3rd Generation Web Application PlatformsNaresh Chintalcheru

1st Generation

CGI : Common Gateway Interface

CGI Scripting languages▪CGI C▪CGI Perl▪CGI TCL▪CGI Basic

One Process per User Request

[Operating System Processes, Threads, Semaphores, Mutexes and Barriers, are the scheduling mechanisms to acquire the time slices of the CPU. The Processes are expensive and consume more resources than Threads]

Drawbacks:

▪ The CGI script interpretation (compile + execution) happens at the request processing time.

▪ One user request spawns one Process, locking all the allocated resources even though request processing might not need it.

▪ The CGI spawned Process is outside the Web Server control.

2nd Generation

ISAPI Engines

ISAPI : Internet Server Application Programming Interface

2nd Generation Platforms

▪ J2EE▪ .Net▪ LAMP▪ Ruby on Rails▪ Groovy on Grails

What is common in the 2nd generation platforms ?

Multi-Threaded Runtime

One Thread per User Request

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JEE Request-To-Thread

Spring DispatcherServlet

JSF FacesServlet

Struts ActionServlet

Request 1

Request 2

Request .. n

One Servlet instance on the App Server spawns a new thread for each user request

Thread 1

Thread 2

Thread .. n

Application Server

Drawbacks:

▪ One thread per user request locks the resources allocated to the thread at the time (wait) of I/O operations.

▪ Context-switching between threads are expensive.

3rd Generation

Single Thread Runtime

One Thread for [many] Users Request

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How it is possible one Thread can serve multiple users ?

▪Lets see how many cycles it takes for a Disk I/O

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▪It takes around 41 million cycles to do a disk I/O.

▪For a network call 240 million cycles ….

“Understanding Node Event-Loop” – Must read excellent blog post from Mixu.

▪Swim into the micro millisecond world.

▪Everything in the multi-threaded server is …..

Waiting … Waiting … Waiting … Waiting …Waiting … Waiting … Waiting … Waiting …Waiting … Waiting … Waiting … Waiting …Waiting … Waiting … Waiting … Waiting … Waiting … Waiting … Waiting … Waiting . Waiting … Waiting … Waiting … WaitWaiting…Waiting…Waiting…WaitWaiting … Waiting …Wait

▪While the user request is waiting for an I/O operation, the 3rd generation platforms use Non-Blocking I/O based call-backs managed by an Event-Loop and the Thread will move on to the next request.

▪The whole thing happens so fast that one Thread will be able to respond to multiple user requests.

3rd generation platforms

▪Node.js for JavaScript▪Vert.x for Java▪Libevent for C▪Twisted for Python▪EventMachine for Ruby

3rd generation platforms

The rest of the presentation will focus on

Node.js

Unbelievable Concurrency ?

▪ Assuming each thread has 2 MB of memory running on 8 GB of RAM puts it at a theoretical maximum of 4000 concurrent connections, plus the cost of context-switching between threads.

▪ That’s the scenario you typically deal with in traditional web-serving techniques. By avoiding all that, Node.js achieves scalability levels of over

1Million concurrent connections (as a proof-of-concept).

The 3rd generation platforms use the combination below to efficiently utilize the OS resources.

Single Thread Non-Blocking I/O

Event Loop

Node.js▪ Platform based Server-side JavaScript▪ Event-Driven Concurrency Model▪ Use single thread and non-blocking I/O▪ JSON and JavaScript are practically siblings that translate to Nodes▪ JavaScript is a dynamically typed language▪ Real-time web applications employing server-side push and two-way connections where server and client can initiate communication

▪ I/O Operations executed in parallel but not the code

▪So throw-out JEE/.Net applications and rewrite in node.js ?

Node.js makes it an excellent choice

for I/O based Applications.

What are I/O based Applications?Applications which connect to databases, make web service calls, use files for logging and make connections to MQ, Mail & LDAP servers.

Node.js is not a good choice for CPU intensive Applications.

(Node pundits argue that CPU intensive components should be evented and passed onto another thread)

What are CPU intensive Applications?Applications which does lot of data processing on the App server and complex calculations which need more CPU time.

Node.js itself is not Non-Blockingfunction getAge(user_id) { sql = 'SELECT age FROM users WHERE id = ' + user_id; connection.query(sql, function(err, rows, fields) { if (err) throw err; return rows[0].age; });return 0;}

[The above database call code will starve the thread and node will not respond to other users]

Below Node.js code will unblock I/O and respond to other users

function getAge(user_id, callback) { sql = 'SELECT age FROM users WHERE id = ' + user_id; connection.query(sql, function(err, rows, fields) { if (err) throw err; var age = rows[0].age; callback(age); });}

[The above database call code uses callbacks and unblock the I/O]

Programming for Node.js requires clear understanding of:

▪Asynchronous code▪Event-Driven▪Non-Blocking I/O▪Callbacks and Promises

Who is using Node.js ?

Paypal, LinkedIn, eBay,

Yahoo, Walmart ……………

http://nodejs.org/industry/

Node.js does not frameworks ?

Ever growing list of presentation, data persistence and many more frameworks ……………

http://nodeframework.com/

With the ever growing cost of hardware, power to cool them and long maintenance cycles ….

How long will enterprises withstand the temptation of

3rd Generation Platform ?

Disclaimer:The views and opinions expressed in this article are those of the author. The metrics and numbers used in this presentation are from the open blogs which are not validated. This is a technical presentation which will make you think about the new platform options in the technology.

References:▪ http://labs.vmware.com/vmtj/autonomous-resource-sharing-for-multi-

threaded-workloads-in-virtualized-servers▪ http://adamgent.com/post/10440924094/does-java-have-an-answer-to-

node-js▪ http://www.toptal.com/nodejs/why-the-hell-would-i-use-node-js▪ http://blog.caustik.com/2012/08/19/node-js-w1m-concurrent-connections/▪ http://bijoor.me/2013/06/09/java-ee-threads-vs-node-js-which-is-better-for-

concurrent-data-processing-operations/▪ http://www.ibm.com/developerworks/java/library/j-nodejs/index.html▪ http://www.qnx.com/developers/docs/6.4.1

/neutrino/getting_started/s1_procs.html#More_synchronization▪ http://zef.me/5390/decoupling-events-vs-dependency-injection▪ http://highscalability.com/blog/2013/3/18/beyond-threads-and-callbacks-

application-architecture-pros-a.html▪ http://stackoverflow.com/questions/4296505/understanding-promises-in-

node-js