Under the Hood of a Commercial Web Site

Information Technology I Under the hood of a commercial Web Site � Issues � Typical Site Architecture � Case Study: Travelocity The story so far… Web Server Web browser Internet CGI/ASP script Static content Web Site Database Information Technology I Travelocity Architecture BROWSER INT ERN ET FrontFront- end Netscape WEB SERVER Hosted by: Sabre Netscape API Shared Object PlugIn Live CAS sgi content transaction TP Middleware Vignette Story Server 4 CMS BackBack-end Content DataBase Sun TCL BUSINESS SERVICES STB OFEP Vignette UPCI PROFILE DataBase Oracle SABRE Issues for building mission-critical eCommerce sites � Content management � � Security � � � Ensure the computer services remain available to users in the face of partial failures Accuracy � � Physical security Access control Availability/Fault Tolerance � � Ensure that content development is done in a streamlined and orderly fashion Ensure that multi-user access and system crashes leave data in an accurate state Scalability � Ensure that response time remains acceptable as site traffic grows Information Technology I Building mission-critical eCommerce sites: Summary of Technologies � Content management � � Security � � � Replication Accuracy � � Physical security: Hosting Access control: Firewalls Availability/Fault Tolerance � � Content Management Software Transaction Processing Scalability � � � Replication Load Balancing Web Caching Issue #1: Large-scale content development � Large number of authors contributing site content � Diverse types of content (e.g., image, video, and other media files) � Need for regular content posting and replacement (i.e., weekly sales promotions) � Often one or more approvals are required before content is posted � Some content needs to be personalized or tailored to match the needs and interests of a site visitor Information Technology I Additional issues � Often support for multiple languages and time zones is required � Content presentation must consistently conform to branding and appearance standards � Version archiving and an audit trail � Content must be viewable across a variety of browsing devices, not just PCs Example: Content update workflow � Automatic support for content management workflows Information Technology I Solution: Content management systems � Still a fledgling application category � � Relatively small adoption from site developers � � � More than 50% of sites use manual methods Market leader (Vignette) only has 8% of market!!! Hefty price tag � � Lots of Web authoring tools claim to be but aren’t! Vignette comes to more than $0.5M Lots of growth potential, but also room for better products Representative Vendors � CardoNet � Interwoven � OnDisplay � Poet � Versifi � Vignette Information Technology I Issue #2: Network and Physical Security What a firewall does � Hides the address of the network by making it appear that all transmissions originate from the firewall. � Passes outgoing traffic without screening, while hiding the network address. � Blocks all data not specifically requested by a legitimate user of the network. � Screens data for source and destination address so you receive data from only trusted locations like people on your approved guest list. � Screens the contents of data packets for known hacker attacks Information Technology I Types of firewalls � Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. � Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. � Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses Web Hosting � Ensure 24x7 site operation � Provide access to network bandwidth � Provide physical site security Information Technology I Self-manage or Host? � Hosting services are on the rise � � � Concentrated technology expertise Scalability and performance issues Security issues � Hosters are an uneven lot � Hosting is not a commodity The various flavors of hosting � Simple hosting � � Collocation hosting � � Examples: Frontier GlobalCenter, Sprint, UUNET Managed hosting � � Examples: Sprint, UUNET Examples: GTE, UUNET, IBM, Qwest Full-service hosting � Examples: IBM, Qwest Information Technology I There is no single right answer � Select level of hosting based on what kind of company you are � eCommerce pioneer � collocation hosting � basic eCommerce presence � simple hosting � some in-house expertise � managed hosting � Yahoo, Amazon Century 21 Land’sEnd, Vanguard little in-house expertise � full-service hosting - Amtrak, General Motors Issue #3: Ensuring Availability and Fault Tolerance � Why do computers crash? � � � � � Hardware errors Operating system errors Application errors Human errors Use redundancy to restore normal operation after crashes � � Data redundancy Active Replication Information Technology I Data Replication � Keep several copies of same data (replicas) � If one server is down, query next server � Can improve response when load is heavy � Problem: How to synchronize replicas? Active Replication � Establish redundant copies of vital programs and servers � � � Every message is processed by all group members � � process groups every group member operates on its own replica members remain in mutually consistent states If one member fails, other members can still respond Information Technology I How can we do even better? Issue #4: System Crashes might corrupt data n Transfer money from savings to checking - x=sav; sav = x+1 - w=chk; chk = w -1 n What happens if system crashes in the middle - x=sav; sav = x+1 - SYSTEM CRASH n Need to have a way to undo the effects of partially completed logical operations Information Technology I Solution: Transaction Model � Transaction: a process that possibly changes the database state � � � � Self-contained, indivisible set of accesses to the database May involve several reads and writes All-or-nothing execution Example: Transfer money is a single transaction - x=sav; sav = x+1; w=chk; chk = w -1 Using Transactions for Crash Recovery � Transactions are atomic (indivisible) � � � Either executes completely or not at all Any transaction that has not yet issued any writes may restart without causing any damage. Once a transaction starts writing, it should do all of its writes � Even if it crashes in the middle Transactions are durable � If the transaction is “committed” (starts writing) - It should finish, even if machine crashes partway through Information Technology I Implementation: DO-UNDO-REDO Log Keep a log of all database writes ON DISK � � transaction id; data item; new value � But don't write to the database yet - (Tj; x=25) (Ti; y=56) At the end of transaction execution � � � � � Add "commit " to the log Do all the writes to the database Add "complete " to the log Now it’s OK to release the locks Restart after a crash by redoing the log � � Any write for a committed but uncompleted transaction gets written again � Any write for a non-committed or completed transaction is ignored - What if the value was already written? Distributed Transactions � Distributed transaction may write data to several sites � � � Want to write all data or cancel the transaction � � � � Transfer money between accounts on separate computers Update several copies of a database Transaction Manager program may crash Data sites may crash Network may temporarily stop sending messages Needs more complicated protocols � out of the scope of this class Information Technology I Issue #5 Scalability: Why you should care � "... the No.1 reason that customers got fed up and took their business elsewhere was technical problems, including unacceptably slow response times." - � Fortune magazine, November 8, 2001 "...28% of Netizens that encountered glitches, left the site never to return" - Business Week, November 1, 2001 Technological Alternatives � Local load balancer � Site mirroring � Network caching � Content routing Information Technology I Load balancing solutions Companies: Cisco, HydraWeb Distributes client requests among replicated servers Web Server A Load balancer Web Server B Web browser Internet Local Load balancer Replicated Web servers Network caching solutions Companies: Inktomi, CacheFlow Web Server Web browser Routers store copies of most frequently accessed Web pages and can deliver them directly (instead of passing all requests on to the server) Internet Information Technology I Intelligent content routing Web Site Logo “Rich content” “Rich content” “Rich content” Menu Bar Text “Rich content” Main page (Text) 31 Intelligent content routing Companies: Akamai, Sandpiper Information Technology I Akamai Current Network Building mission-critical eCommerce sites: Summary of Technologies � Content management � � Security � � � Server Replication Accuracy � � Physical security: Hosting Access control: Firewalls Availability � � Content Management Software Transaction Processing Scalability � � � Replication Load Balancing Web Caching Information Technology I A Three Layer Website Architecture BROWSER INT ERN ET Firewall Load Balancer Front-end Web Server Session management software Database intelligence Middleware Inventory Database Back-end Web interface/ Manage page hits Web Server Content DataBase Profile DataBase Customer and session Management Transacion and requests management Read/ Store data Travelocity Architecture BROWSER INT ERN ET FrontFront- end Netscape WEB SERVER Hosted by: Sabre Netscape API Shared Object PlugIn Live CAS sgi content transaction TP Middleware Vignette Story Server 4 CMS BackBack-end Content DataBase Sun TCL BUSINESS SERVICES STB OFEP Vignette SABRE UPCI PROFILE DataBase Oracle