presented at the Denver Open Source Users Group 8/2/2011

1. node.js
asynchronous...
for the rest of us
Mike Brevoort
8.2.2011
DOSUG
code sample can be found at
https://github.com/mbrevoort/node.js-presentation

2. agenda
the case for node.js
developing with node
look at a few popular modules
lessons from the trenches

4. typical n-tier
run-a-round
browser makes call to web server
(waits)
web server makes call to database
(waits)
web server returns result to browser
Response time is dominated by time waiting

5. typical i/o latency
L1: 3 cycles
L2: 14 cycles
RAM: 250 cycles
DISK: 41,000,000 cycles
NETWORK: 240,000,000 cycles
L1
L2
RAM
Disk
Network
0 60,000,000 120,000,000 180,000,000 240,000,000 300,000,000
http://nodejs.org/jsconf.pdf

6. http://xach.livejournal.com/
170311.html

7. “Most languages were designed to
solve computational problems, but
Node.js is different.
Node.js was designed from the
ground up to efficiently handle the
communication that is at the heart
of modern web applications.”
http://www.joyentcloud.com/products/smart-appliances/
node-js-smartmachine/

8. node.js
An Evented I/O network server
for Javascript
created by sponsored by
Ryan Dahl

9. Runs Javascript, but isn’t
primarily Javascript
http://platformjs.wordpress.com/2010/11/24/node-js-under-
the-hood/

10. Why Javascript?
most widely used programing
language of the web
“never under estimate the power of familiarity and
friendliness” - Stacey Higginbotham, GigaOM
async by nature - the browser
is a single threaded event
loop
BAH! It’s a toy language!

11. the event loop
single threaded = no execution
concurrency
all execution initiated by an event
events may have zero to many
callbacks
events are executed in order
Tom Hughes-Croucher’s postman
analogy

12. Installing node
mac, linux or windows (with cygwin hell)
fear not! stable windows support coming
in v0.6.0 (~3wks)
# clone the git repo
git clone git://github.com/joyent/node.git
cd node
# checkout the version you want
git checkout v0.4.10
# build and install
./configure
make && sudo make install

13. Running Node
~/ node
> var x=1, y=2, z=3;
> x+y+z
REPL
6
> require('fs').statSync('./blocking.js')
{ dev: 234881026,
Read-Eval-Print-Loop ino: 3162208,
mode: 33188,
nlink: 1,
.....
node app.js arg1 arg2
Invoke script process.argv[0]
process.argv[1]
===
===
"node"
"app.js"
process.argv[2] === "arg1"
process.argv[3] === "arg2"

14. Hello World HTTP
Server
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello Worldn');
}).listen(8080, "127.0.0.1");
console.log('Server running at http://127.0.0.1:8080/');

15. Not just HTTP
var net = require('net');
var server = net.createServer(function (socket) {
socket.write("Echo serverrn");
socket.pipe(socket);
});
server.listen(1337, "127.0.0.1");
http://nodejs.org/

16. simple irc demo

17. Developing with
Node
install node
install npm
your favorite text editor
Sublime Text 2, Textmate, vim,
Emacs, Eclipse, whatever

18. npm
node package manager
created by
Isaac Schlueter (Joyent)

19. npm
publish, install, discover,
and develop node programs
puts modules in a place where
node can find them
manages dependencies

20. npm search, install
# install a module (copy to node_modules)
npm install socket.io
# install a specific version
npm install socket.io@0.6.0
# install module globally
npm install socket.io -g
# search
npm search socket
#info
npm info socket.io

21. npm registry
http://registry.npmjs.org/

22. npmjs.org stats

23. {
"name": "express",
package.json
"description": "Sinatra inspired web development framework",
"version": "3.0.0",
"author": "TJ Holowaychuk <tj@vision-media.ca>",
"contributors": [
{ "name": "TJ Holowaychuk", "email": "tj@vision-media.ca" },
{ "name": "Aaron Heckmann", "email": "aaron.heckmann+github@gmail.com" },
{ "name": "Ciaran Jessup", "email": "ciaranj@gmail.com" },
{ "name": "Guillermo Rauch", "email": "rauchg@gmail.com" }
],
"dependencies": {
"connect": ">= 1.5.2 < 2.0.0",
"mime": ">= 0.0.1",
"qs": ">= 0.3.0"
},
"devDependencies": {
"connect-form": "0.2.1",
"ejs": "0.4.2",
"expresso": "0.8.1",
"hamljs": "0.5.1",
"jade": "0.13.0",
"stylus": "0.13.0",
"should": "0.2.1",
"express-messages": "0.0.2",
"node-markdown": ">= 0.0.1",
"connect-redis": ">= 0.0.1"
},
"keywords": ["framework", "sinatra", "web", "rest", "restful"],
"repository": "git://github.com/visionmedia/express",
"main": "index",
"bin": { "express": "./bin/express" },
"scripts": {
"test": "make test",
"prepublish" : "npm prune"
},
"engines": { "node": ">= 0.4.9 < 0.7.0" }
}

24. npm install .
package.json isn’t just for
modules published to npm
npm can help you manage and
install dependencies in any
project
# from the same directory
# as package.json
npm install .

25. npm list
~/ npm list
my_project@0.1.0 /Users/mikebre/my_project
!"# cluster@0.6.9 invalid
$ %"" log@1.2.0
!"# connect-gzip@0.1.0
$ !"# connect@1.4.6
$ $ %"" qs@0.1.0
$ %"" mime@1.2.2
!"# date@1.0.1
$ %"" require-kiss@1.0.5
!"" docco@0.3.0 extraneous
!"# express@2.3.2
$ !"" connect@1.4.6
$ !"" mime@1.2.2
$ %"" qs@0.1.0
!"" hbs@0.0.7
!"" log@1.1.0 extraneous
!"" metrics@0.1.1
!"" request-forked@1.9.8
!"" semver@1.0.6 invalid
%"# xml2js@0.1.6
%"" sax@0.1.4

26. a very strong
community
nodejs.org
Google Group mailing list
IRC #node.js on freenode
Stack Overflow, LinkedIn groups
nodeconf, node summercamp, etc.

27. debugging
ndb - command
line debugger
Eclipse debugger
plugin for V8
node-inspector
is very nice!

28. node-inspector
uses WebKit Web Inspector
# install with npm
npm -g install node-inspector
# start node-inspector
node-inspector &
# start node in debug mode
node --debug app.js

29. profiling
node-inspector optionally
supports the V8 profiler
collects CPU and heap
snapshots
Speaking of heaps...

30. garbage collection
--trace-gc option to watch GC
behavior
V8 is a VM --> must GC
tuned for the browser
20Mb - 40Mb per tab
Large node heap sizes == :(

31. GC Demo

32. several popular node
modules
http://splashinthepacific.files.wordpress.com/2010/10/looking-glass-721.jpg

33. Express
Sinatra (Ruby) inspired web
framework
created by
TJ Holowaychuk

34. Express
request routing
content negotiation
view templating and partials
session support
static file serving
fast, clean and powerful

35. Express Demo

36. a RESTful service?
cute, terse. boring
let’s do something a
bit more interesting...

37. streaming demo

38. Socket.io
Unified API for Websockets +
fallbacks
created by
Guillermo Rauch

39. Socket.io
unified API for Comet style apps
transport negotiation
server and client libraries
feature rich, above and beyond what
the websocket protocol prescribes
heartbeats, timeouts, namespacing,
volatile messages, message
acknowledgements, etc.

40. socket.io demo

41. Lessons
from the trenches

42. asynchronous
learning curve
app.get('/bar', function(req, res) {
foo.fetchSomething(function(error, something) {
if(!error) {
foo.fetchSomeOne(something, function(error, someone) {
easy to if(!error) {
foo.fetchBar(function(error, bar) {
if(!error) {
write }
res.send("we got bar: " + bar);
code else {
res.send(error.statusCode);
}
like }
});
this
else {
res.send(error.statusCode);
}
});
}
else {
res.send(error.statusCode);
}
});
});

43. uncaught errors
on error, node emits an ‘error’ event on
the corresponding object
if no listeners on object for ‘error’, a
top level exception is raised and the
process exits
>
var server = http.createServer(function (req, res) {});
prudent server.on('error', function(error) {
approach console.log("Caught error! Don't exit!");
});
nuclear
approach > process.on('uncaughtException', function(error) {
});
console.log("Kaboom.... handle " + error);

44. plan for multiple
processes from the start
each node process is bound to one core
many small processes better than one
big one
use Cluster
https://github.com/learnboost/cluster
var cluster = require('cluster');
cluster('app.js')
.set('workers', 16) // defaults to # of cores
.use(cluster.logger('logs'))
.use(cluster.stats())
.use(cluster.cli())
.use(cluster.repl(8888))
.listen('80')

45. keep the heap small
200Mb or less if you’re worried
about GC pause
move data out of the node process
instead use Redis, MongoDb, etc
encourages statelessness,
encourages scalability
reduces risk of losing a single
node process

46. everything you do
blocks
No CPU for YOU!
http://redriverpak.files.wordpress.com/
2010/08/vwtouareg-road-block.jpg

47. be weary of loops
for (var i=0, l=entries.length; i<l; i++) {
doSomething(entries[i]);
}
innocent enough?
if # entries = 10,000
doSomething() takes ~1ms
you block for 10 seconds!

48. non-blocking loops
// order matters
function processEntry(entries, index) {
index = index || 0;
if(index === entries.length) return done();
doSomething(entries[index]);
process.nextTick(function() {
processEntry(entries, index++)
});
}
processEntry(entries);

49. non-blocking loops
// order doesn't matter
var leftToProcess = entries.length;
for (var i=0, l=entries.length; i<l; i++) {
(function(foo) {
process.nextTick(function() {
doSomething(foo);
if(--leftToProcess === 0) {
done();
}
});
})(entries[i]);
}

50. non-blocking loops
// order doesn't matter
// doSomething takes callback and is Async
// doSomethingAsync's happen in parallel
var leftToProcess = entries.length;
// doSomething's will be executed in parallel
for (var i=0, l=entries.length; i<l; i++) {
(function(foo) {
process.nextTick(function() {
doSomethingAsync(foo, function() {
if(--leftToProcess === 0) {
done();
}
});
});
})(entries[i]);
}

51. set ulimit -n
node can handles 1000’s of connections?
but your OS says...
Too many open files
default # file descriptors on most linux
systems is 1024
1 FD per socket means max open sockets < 1024
increase the max # of file descriptors
ulimit -n <max # FD>
ulimit -a to see current max

52. pooled outbound
connections
node pools outbound http(s) connections by default
for host + port combinations
default concurrent maxSockets per host + port is 5
is this what you want?
// for http as of node v0.4.10
require ('http')
.getAgent("api.twitter.com", 80)
.maxSockets = 100;
// for https as of node v0.4.10
require ('https')
.getAgent({ host:"docs.google.com", port: 443 })
.maxSockets = 100;

53. timeouts
expect that any callback could fail and
may not be called
anticipate conditions where both
inbound or outbound connections may
hang
use Mikeal Roger’s ‘request’ module
I contributed timeout functionality
should be part of node core ~v0.7/0.8

54. offload anything
computationally intensive
spawn a child process
require('child_process').spawn
call out to another system
more apt to handle heavy
lifting
use a job queue

55. be specific with
package dependencies
{
"name": "Foo Package",
"description": "my Foo package",
>
"version": "1.0.0",
"author": "Mike Brevoort <mikebre@ecollege.com>",
"dependencies": {
"express": "2.3.2",
"cluster": ">= 0.6.1", is this what
"mongodb": "0.9.x",
"connect-gzip": "~0.1",
you really
"underscore": "= latest" want? really?
},
"engines": { "node": "= 0.4.8" }
}

56. Let me tell you about my
friend node
he’s a great multi-tasker but
can only do one thing at a
time

57. Thank You!
Questions?
Mike Brevoort
@mbrevoort
mike [at] brevoort [dot] com