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Paolo Ciancarini
Architectures for software services
and cloud computing
Agenda
Rationale: the Service Economy Software as a Service (SaaS) Service oriented architectures The REST architectural style AJAX and mashups Cloud computing architectures
The Service Economy
Modern economies rely upon services This means that several companies offer support for
activities in the primary (agricolture) or secondary (industry of goods) sectors, or to other companies offering services themselves
A service company is usually independent (not owned) from other companies and their services; however in several cases they should cooperate or at least be coordinated in some way
From Products to Services Our society is shaped by the forces of
Specialization Standardization Scalability
It is now mostly “service” oriented Transportation Telecommunication Retail Healthcare Financial services Education and training …
Attributes of physical services A service is not owned by its user (compare with product) Well defined, easy-to-use, standardized interface
New services can be offered by combining existing services (almost) always available but idle until requests come “Provision-able” (used by someone only when necessary,
then reassigned to someone else) Easily accessible and usable readily
no “integration” required Self-contained : no visible dependencies to other services
Coarse grain Independent of consumer context
but a service can have a context Quantifiable quality of service
Do not compete on “What” but “How”
Example: mail Customers use mail everywhere Interfaces: PostOffice, Mail Box, stamp, postman Apparently no relationship with other services (eg.
Transportation, payments) Quality of service: price, delivery time, lost
messages
Nation % WW Labor
% A
% G
% S
25 yr % delta S
China 21.0 50 15 35 191
India 17.0 60 17 23 28
U.S. 4.8 3 27 70 21
Indonesia 3.9 45 16 39 35
Brazil 3.0 23 24 53 20
Russia 2.5 12 23 65 38
Japan 2.4 5 25 70 40
Nigeria 2.2 70 10 20 30
Banglad. 2.2 63 11 26 30
Germany 1.4 3 33 64 44
Top Ten Nations by Labor Force Size (about 60% of world labor in just 10 nations)
A = Agriculture, G = Goods, S = Services
>50% (S) services, >33% (S) services
2008
(S) Services: Value from enhancing the
capabilities of things (customizing, distributing, etc.) and interactions between things
The global service economy
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1810 1835 1860 1885 1910 1935 1960 1985 2010
China
United States
What is meant by Service?
In economics and marketing, a service is the intangible equivalent of an economic good. Service provision is an economic activity where the buyer does not generally, except by exclusive contract, obtain exclusive ownership of the thing purchased (Wikipedia, 2010)
A service is a “provider to client” interaction that creates and captures value while sharing the risks of the interactions
Services are the application of specialized competences (skills and knowledge) through deeds, processes, and performances for the benefit of another entity or the entity itself (Vargo & Lusch, 2004a)
Services are value that can be rented (in the broad sense) by the application of some process that the renter (client) participates in. This contrasts with goods, whose value (once purchased) is owned by the customer (Lovelock & Gummesson, 2004)
What is a Service (1)
Merriam-Webster
A facility supplying some public demand
the work performed by one that offers help, use, or benefit
What is a Service (2) In economics and marketing, a
service is a non-material equivalent of a good
Service composition is managed by service providers who have to offer or provision more complex services
The service-good spectrum shows that most services include some goods, and also that most goods involve some service
Example: restaurant
en.wikipedia.org/wiki/Service
Discussion Is software a good or a service?
11
Software-as-a-Service (SaaS) 1990: Web 0.9 (Tim Berners-Lee) 1995: Web 1.0 (some dynamic content, Netscape) 1997: Services (Google, e-commerce...) 1999: LoudCLoud (first infrastructure for SaaS) 2000: Web 2.0 (rich UI's, social computing) 2004: SaaS & SOA (Google Maps, Amazon S3...) 2008: Cloud Computing (pay as you go)
12
Software as a service Service: the non-material equivalent of a good Software is a service at heart, albeit an automated one, but
it is sold much like a manufactured good. Customers have to pay large sums of money up front, bear much of the risk that a program may not work as promised, and cannot readily switch vendors.
The Economist, 2003
Software-as-a-Service (SaaS) Definition of SaaS: Internet-based deployment (for access
and management) of commercially available software Service managed from “central” locations enabling
customers to access applications remotely via web Delivery: one-to-many model (single instance, multi-tenant
architecture) including architecture, pricing, partnering, and management characteristics
Centralized updating, which obviates the need for end-users to download patches and upgrades
Frequent integration into a larger network of communicating software—either as part of a mashup or a plugin to a platform as a service
14
Software as a service An operating system service?
Program execution, file management
A Software Service? Messaging Service Log Service Peer to peer distribution Search engine
A Business Service? Customer service Bidding service
Software services: a multidisciplinary problem
Business Issues
Service Oriented Architecture
Solutions Realized on an Infrastructure
Operational Issues
Functional Issues
• Industry policies • Industry imperatives • Business priorities
• Functionality expressed as Services
• Map to Business Processes • Based on standards
• Model Driven Development • Middleware and Software • Technology Platforms &
Frameworks • Network & Hardware
Business Model
Dimensions of Sw Engineering for Services
Software Construction
Distributed Computing
CORBA, J2EE
DCE
WS, ebXML
Application Model Mainframe
Client/Server
Web Apps
SAP, Oracle…
SalesForce.com
Solutions Computing Model
Structured Programming
Object Orientation
Middleware
MQ
EAI, B2B
BPM
RUP XP
MDD
Service Orientation
Methodologies
Portals
SOC and SOA
Service Oriented Computing is a distributed programming paradigm for business applications supporting complex enterprises
Service Oriented Architectures are systems of services producers and service consumers
Mostly made of independent software systems able to be dynamically integrated
SOA SOA = Service Oriented Architecture SOA is a recent term, but in the past have been
built many systems that today we could call SOAs. Example: the Web
The essence of a SOA lies in independent services interconnected by messages
On the Web, a specific SOA technology is Web Services (W3C)
20
OMG Standards for SOA http://www.omg.org/attachments/pdf/OMG-and-the-SOA.pdf
Interfaces defined by enterprise context
Data Data DataData
ServersMainframes MainframesServers
BPMN
UML
BPDM
SBVR
ODM UML
RAS
J2EE UML Profile
CORBA UML Profile
CWM/IMMKDM
BusinessProcess
BusinessServices
Task definition
Task implementation
Components
OperationalResources
Interfaces defined by enterprise semantics and requirements
Typical topics in SOA Model, design, and implement a SOA Create an agile, reusable SOA Automate business processes by mapping to the
architectural model Orchestrate services and execute processes with the
Business Process Execution Language (BPEL) Achieve interoperability within a SOA using proven
standards and best practices Secure and govern an enterprise SOA
Standardizing bodies for SOAs W3C (1994) OASIS (1993), consortium of former GML
providers, deals with applications using XML OMG (1989) WS-I (2002), promotes interoperability among the
stack of Web Services specifications"
Elements of SOA Design
Business Modeling Service Oriented Architectural Modeling and Design Model Driven assumptions (loose coupling) Distributed objects and MOM (Message Oriented
Middleware) for component-based sw systems
Business modeling
25
http://www.ibm.com/developerworks/rational/library/360.html
Service oriented modeling and architecting
26
Model driven SOA design
27 www.theenterprisearchitect.eu/archive/2009/06/03/a-framework-for-model-driven-soa
Services and SOAs A service is a program interacting via message
exchanges On Web all messages and service descriptions are
written in XML A SOA is a set of deployed services cooperating
in a given task Adapt to new services after deployment
SOA Concepts
Edge
Message Exchange Pattern
describe
Operational Requirements
enforce State
manage Service
Expose itself using
Messages
Process/Create
direction & types of Contracts
bound by
contain Schemas define structure of
governed by
Policies
implement
SOA Reference Architecture D
ata Architecture and B
usiness Intelligence
QoS, Security, M
anagement, and
Monitoring Infrastructure Service
Integration (Enterprise Service Bus A
pproach)
consumers
business processes process choreography
services atomic and composite
service components
operational systems
Service Consum
er Service Provider
AJAX Portlets WSRP B2B Other
OO Application
Custom Application
Packaged Application
Governance
Main SOA Standards BPEL (Business Process Execution Language): a standard for assembling sets
of discrete services into an end-to-end business process J2EE: the Java Platform, Enterprise Edition, with APIs for deploying and
managing Web services JSR 168: standard for portal and portlet interoperability JSR 181: an API for Web services metadata annotation SOAP (Simple Object Access Protocol): a W3C-approved standard for
exchanging information among applications UDDI (Universal Description, Discovery, and Integration): an OASIS-approved
standard specification for defining Web service registries WS-I (Web Services Interoperability): an open industry organization promoting
Web services interoperability across platforms, operating systems, and languages
WS-Reliability (Web Services Reliability): a SOAP-based protocol for exchanging SOAP messages, with delivery and message-ordering guarantees
WS-Security (Web Services Security): a SOAP-based protocol that addresses data integrity, confidentiality, and authentication in Web services
WSDL (Web Service Description Language): a W3C-approved standard for using XML to define Web services
WSIF (Web Services Invocation Framework): an open source standard for specifying, in WSDL, EJB implementations for the Web server
WSRP (Web Services for Remote Portlets): an OASIS standard for integrating remote Web services into portals
XML (Extensible Markup Language): a data markup language for Web services
What is SOA? Use other services as RPC servers for your app Web 1.0: large sites organized this way internally
Yahoo!, Amazon, Google, …: external “Services” available, but complex: Doubleclick ads, Akamai
XML based Web Services msgs and descriptions Web 2.0: consumer-facing service API’s
Services: Google API, Google Analytics, Amazon CloudFront...
Platforms: Facebook, Google Maps, ... Mashups, e.g. housingmaps.com User-composable services, e.g. Yahoo Pipes
32
Amazon.com: Web 1.0 SOA ~50 “two-pizza” teams of
“developer/operators” ~10 operators
monitor the whole site page the resolvers on alarm
~1000 resolvers 10-15 per team, 1 on-call 24x7 monitor own service, fix problems
Over 140 code change commits/month Internal microcosm of service-oriented architecture
(as were Yahoo, Google, others)
web server web server web server
web server web server service A web server web server service B
web server web server service C
DB DB DB
P. Bodík et al., Advanced Tools for Operators at Amazon.com, Proc. ICAC 2005
SOA = RPC Transport: HTTP(S) Data interchange:
XML DTD (e.g., RSS) JSON (Javascript Object Notation)
Request protocol: SOAP (Simple Object Access Protocol) JSON-RPC
On the horizon: WebHooks (HTTP POST callback, for “push”)
34
JSON-RPC Open connection to designated port on server Send HTTP method & request URI, with MIME type of body set to application/json Then send request body: { "version": "1.1", "method": "confirmFruitPurchase", "id": "194521489", "params": [ [ "apple", "orange", "pear" ], 1.123 ] }
Response might be something like this: { "version": "1.1", "result": "done", "error": null, "id": "194521489" }
You have to handle substantially all errors 35
RSS
Request is a regular HTTP GET to a specified URL
<?xml version="1.0" encoding="UTF-8"?> <rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1"> <channel> <title>Altarena Playhouse Ticket Availability</title> <link>http://www.audience1st.com/altarena/store</link> <description>Altarena Ticket Availability</description> <item> <title>Sylvia - Friday, May 14, 8:00 PM – Buy now</title> <link>http://.../store?showdate_id=347</link> <guid permalink="false">http://.../store?ts=1271058414</guid> </item> <item> ... </item> </channel> </rss>
36
AJAX and SOA
AJAX: client server client makes (async) requests to HTTP server client-side JavaScript upcall receives reply and
decides what to do commonly, response includes XHTML/XML to update
page, or JavaScript to execute Doesn’t really make sense except in context of client
SOA: server server or client server one principal makes (sync or async) requests to an
HTTP server formerly, principal was a server running some app today, powerful JavaScript clients blur the line
37
Two ways to do it...
38
“Thin” browser
client
Web 2.0 app Craigslist.org
Google Maps “Fat” browser client
+ Client portability +/– Client performance (both app download &
JavaScript execution) + Availability of utility libraries for app development – Privacy/trustworthiness of aggregator app – Caching
REST (Representational State Transfer) style Architectural style:
Client-server, stateless, cache description of properties that made Web 1.0 successful
by constraining SOA interactions In context of SOA for Web 2.0
HTTP is transport; HTTP methods (get, put, etc.) are the only commands
URI names are a resource Client has resource has enough info to request
modification of the resource on server A cookie can encode part of transferred state
If your app is RESTful, it’s easy to “SOA”-ify 39
What is REST? REST is a term coined by Roy Fielding in his Ph.D
dissertation to describe an architectural style of networked software systems
"Representation State Transfer is intended to evoke an image of how a well-designed Web application behaves: a network of web pages (a virtual state-machine), where the user progresses through an application by selecting links (state transitions), resulting in the next page (representing the next state of the application) being transferred to the user and rendered for use."
http://www.ebuilt.com/fielding/pubs/dissertation/top.htm
Why is it called "Representation State Transfer"?
Resource Client http://www.boeing.com/aircraft/747
747.html
The Client references a Web resource using a URL. A representation of the resource is returned (in this case as an HTML document). The representation (e.g., Boeing747.html) places the client application in a state. The result of the client traversing a hyperlink 747.html is another resource is accessed. The new representation places the client application into yet another state. Thus, the client application changes (transfers) state with each resource representation --> Representation State Transfer!
Fuel requirements Maintenance
...
Motivation for REST
"The motivation for developing REST was to create an architectural model for how the Web should work,
such that it could serve as a framework for the Web protocol standards.
REST has been applied to describe the desired Web architecture, help identify existing problems, compare alternative solutions,
and ensure that protocol extensions would not violate the core constraints that make the Web successful."
- Roy Fielding
REST with HTTP examples HTTP GET! HTTP PUT! HTTP POST! HTTP DELETE!Collection URI, such as http://example.com/customers/257/orders
List the members of the collection, complete with their member URIs for further navigation"
Replace the entire collection with another collection"
Create a new entry in the collection. The ID created is usually included as part of the data returned by this operation."
delete the entire collection"
HTTP GET! HTTP PUT! HTTP POST! HTTP DELETE!Element URI, such as http://example.com/resources/7HOU57Y Retrieve a representation of the addressed member of the collection in an appropriate MIME type"
Update (or create) the addressed member of the collection"
Treats the addressed member as a collection in its own right and creates a new subordinate of it."
Delete the addressed member of the collection. """
43
Example: REST vs SOAP-based A company deploying 3 Web services to enable its
customers to: get a list of parts get detailed information about a particular part submit a Purchase Order (PO)
See the REST solution first, then the SOAP solution
44
The REST way of Implementing the Web Services
Response (HTML/XML doc)
Web
Ser
ver
HTTP GET request URL 1
HTTP response
Response (HTML/XML doc)
HTTP GET request URL 2
HTTP response
HTTP POST URL 3
HTTP response URL to submitted PO
PO (HTML/XML)
Parts List
Part
PO
Implementing the Web Service using SOAP
• Service: Get detailed information about a particular part – The client creates a SOAP document that specifies the procedure
desired, along with the part-id parameter.
<?xml version="1.0"?> <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <p:getPart xmlns:p="http://www.parts-depot.com"> <part-id>00345</part-id> </p:getPart> </soap:Body> </soap:Envelope>
Again, the client will HTTP POST this document to the SOAP server at: http://www.parts-depot.com/soap/servlet/messagerouter Note that this is the same URL as was used when requesting the parts list. The SOAP server peeks into this document to determine what procedure to invoke.
Implementing the Web Services using SOAP
Request (XML doc)
Response (XML doc)
Web
Ser
ver
SOAP envelope
HTTP POST URL 1
HTTP Response
getPartsList()
Request (XML doc)
Response (XML doc)
HTTP POST URL 1
HTTP Response getPart(id) SOAP Server
Note the use of the same URL (URL 1) for all transactions. The SOAP Server parses the SOAP message to determine which method to invoke.
All SOAP messages are sent using an HTTP POST.
PO (XML doc) HTTP POST
URL 1 submit(PO)
Response (XML doc) HTTP Response
A RESTful architecture for BPM
48
XML (eXtensible Markup Language) <?xml version="1.0" encoding="UTF-8"?> <book year="1967"> <title>The politics of experience</title> <author> <firstname>Ronald</firstname> <lastname>Laing</lastname> </author> </book>
Really a metalanguage for describing hierarchical, semistructured, schema-less data
XML Document Type Definition (DTD) specifies structural & content constraints on a particular document type
49
Value Attribute
Element Element
XML (eXtensible Markup Language) <?xml version="1.0" encoding="UTF-8"?> <book year="1967"> <title>The politics of experience</title> <author> <firstname>Ronald</firstname> <lastname>Laing</lastname> </author> </book>
Really a metalanguage for describing hierarchical, semistructured, schema-less data
XML Document Type Definition (DTD) specifies structural & content constraints on a particular document type
50
XHTML & CSS XHTML: a document conforming to a particular DTD
describing a hierarchical collection of HTML elements Variants: Strict, loose, transitional (for compatibility with deterioriating HTML
syntax 1990-95)
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
inline (headings, tables, lists...) embedded (images, video, Java applets, JavaScript code...) fill-in forms—text, radio/check buttons, dropdown menus...,
marshaling arguments into either URI or request body
CSS (Cascading Stylesheets) for presentation Strict XHML forbids presentational markup Idea: complete separation of appearance from structure
51
CSS Styles get visual styling applying selectors
<link rel="stylesheet" href="mystyles.css"/> <div class="pageFrame" id="pageHead">
<h1> Welcome, <span id="custName">Armando</span> </h1> </div>
In mystyles.css (static asset with MIME type text/css): div.pageFrame { background-image: url('/banner.gif'); } h1 { font-size: large; float: left; } #custName:hover { background-color: yellow; font-weight: bold; } Style properties include borders, background images, and layout
directives (floating, absolute positioning, min/max scaled sizes, etc.) Changing style properties has side effect of re-rendering e.g., change display or visibility property to show/hide elements
53
54
Dynamic content generation Most Web 1.0 (e-commerce) sites actually run a
program that generates the output Originally: templates with embedded code
“snippets” Eventually, embedded code became “tail that
wagged the dog” and moved out of the Web server Languages/frameworks evolved to capture
common tasks Perl, PHP, Python, Ruby on Rails, ASP, ASP.NET, Java
Servlet Pages, Java Beans/J2EE, ...
55
SaaS 3-tiers architecture
Common gateway interface (cgi): allows a Web server to run a program Server maps some URI’s to application names When the app is run, it gets the complete HTTP
request including headers “Arguments” embedded in URL with “&”
syntax or sent as request body (with POST) http://www.foo.com/search?term=white
%20rabbit&show=10&page=1 App generates the entire response
content (HTML? an image? some javascript?) HTTP headers & response code
Plug-in modules for Web servers allow long-running CGI programs & link to language interpreters
HTTP server
application
persistent storage
app server
storage
• Various frameworks have evolved to capture this structure!
56
SaaS 3-tiers deployment HTTP server (“web server”)
“fat” (e.g. Apache): support virtual hosts, plugins for multiple languages, URL rewriting, reverse proxying, ....
“thin” (nginx, thin, Tomcat, ...): bare-bones machinery to support one language/framework; no frills
Application server 1. separate server process, front-ended by a “thin” HTTP
server 2. or linked to an Apache worker via FastCGI or web server
plug-in: mod_perl, mod_php, mod_rails, ... Apache can spawn/quiesce/reap independent processes
Persistent storage Common RDBMS (MySQL, PostgreSQL, etc.) communicate w/app via proprietary or standardized
database “connector” (ODBC, JDBC, ...) Hence LAMP: Linux, Apache, MySQL, PHP/Perl
57
HTTP server
application
persistent storage
app server
storage
Frameworks Support for more languages: Apache modules
(mod_perl, mod_php, mod_rails ...) avoid spawning new process per request typically embed language interpreter in Apache
Support for common idioms like sessions Cookie management virtualize connection to database “dispatcher” interactions with front-end HTTP server
Early “templating systems” (e.g. PHP) vs. modern “full stack frameworks” (e.g. Rails)
58
Example: Rails, a Ruby-based MVC Framework
apache
your app
CGI or other dispatching
Relational Database
mysql or sqlite3
Ruby interpreter
firefox
tables
models/*.rb
controllers/*.rb Rails
routing
views/*.html.erb Rails
rendering
Model, View, Controller
Subclasses of ActiveRecord::Base
Subclasses of ActionView
Subclasses of ApplicationController
• Implemented almost entirely in Ruby • Distributed as a Ruby “gem” (collection of related libraries & tools) • Connectors for most popular databases
What’s new in Web 2.0? Primitive UI => Rich UI
enable “desktop-like” interactive Web apps enable browser as universal app platform on cell phones
“Mass customize” to consumer => Social computing tagging (Digg), collaborative filtering (Amazon reviews), etc. =>
primary value from users & their social networks write-heavy workloads (Web 1.0 was read-mostly) lots of short writes with hard-to-capture locality (hard to shard)
Libraries => Service-oriented architecture Integrate power of other sites with your own (e.g. mashups that
exploit Google Maps; Google Checkout shopping cart/payment) Pay-as-you-go democratization of “services are king” Focus on your core innovation
Buy & rack => Pay-as-you-go Cloud Computing
60
Rich Internet Apps (RIAs) Closing gap between desktop & Web
Highly responsive UI’s that don’t require server roundtrip per-action More flexible drawing/rendering facilities (e.g. sprite-based animation) Implies sophisticated client-side programmability Local storage, so can function when disconnected
early example: Google Docs + Google Gears include offline support, local storage, support for video, support for arbitrary
drawing, ... currently many technologies—Google Gears, Flash, MS
Silverlight... client interpreter must be embedded in browser (plugin, extension, etc.) typically has access to low-level browser state => new security issues N choices for framework * M browsers = N*M security headaches
proposed HTML5 may obsolete some of these
61
Rich UI with AJAX (Asynchronous Javascript and XML)
Web 1.0 GUI: click → page reload Web 2.0: click → page can update in place
also timer-based interactions, drag-and-drop, animations, etc.
How is this done? 1. Document Object Model (1998, W3C) represents
document as a hierarchy of elements 2. JavaScript (1995; now ECMAScript) makes DOM
available programmatically, allowing modification of page elements after page loaded
3. XMLHttpRequest (2000) allows async HTTP transactions decoupled from page reload
4. JavaScript libraries (jQuery, Prototype, script.aculo.us) encapsulate useful abstractions
62
DOM & JavaScript: Document = tree of objects
hierarchical object model representing HTML or XML doc
Exposed to JavaScript interpreter Inspect DOM element value/attribs Change value/attribs → redisplay or fetch new
content from server Every element can be given a unique ID JavaScript code can walk the DOM tree or select
specific nodes via provided methods
<input type="text" name="phone_number" id="phone_number"/>!<script type="text/javascript">! var phone = document.getElementById('phone_number');! phone.value='555-1212';! phone.disabled=true;! document.images[0].src="http://.../some_other_image.jpg";!</script>!
63
JavaScript
A browser-embedded scripting language OOP: classes, objects, first-class functions, closures dynamic: dynamic types, code generation at runtime JS code can be embedded inline into document...
<script type="text/javascript"> <!-- # protect older browsers calculate = function() { ... } // -->
</script>
...or referenced remotely: <script src="http://evil.com/Pwn.js"/>
Current page DOM available via window, document objects Handlers (callbacks) for UI & timer events can be attached to JS
code, either inline or by function name: onClick, onMouseOver,... Changing attributes/values of DOM elements has side-effects, e.g.:
<a href="#" onClick="this.innerHTML='Presto!'">Click me</a>
64
AJAX = Asynchronous Javascript and Xml
Recipe: attach JS handlers to events on DOM
objects in handler, inspect/modify DOM elements
and optionally do asynchronous HTTP request to server
register callback to receive server response response callback modified DOM using
server-provided info JavaScript as a target language
Google Web Toolkit (GWT): compile Java => emit JS Rails: runtime code generation ties app abstractions to JS
65
A browser is an application container
“Web apps” include animation, sound, 3D graphics, disconnection, responsive GUI... Browser =~ new OS: manage mutually-untrusting apps (sites)
66 Sour
ce: R
ober
t OʼC
alla
han
(Moz
illa.
org)
,! In
side
Fire
fox!
Social Computing
Web 1.0: add value via mass customization select content/presentation for you based on best guesses about
your interests resource: demographic/analytic data about you
Web 2.0: add value via connecting to social network vendor: your friends’ interests are a good indicator of your interests user: value added to existing content == how your friends interact
with it resource: your social network
From social networking site to social network as a way of structuring applications
67
Social Computing Amount of content “created” by each user small!
e.g., Digg article, rate video, play a Facebook game
but still creates lots of short random writes consider “Like” feature on Facebook social graphs naturally hard to partition (though would
love to see a paper about this from FB) question for Web 2.0 developers is not whether
social computing is part of your app, but how later we will discuss technical architecture of
“connecting” an app to social networks
68
Facebook plug-in apps
• Facebook platform (“Facebook Connect”)!
69
AJAX
Facebook.com! Your app!2.!3.!
FB data!FBQL!
4. html
1.
SOA
3. Your app! Facebook.com!
FB data!
html+ xfbml
1.
4.
2 (opt.). REST!
èREST via JavaScript & XFBML!
ç HTML IFRAME w/FB content!
Google Maps
Your app embeds Javascript-heavy client code (provided by Google) client-side functionality: clear/draw overlays, etc. server-side functionality: fetch new map, rescale, geocoding
Attach callbacks (handled by your app) to UI actions Result of callback can trigger additional calls to Google
Maps code, which in turn contact GMaps servers
html+ js
Your app
Google Maps
1. 2.
3. 4.
70
Mashups: housingmaps.com
71
Scaling via Replication
The “most general” deployment scenario for a 3 tier Web application Many Web servers possibly including static-asset servers L4/L7 load balancers distribute load among them
Caches and reverse proxies remember previously-computed content whole page caching page fragment caching, query caching Apache in reverse-proxy mode, or
memcached process(es) addressed by app server
Integration of caching with application logic varies by framework
WS WS …
$ $ …
LB LB …
App App
DB DB?
…
the Internets
Asset Svr
72
“Scale makes availability affordable”
Goal: interchangeability (send any user request to any available server) each server handles 1/N load affinity can be used to “soft-pin” users to
particular servers requires good support for session state
abstraction in app framework lose 1 server => lose 1/N capacity
Load Balancers have logic to detect failed servers & remove from rotation until they are resurrected
73
WS WS …
$ $ …
LB LB …
App App
DB DB?
…
the Internets
Asset Svr
Asset Servers For serving static assets (images, sound clips,
CSS, etc.) Separate Web server process, configuration
optimized for fast static file serving Web 2.0: use Amazon S3 (blob store) or
CloudFront (CDN) helps to have good asset-server abstraction in app
framework
74
Deployment scenarios (& approximate pricing)
Buy/rack/install/configure it yourself...that’s so Web 1.0 Shared hosting ($3/month)
turnkey support for popular frameworks, hosted versions of popular building blocks (e.g. MySQL)
highly variable performance, multitenant per machine Virtual private host ($10/month)
better isolation and security through virtualization substantially more administration
“Framework VM” or “curated” environments (Heroku, Google AppEngine, Force.com) – pricing varies hosted extensions: memcached, profiling, etc. integration of 3rd party hosted services, e.g. Amazon S3 backup
Cloud Computing
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Pay-as-you-go Cloud Computing
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Amazon Elastic Compute Cloud (EC2) “Compute units” $0.085/hr & up
1 CU ≈ 1.0-1.2 GHz 2007 AMD Opteron/Xeon core
N No up-front cost, no contract, no minimum storage (~0.15/GB/month) network (~0.10-0.15/GB external; 0.00 internal) Everything virtualized, even concept of
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“Instances”! Platform! Cores! Memory! Disk!Small - $0.085 / hr" 32-bit" 1" 1.7 GB" 160 GB"
Large - $0.34/ hr" 64-bit" 4" 7.5 GB" 850 GB – 2 spindles"XLarge - $0.68/ hr" 64-bit" 8" 15.0 GB" 1690 GB – 3 spindles"
Options....extra memory, extra CPU, extra disk, ..."
Unused resources
Cloud Economics: user side
Cloud Computing: User side" Static provisioning for peak "
- wasteful, but necessary for SLA"
“Statically provisioned” data center
“Virtual” data center in the cloud
Demand
Capacity
Time
Mac
hine
s
Demand
Capacity
Time
$
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Unused resources
Cloud Economics 101
Cloud Computing Provider: Could save energy"
“Statically provisioned” data center
Real data center in the cloud
Demand
Capacity
Time
Mac
hine
s
Demand
Capacity
Time
Ener
gy
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Unused resources
Risk of Overprovisioning
Underutilization results if “peak” predictions are too optimistic"
Static data center
Demand
Capacity
Time
Res
ourc
es
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“Risk Transfer” to Cloud
“Cost associativity” from linear pricing: 1,000 CPUs for 1 hour same price as 1 CPUs for 1,000 hours (@$0.10/hour) Washington Post converted Hillary Clinton’s travel documents to
post on WWW <1 day after released Lab graduate students demonstrate improved Hadoop (batch job)
scheduler—on 1,000 servers
Major enabler for SaaS startups Animoto traffic doubled every 12 hours for 3 days when released as
Facebook plug-in Scaled from 50 to >3500 servers ...then scaled back down
Goal: fix any transient problem by adding/removing nodes Single-node performance becomes much less important
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Classifying Clouds for Web 2.0
Instruction Set VM (Amazon EC2) Managed runtime VM (Microsoft Azure) Curated “IDE-as-a-service” (Heroku) Platform as service (Google AppEngine, Force.com)
flexibility/portability vs. built-in functionality
EC2 Azure Force.com
Lower-level, Less managed
Higher-level, More managed,
more value-added SW
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Heroku, AppEngine
Joyent
Deployment “Deployment-as-a-service” increasingly common
monthly pay-as-you-go curated environment (Heroku) hourly pay-as-you-go cloud computing (EC2) hybrid: overflow from fixed capacity to elastic capacity Remember administration costs when comparing!
Good framework can help at deployment time Separate abstractions for different types of state: session state,
asset server, caching, database ORM – natural fit for social computing, and abstracts away from
SQL (vs Web 1.0 PHP, e.g.) REST – encourages you to make your app RESTful from start, so
that “SOA”-ifying it is trivial
Scaling structured storage: open challenge
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Cloud Computing CC makes it possible to obtain results on 1000’s of
servers Es. BOOM (declarative cloud programming)
boom.cs.berkeley.edu Eucalyptus www.eucalyptus.com makes hybrid
cloud computing reasonably practical Run small experiments locally, then “scale up” to cloud
for results Why aren’t you using cloud computing yet?
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Example: Facebook Facebook has 2 datacenters, 1 per coast
reads spread across both writes only to W. Coast; periodically (~10 minutes)
replicated to E. Coast >2000 MySQL servers, >25TB RAM for memcached
Challenge: inconsistency due to stale data I change status message => Friends on East Coast
datacenter do not see my change for 10 min What if E.Coast person changes his own status??
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Source: “How Facebook Works”,Technology Review, Jul/Aug 2008
Facebook cloud servers
SCADS: Scalable, Consistency-Adjustable Data Storage
Most popular websites follow the same pattern Outgrow initial prototype (on MySQL) due to scale Build large, complicated ad-hoc systems to deal with
scaling limitations as they arise Want Scale Independence as new users join:
No changes to application Cost per user & request latency don’t increase
Key Innovations 1. Performance-{safe,insightful} query language 2. Declarative performance/consistency tradeoffs 3. Automatic scale up & down using machine learning
M. Armbrust et al., SCADS: Scalable Consistency-Adjustable Data Storage for Interactive Applications. Proc. CIDR 2009!M. Armbrust et al., PIQL: A Performance-Insightful Query Language. Proc. SOCC 2010. !
Understanding workload spikes death of Michael Jackson: 23% of tweets, 15% of Wikipedia
traffic...how to understand/synthesize spikes? characterized 5 real spikes large differences in many characteristics: steepness, magnitude, #
data hotspots, … spike synthesis tool generates realistic workload with few
parameters using statistically sound model Cloud computing offers alternative to overprovisioning?
stateful
system
policy
ac/ons workload
model Explora/on of performance [ACDC ’09]
Policy simulator [HotCloud ’09]
Resource alloca/on for stateful systems
P. Bodik et al., Characterizing, modeling, and generating workload spikes for stateful services, SOCC 2010!P. Bodik et al., Statistical machine learning makes automatic control practical for Internet datacenters, HotCloud '09!
P. Bodik et al., Automatic exploration of datacenter performance regimes, ACDC '09 !!!!
Browsers are more and more fat Performance, security and GUI choke point
Cookie management, JavaScript, XSS attacks CSS layout, side-effects of DOM manipulation AJAX: document can change anytime after loading RIA frameworks/plugins: Flash, HTML 5, Silverlight Device variation: new twist due to power limits See http://www.google.com/googlebooks/chrome for a
great fun-to-read description in comic-book form
Bring “desktop-quality” browsing to mobile tel Enabled by 4G networks, better output devices Parsing, rendering, scripting are all potential bottlenecks
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Parallelizing the Browser (R.Bodík et al.)
New algorithms for CSS, layout, rendering, up to 80X speedup on popular web sites
Constraint-based browser programming language unifies layout, rendering, scripting
0 5
10 15 20 25 30 35 40 45 50
1 2 3 4 5 6 7 8
Spee
dup
Hardware Contexts
Slashdot (CSS Selectors)
84ms
2ms
Try it yourself 1. Download & install RoR (rubyonrails.org)
A good intro book: Simply Rails 2 by Patrick Lenz
2. Signup for a free Heroku.com trial account 3. Install various useful “Ruby gems” (libraries):
gem install heroku cucumber-rails rspec-rails
4. Create app skeleton: rails mynewapp ; git commit –m “new app” mynewapp heroku create mynewapp
5. Start writing user stories and track your progress (PivotalTracker.com)
6. When ready to deploy on Heroku: git push heroku master
More resources: http://radlab.cs.berkeley.edu > Courses
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Summary New ecosystem: changes software process,
deployment process, interdependencies of DADO (everything-as-a-service)
Web 2.0 tools have reached a new plateau of productivity
Gap closing between “web app” user experience vs. desktop app
New interesting research problems
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Self test Which are the consequences of defining software a
service insted of a good? What are the main original features of the REST
style? Which software architectural issues are typical of
social software? What are the economic basis of cloud computing?
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References www.armandofox.com/geek/teaching/ radlab.cs.berkeley.edu msdn.microsoft.com/en-us/library/aa479069.aspx
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Questions?
