometimes known as federation • Users 1-1000 are on database A, 1000-2000 are on database B... • Often requires a large scale re-write of the system • Much harder to do in social applications where relationships span multiple databases • WordPress MU is an interesting case-study

Slide 112: Scalable business models • Scaling gets a lot easier if you build it in to your business model • 37signals products (Basecamp, Highrise) shard naturally based on individual customer accounts - and more customers means more money for servers • Second Life shards by land area, and land has to be bought by users - they’re essentially a 3D web hosting company

Slide 113: Build it on Amazon • S3 - Simple Storage Service • Cheap, robust key-value storage of both small and large files • EC2 - Elastic Compute Cloud • On-demand instant virtual servers, billed by the hour • SQS - Simple Queue Service

Slide 114: Thank you!

Slide 115: Thank you!