google application engine introduction jim eng with thanks to charles severance :
TRANSCRIPT
Google Application Engine
Introduction
Jim Eng
with thanks to Charles Severance
http://www.appenginelearn.com/http://www.dr-chuck.com/
Cloud Computinghttp://en.wikipedia.org/wiki/Cloud_computing
LocalNetwork
Pre-Cloud View
The Internet
...
Router
HardwareHardware
SoftwareSoftware
ctools.umich.edu
In a pre-cloud view servers have a
geographic location and we use the
Internet to exchange data with those
servers.
World-Scale Applications
•For world-scale applications - the servers must be distributed around the world
•But users must see a uniform “single image” - www.google.com
•Also the programmers cannot know the structure or grography of the servers - because this always changes
Google Server Locations
http://royal.pingdom.com/2008/04/11/map-of-all-google-data-center-locations/
This is an educated guess.
Programming in the Cloud
•Programmers operate in a controlled environment
•Programs do their programming thing - code + data
•A complex software framework manages getting the right code and data to/from the right servers.
•Software developers are unaware of geography
The geographic location no longer
matters - the software “runs
somewhere in the cloud”.
Resources can be dynamically adjusted as load changes.
LocalNetwork
Pre-Cloud View
The Internet
...
Router
SoftwareSoftware
Server Server Busy?Busy?
Post-Cloud ViewThe Cloud
...
My My CodeCode
My My CodeCode
Your Your CodeCode
My User
My User
Your User
HTTP - Request / Response
•The nature of the HTTP Request/Response cycle makes the cloud possible
•Since clients are not connected for very long - the cloud can be changed in between requests
•As long as the cloud “fakes” everything about the protocol - no one is the wiser..
•The cloud engineers at Google/Amazon/Yahoo are pretty clever.
HTTP Request / Response Cycle
http://www.oreilly.com/openbook/cgi/ch04_02.html
Browser
Web Server
HTTPRequest
HTTPResponse
Internet Explorer, FireFox, Safari,
etc.
HTTP Request / Response Cycle
http://www.oreilly.com/openbook/cgi/ch04_02.html
Browser
Web Server
HTTPRequest
HTTPResponse
Internet Explorer, FireFox, Safari,
etc.
GET /index.html
<head> .. </head><body><h1>Welcome to my application</h1> ....</body>
Post-Cloud ViewThe Cloud
My My CodeCode
My My CodeCode
Your Your CodeCode
My User
Post-Cloud ViewThe Cloud
My My CodeCode
My My CodeCode
Your Your CodeCode
My User
GETGET
Cloud Summary
•The cloud is the Internet plus computing that is “embedded” “inside” the network
•Companies like Google, Amazon, and Yahoo put servers all over the world
•Software runs on whichever server is most appropriate and data/code is moved around and the cloud can be reconfigured dynamically
Materials
•Google Application Engine
•Free hosted web services using Python
•http://code.google.com/appengine/
•We will be using web materials and making materials as we go.
Overview Video
•Builds a Google App Engine application in 10 minutes
•Basic structure - GET / POST
•Form Input
•Templating
•Database
http://www.youtube.com/watch?v=tcbpTQXNwac
Google App Engine
Google App Engine
•Expose Google’s worldwide Infrastructure to us as developers
http://www.youtube.com/watch?v=3Ztr-HhWX1chttp://www.youtube.com/watch?v=tcbpTQXNwac
Google App Engine•When you write a Google Application Engine
Application - you are running in the Google Cloud
• Just like you were a Google Developer
•You don’t know where you are running or if one copy of a thousand copies of you are running
•Google hosts small applications for *free* - larger applications pay by usage
Free Accounts• A free account
can use up to 500MB of persistent storage and enough CPU and bandwidth for about 5 million page views a month.
Installing Google App Engine
http://code.google.com/appengine/downloads.html
Your First Web Application
app.yaml - Tells Google about the applicationindex.py - the code for our application
File -> Add Existing ApplicationPick Your Directory
/Users/csev/a539/apps/ae-01-trivial
Select your new application and press “Run”. When it has a little green symbol
- then press “Browse”.
Yay!
Remember to ignore files with tildes (~)or
JEdit -> Utilities -> Global Options -> Autosave & Backupand set the number of backups to zero
A Second ApplicationDumping Input data
Dumper•This application makes a form and then we
submit the form via POST
•This application dumps the input variables that come in from the HTTP Request
•This is the most basic view of a web application
• It is like a Dinosaur - it is a web program written using the “old ways”
Common Gateway Interface
•A set of rules about taking input parameters and data from an incoming HTTP request and handing them to the program.
HTTP Request / Response Cycle
http://www.oreilly.com/openbook/cgi/ch04_02.html
Browser
Web Server
HTTPRequest
HTTPResponse
HTTP Request / Response Cycle
GET /index.htmlAccept: www/sourceAccept: text/htmlUser-Agent: Lynx/2.4 libwww/2.14
http://www.oreilly.com/openbook/cgi/ch04_02.html
Browser
Web Server
HTTPRequest
HTTPResponse
<head> .. </head><body><h1>Welcome to my application</h1> ....</body>
Passing Parameters to The ServerGET /simpleform.html?
yourname=fredAccept: www/sourceAccept: text/htmlUser-Agent: Lynx/2.4 libwww/2.14
POST /cgi-bin/program.pl HTTP/1.0Accept: www/sourceAccept: text/htmlUser-Agent: Lynx/2.4 libwww/2.14Content-type: application/x-www-form-urlencodedContent-length: 13yourname=fred
HTTPRequest
Browser
Web Server
<input type="text" name="yourname" id="yourid" />
http://hoohoo.ncsa.uiuc.edu/cgi/in.html
CGI In App Engine
•When a Request is received in the App Engine, according to the rules of CGI
•The environment variables such as server name, document path, etc come in a dictionary object
•Any POST data comes in on standard input (sys.stdin)
•Whatever the program prints goes to the browser as the HTTP response
<form method="post" action="/">Zap Data: <input type="text" name="zap"><br>Zot Data: <input type="text" name="zap"><br><input type="submit"></form>
EnvironmentData
POST Datazap=Stuff&zot=MoreStuff
dict()
stdin
<form method= ....></form>
CGIProgram
BBrroowwsseerr
import osimport sys
print 'Content-Type: text/html'print ' 'print '<form method="post" action="/">'print 'Zap Data: <input type="text" name="zap"><br>'print 'Zot Data: <input type="zot" name="zap"><br>'print '<input type="submit">'print ‘</form>’
The standard output (print statements) produce the HTTP
Response.
The output consists of HTTP headers followed
by the body of the document.
print 'Environment keys:'print ' 'for param in os.environ.keys(): print param, ":", os.environ[param]print ' '
print 'Data'count = 0for line in sys.stdin: count = count + 1 print line if count > 100: breakprint ‘</pre>’
Up Next...• If we wanted to write a real web application - we
would write a lot of string parsing code that looked at the environment variables and standard input
•We would spend a lot of time reading the HTTP documents to figure out the exact format of these strings
•This has already been done for us - this is provided as a framework on App Engine
http://code.google.com/appengine/docs/gettingstarted/usingwebapp.html
Summary•We introduced Cloud Computing - servers move
“into” the network cloud
•Google App Engine allows us to use the Google Cloud
•Common Gateway Interface - The ancient ways
•Writing simple low-level Python programs in AppEngine
•Using the AppEngine web framework (up next)