Web Applications For The Cloud - Virginia Tech

Web Applications For The Cloud - Virginia Tech

Building Web Applications For The Cloud Godmar Back 9/14/2012 Dept of CS Colloquium 1 Do You Doodle? 9/14/2012 Dept of CS Colloquium 2 Todays Web Technology Landscape

9/14/2012 Dept of CS Colloquium 3 Ok, Lets Build That Model View Controller - MVC Mock up a View (in Jade) and test it. Write your Model (in CoffeeScript) Two supporting classes

A model singleton. and unit test it. Trygve M. H. Reenskaug (in 1979) Yes, professional developers do that. Use AngularJS to create a descriptive Controller and wire the model to the view. 9/14/2012 Dept of CS Colloquium 4 Presenting: The Meeting Scheduler The brand-new Meeting Scheduler Application

9/14/2012 Dept of CS Colloquium 5 Are We Done Yet? Wait Are we really running in the cloud? No! Were running downloaded code in a JavaScript sandbox on the machine in front of us.

9/14/2012 Dept of CS Colloquium 6 Reality Sets In Client 9/14/2012 Server Dept of CS Colloquium 7 The Web Is A Distributed System

Ok. Rethink. Data must be kept on the server. Somehow. Another technology pile: AJAX, CometD, JSON-P, REST, RPC Model Another model? Model View View-Model? Which parts should be kept on client? All? Some? When to synchronize the client and server models? Do I need a submit button? What if the user refreshes or revisits the page? Looking for inspiration 9/14/2012 Dept of CS Colloquium 8

Introducing CloudBrowser Client Server cloudbrowser.cs.vt.edu 9/14/2012 Dept of CS Colloquium 9 CloudBrowser Architecture Server-side JS Environment (node.js) Web Browser Virtual Browser Forwards Events

Client Engine Web Socket Connection Listens for Events Applies Updates Sends Updates JS Web Application CSS, Images Server Engine Dispatches

Events Parses HTML Observes Changes Data Bindings DOM DOM Delivers Events JavaScript Application

Code JS Libraries (jQuery, AngularJS) node.js Libraries Other Tiers Modifies DOM JSDOM, Contextify 9/14/2012

Dept of CS Colloquium 10 Implementation Implementation Platform Processing Client Events Synchronization Protocol Detecting Virtual Browser Changes JavaScript Execution 11

Implementation Platform Node.js Built on Google s V8 JavaScript Engine One language client- and server-side Automatic integration with virtual browser Large library ecosystem, e.g. email Controller JSDOM Node.js W3C DOM implementation Socket.io 2-way socket connection between browser and server 12 Processing Client Events Block normal client-side event processing Register capturing event listeners on those events Call event.stopPropagation() Call event.preventDefault()

13 Synchronization Protocol We establish RPC endpoints on the client and server. Client Methods PageLoaded(records) DOMNodeInsertedIntoDocument(records) DOMNodeRemovedFromDocument(records) DOMAttrModified(target, name, value) DOMPropertyModified(target, property, value) DOMCharacterDataModified(target, value) DOMStyleChanged(target, attribute, value) AddEventListener(target, type) PauseRendering() ResumeRendering() Server Methods

processEvent(event) setAttribute(target, attribute,value) 14 Detecting Server-side DOM Updates Changes detected using aspect-oriented method Add wrapper methods (advice) around DOM manipulation methods. Example: var oldMethod = DOM.Node.appendChild; DOM.Node.appendChild = function () { var rv = oldMethod.apply(this, arguments); browser.emit('DOMNodeInsertedIntoDocument', { target: arguments[0], parent: this

}); return rv; }; 15 JavaScript Execution Each virtual browser needs a faithful JavaScript environment Must match existing browser environments Required to run existing client-side libraries Node.js didnt expose an API to provide isolated execution environments with the right semantics window === this? We wrote Contextify, a C++ addon for Node Adopted upstream by JSDOM 16

Evaluation Goals What is the latency cost of processing events on the server? Whats the memory cost of instantiating virtual browsers on the server? Whats the memory cost of adding additional clients to a virtual browser (co-browsing)? How good is our DOM implementation? 17 Evaluation Setup Hardware: Server: 2- 2.5 GHz quad-core processors, 16 GB RAM Client: 3.00 GHz quad-core processor, 8 GB RAM Connected by gigabit LAN Cant use traditional benchmarking means

CloudBrowser isnt stateless We want to simulate user interactions with a virtual browser 18 Latency Response times (Nielson, Usability Engineering) < 100ms: feels instantaneous < 1 second: noticeable, but doesnt interrupt workflow Keynote Internet Health report considers latency < 90ms between backbones as good Ping from Blacksburg to Austin, TX: ~60 ms 19 Latency

20 Latency (Human User) 21 Virtual Browser Memory Usage Question: whats the memory cost of a virtual browser? Experimental procedure: Connect a client to a new virtual browser (cause allocation) Force a garbage collection Collect V8 heap memory usage (Node.js API) 22 Virtual Browser Memory Usage

Application Hello World Chat Room Meeting Scheduler Memory Usage 164 KB 2.58 MB 4.45 MB Effect of JavaScript: jQuery: 1.05 MB Knockout.js: 0.33 MB Moment.js: 103 KB Effect of CSS: Bootstrap: 820 KB 23

Additional Client Memory Usage Question: whats the memory cost of adding clients to a single virtual browser? Experimental procedure: Connect a scripted client to the virtual browser Force a garbage collection Collect memory usage Result: ~16 KB per connected client 24 DOM Conformance jQuery Test Suite Results Test Suite Core

Callbacks Deferred Support Data Queue Attributes Events Selector Traversing Manipulation CSS AJAX Effects Dimensions Exports Offset Selector (jQuery) Pass

1306 418 155 28 290 32 453 476 310 297 530 58 329 367 61 1 N/A N/A

Total 1309 418 155 38 290 32 473 482 314 298 547 93 349 452 83 1 N/A N/A

% Passed 99.77% 100.00% 100.00% 73.68% 100.00% 100.00% 95.77% 98.76% 98.73% 99.66% 96.89% 62.37% 94.27% 81.19% 73.49% 100.00%

25 Limitations (1) No access to computed layout Cant support libraries that rely on client-side layout information. element.offsetWidth, element.offsetTop, etc. CSS3 can eliminate this need for many use cases Can encapsulate client-side components Highly latency-sensitive applications (e.g. games) Not every application should be a CloudBrowser application. 26 Limitations (2) DOM conformance

Lacking support for browsing pages in the wild (though remarkably good) As JSDOM implementation improves, so does CloudBrowser Multi-core scaling Node.js is event-based & single-threaded Need to distribute framework to multiple processes Initial implementation done, but requires improvement 27 Scaling to Multiple Processes pipe Virtual Browser pipe

Virtual Browser pipe Virtual Browser Client Browser Front-end Server app1 Server (multiprocess) app2 Server (single-process)

Virtual Browser Virtual Browser 28 Related Work: Contemporary AJAX Web Applications E.g., insert (client-library) + (server-framework) here Changing programs requires both client and server programming. Model-View-Controller pattern is distributed. Distributed controller logic. Client-side state is transient Lost on page refresh and navigation Reconstructing client-side state is difficult

No unique mapping of URLs to particular views Network programming manually handled by developer. 29 Related Work: Existing Server-centric Frameworks ZK, ItsNat, Echo2, Vadiin, IceFaces Client-side state is still transient Components instantiated on each request Client state must be manually reconstructed Difficult to debug due to component translation process Designers and developers must learn new markup and programming languages 30 Future Work

CloudBrowser as a PaaS offering Multi-process scaling improvements Improved CloudBrowser API Improved DOM conformance Virtual browser management: Persistence Garbage collection 31 Conclusion CloudBrowser is a server centric web application framework where applications run in virtual browsers

on the server Actual rendering takes place on the client User interface state is automatically preserved across navigation, refresh, and disconnect CloudBrowser introduces acceptable latency and memory overhead for many use cases The distributed nature of web applications is hidden from developers 32 Acknowledgements Brian McDaniel, Virginia Tech, MS 2012 Main implementer of CloudBrowser Open GRA Position Now Supported by CAREER: CCF-SHF Advanced Execution Environments for Next-generation Cloud Applications Brian McDaniel & Godmar Back, The CloudBrowser Web

Application Framework, to appear at Systems, Programming, Languages and Applications: Software for Humanity (SPLASH12) Wavefront, Oct 2012, Tucson AZ 9/14/2012 Dept of CS Colloquium 33

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