Docstoc

Web Servers SI540

Document Sample
Web Servers SI540 Powered By Docstoc
					SI540 Understanding Networked Computing




           Scalability


Nobody uses that site anymore;
       it’s too popular
         Learning Objectives

• Understand scalable provisioning
  › Caching
  › Load balancing




                                     2
                  Scalability

• Goal: handle more users with more hardware
  › But without architecture changes
• Architecture must have variable number of
  identical components
  › Parallel processing to handle higher load
  › Load balancing among components
• Avoid bottlenecks
  › Components that may delay work of others if
    overloaded


                                                  3
            Scalable Web Services

• Replication                 • Load balancing
   › Caches distributed          › Switch acts as
     around network                intermediary
                                    › Looks inside IP
   › Replicated Web servers           packets
   › Replicated database                › TCP port (80)
     servers                            › Path in HTTP GET
                                          request
                                    › Routes traffic
                                      accordingly




 Internet    Load-balancing   Replicated    Replicated DB
                Switch        Web Servers     Servers        4
          Caching and Distributed Delivery
          Sites: Content Delivery Services


                                               Web
                                               Server

  Web
browser
                          Internet
                                 •Web page has img links to
                                 Akamai URLs
                 Akamai          •DNS for Akamai resolves
                 Edge            to IP address of an edge
                 Server          server “near” you        5
    Load Balancing Techniques

• Pick a server
  › at random
  › based on average load (or response time)
  › based on current load (or response time)
• How often?
  › Choose once, connect many
  › Choose every time




                                               6
    Load Balancing Techniques

• Who picks
  › Client
     › If you go to www.netscape.com using Netscape’s
       browser, it will automatically direct you to
       www[random server #].netscape.com (e.g.,
       www5.netscape.com)
  › Intermediary (must process faster than server!)
     › DNS server (e.g., Akamai)
     › Load balancing switch (sometimes called a reverse
       proxy)
        › Or server running balancing software (e.g., Network
          Dispatcher)
     › Web servers via redirections

                                                                7
         Load Balancing Techniques
DNS               Web server

Client   DNS      Web server

                  Web server
                                  Load balancing switch
                                             Web server
                                 Load
               Client   DNS    Balancing     Web server
                                Switch
                                             Web server
Web servers       Web server


Client   DNS      Web server


                  Web server
                                                      8
    A View from the Real World

• Rob Malda
• Editor, SlashDot.org




                                 9

				
DOCUMENT INFO