NodeJS - Server Side JS


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Node JS - Server side JS platform. An introduction.

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NodeJS - Server Side JS

  1. 1. Node.js – Server Side JavaScript GaneshKondal June 13, 2014
  2. 2. Agenda • Intent • Node JS – Background & Overview • JS Basics • Pre-Cursors • Installation, Setup, IDE & NPM • JS Basics – callback, blocking & non-blocking I/O • NodeJS –Modules, simple server • Node JS Architecture • Blocking vs. Non-Blocking I/O – Comparison • Web Application with Express MVC • Project – Code Structure • App Development Sequence • Code Parts – UI Template, Router, Database invocation • Industry Adoption • Applicability – Suited / Not Suited for • Next Session – Topics
  3. 3. Intent • To introduce listeners to the NodeJS platform; discuss the key aspect of non- blocking I/O; run through a sample web app developed using Express framework • An hour of glimpsing around NodeJS – Nothing else Follow-up Follow-up sessions will extend the sample application to work with files, show case a socket I/O based file explorer and integrate with NoSQL databases like MongoDB
  4. 4. 4 Node JS – Background • Node.js runs on V8 Javascript Engine • V8 is Google’s open source engine; written in C++ for Chrome • Created by Ryan Dahl in 2009 and first published in 2011 • Runs on Linux and Windows • Development and Maintenance of NodeJS is done by Joyent • Written in C/C++ (80%) and JavaScript (20%) and it is open source. Overview • Node.js is ‘server-side JavaScript’; event-driven async I/O • Well optimized for high concurrency, high performance and network applications • Uses an event-driven, non-blocking I/O model. • Non-blocking I/O happens via JavaScript’s callbacks. • Programs for Node.js are written in JavaScript [not DOM manipulation like in jQuery] • Node JS executes in a single threaded fashion
  5. 5. 5 Pre-Cursors • Installation • From website or • Homebrew (mac OS) or Synaptic (Ubuntu) • IDE – • JetBrains WebStorm 8.0.1 OR • Sublime Text OR • Eclipse with nodeclipse • NPM • Node Package Manager enables get third party modules • Two modes • Global - installs modules c:users356992appdata… • Local – in the same directory under node_modules • Works based on package.json in the root folder • Comes packaged with Node installation Open Source Node Repository
  6. 6. 6 JavaScript – Basics s1 s2 s3 s4 s5 • Functions in JavaScript are objects – first class citizens • Essentially, you can pass a function as a variable to another function call • Closure Callbacks are – a Functional programming paradigm Callbacks a.k.a Higher- Order function Only the function definition is passed; function is not executed A closure is an inner function that has access to the outer (enclosing) function’s variables—scope chain • When callback is invoked, if there is a ‘this’ reference; it will be ‘undefined’ • Handling ‘this’ in a callback is via JS methods of ‘apply(..)’ or ‘call(..)’ OR • Have the ‘this’ stored in a variable called ‘self’ and use it.
  7. 7. 7 Event Driven Programming – Blocking, Non-Blocking I/O s1 s2 s3 s4 s5 Traditional I/O Non-blocking I/O var result = db.query(“select x,y from tableXY”); doSomethingWithResult(result); //waits for the result! doSomethingWithoutResult(); //execution is un-necessarily blocked! db.query(“select x, y from tableXY”, function (result){ // gets called once the result is ready! doSomethingWithResult(result); }); doSomethingWithoutResult(); //executes without any delay! Callback on db query completion event
  8. 8. 8 Fundamentals – Modules, Sample Code • Modules • Referenced by file path or file name • No Global Scope in NodeJS • Modules are loaded only once • Libraries in node are packages/modules Module 1 Module s5 s1 s2 s3 s4 s1 s2 Global Scope Scripts within a module context • Sample – Web Server in 3 lines Classic Browser Runtime Node Runtime & Scope s3 s4 s5 Loads the ‘http’ module Function that handles the incoming requests. Executed by the main thread of node.
  9. 9. Multi-Threaded HTTP Server – Blocking I/O • On heavy load – we see more threads that leads to more context switching which in turn leads to more CPU / Memory usage • Classic discussion on threads vs. events is in Benjamin Erb’s Thesis [Strongloop, 2014]
  10. 10. Node JS Architecture – Non-Blocking I/O • On heavy load – we see more threads that leads to more context switching which in turn leads to more CPU / Memory usage • Classic discussion on threads vs. events is in Benjamin Erb’s Thesis [Strongloop, 2014]
  11. 11. Node JS – Event Loop • Node is single-threaded • Follows an event-driven functional programming model • Errors in the main thread kills the server • POSIX thread switching is not costly Million concurrent connections [, 2014]
  12. 12. Node JS – Event Loop Client Event loop (main thread) C++ Thread pool (worker threads) Clients send HTTP requests to Node.js server An Event-loop is woken up by OS, passes request and response objects to the thread-pool Long-running jobs run on worker threads Response is sent back to main thread via callback Event loop returns result to client • Node is single-threaded • Follows an event-driven functional programming model • Errors in the main thread kills the server Million concurrent connections
  13. 13. Java vs. NodeJS –Performance [ Return data with constant sleep] Java Stack & Description • Java servlet returns ‘hello world’ with a 200ms sleep [ simulating a 200ms DB call] • Executed in Apache Tomcat 6.0, JDK 6 • Tomcat runs in a multi-threaded mode & in a blocking mode Node v 0.10 • Returns a ‘hello world’ equivalent string with a 200ms timeout set in call • Node JS ran in the (defacto) non-blocking mode Not a comparison between Java vs. Node – rather a comparison of blocking and non- blocking I/O
  14. 14. Node JS – Run Sample Web Application • Use cases we will see • Get the list of players from NoSQL (MongoDB) • Add a player to the list • STEP 1 – setup • Install Node • Install Express • Install Expres – Genertor • Generate a node express project • Install MongoDB • STEP 2 – Package.json edit to suit your needs • STEP 3 – Install dependencies • STEP 4 – Run d:nodejs> npm install express d:nodejs> npm install express-generator d:nodejs> express playerlist d:nodejsplayerlist> npm install d:nodejsplayerlist> npm start
  15. 15. Node JS – Project Structure Jade HTML Preprocessor Express Engine Mongo DB Monk Node.js Server d:nodejs> npm install express d:nodejs> npm install express-generator d:nodejs> express playerlist V M C Public images, CSS and JS files URI routing; view attachment View templates using Jade. Multiple other options exists – ejs, jade Mongo DB Data files • Jade – Template engine. Very short syntax to create a HTML • Monk – Small layer that enables MongoDB a super-easy task within NodeJS
  16. 16. Node JS – Code Parts – MVC 1) Import necessary modules 2) Initialize Express 3) Configure the express app a. Logger b. Views c. Template engine d. Static images directory e. … 4) Configure the router 5) Router = Controller a. Connects the model, jade view b. Enables navigation across the URIs
  17. 17. Node JS – UI Template • Jade is a server side templating engine – like Thymeleaf, JSP, ASP • Short syntax to create HTML
  18. 18. Node JS – Code Parts contd. • Router • Database View: Jade template name View Model: “Model of the view” JSON object passed to the view 1 2 3 Load ‘Mongo’, ‘Monk’ necessary to connect to MongoDB Put the Mongo DB reference handle to the global request object db.get - Monk APIs to fetch db.insert,db.find({},fn) are some of the other relevant APIs
  19. 19. Node JS – Deployment • Simplistic – Newbie mode • node server.js • Command line execution. No restart; or no monitoring • Dies with the command shell closing • Little better • node server.js & • Running as a background application in *nix • Will last than the shell that started it • Script that loops & restarts the server • Still limited the lifeline of the script that starts • Improvised shell • Cron based monitoring • Log attached • Auto start enabled • External port monitoring enabled for load balancing While : do // node server.js // sleep x seconds done // description // author // specify port, Ethernet card // attach a cron job – for every minute // start in sudo mode // ensure a log file is rolled // attached the init.d in linux
  20. 20. 20 Industry Adoption Paypal’s Account Overview via NodeJS • Timeline & Inventory • Built twice as fast as the Java Application • 33% fewer lines of code – compared to the same functionality in Java /Spring • 40% fewer files • Performance • Double the requests vs. Java Application • 35% decrease in the average response time • Essentially, page loading is faster than the Java App • Stack • NodeJS – Server • KrakenJS – Secure and scalable layer that extends Express, which provides convention • Dust – Asynchronous templates
  21. 21. 21 Pros & Cons Pros • Fast – Execution speed • Faster to market – development speed • Less lines of code • Great community • Proven with high volume systems • Most suited for networking, I/O intensive applications Cons • Writing event driven code is complex compared to synchronous code • Writing a large business logic centric system is cumbersome • Callback hell • Exception handling is not straight forward
  22. 22. 22 Suitability Suitable Scenarios • Most suited for networking, I/O intensive applications • Applications that need high concurrency / Queued concurrent inputs • Streaming Applications – like Chat servers • Proxy Service • Real time applications • Monitoring Dashboards • like Brokerage Dashboard (Node JS + Socket IO) • Application Monitoring • REST APIs Not Suited For • Large business logic centric systems • Heavy server side computation is required
  23. 23. Next Session • File handlers, Streams • Event Emitters • Error, Exception Handling • Socket.IO • Build & Deploy – using Grunt • JS CoE – Seed project for node
  24. 24. Thank You 24
  25. 25. Reference • Ryan Dhals original presentation in JS Conf • Expess framework • • Node JS - • Event Loop – • Strongloop – how nodejs is faster
  26. 26. Reference 26 THANK YOU
  27. 27. Appendix 27 Appendix
  28. 28. Why Node JS is faster [ Return data with constant sleep] • Asynchronous Non-blocking I/O is the root cause • Not just I/O alone – all of node js 50k modules are written in an async fashion • Debuggers, monitors, loggers, • Cluster manager • File operation • Java NIO alone is not enough