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APACHE WEBSERVER

Learn about Apache web server, different components of system architecture, client-server interaction, and accessing web servers. Understand the features of Apache web server such as scalability, reliability, and stability.

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APACHE WEBSERVER

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  1. APACHE WEBSERVER

  2. Introduction • Web server • Responds to client requests by providing resources • URI (Uniform Resource Identifier) • Web server and client communicate with platform-independent Hypertext Transfer Protocol (HTTP)

  3. WEB SERVERS

  4. HTTP Request Types • Request methods • get • post • Retrieve and send client form data to Web server • Post data to a server-side form handler

  5. System Architecture • Multi-tier application (n-tier application) • Information tier (data or bottom tier) • Maintains data for the application • Stores data in a relational database management system (RDBMS) • Middle tier • Implements business logic and presentation logic • Control interactions between application clients and application data • Client tier (top tier) • Application’s user interface • Users interact directly with the application through the client tier

  6. Client-Side Scripting versus Server-Side Scripting • Client-side scripts • Validate user input • Reduce requests needed to be passed to server • Access browser • Enhance Web pages with DHTML, ActiveX controls, and applets • Server-side scripts • Executed on server • Generate custom response for clients • Wide range of programmatic capabilities • Access to server-side software that extends server functionality

  7. Accessing Web Servers • Request documents from Web servers • Host names • Local Web servers • Access through machine name or localhost • Remote Web servers • Access through machine name • Domain name or Internet Protocol (IP) address • Domain name server (DNS) • Computer that maintains a database of host names and their corresponding IP address

  8. What makes a good Web Server? • Correctness • Reliability • Scalability • Stability • Speed

  9. Correctness • Does it conform to the HTTP specification? • Does it work with every browser? • Does it handle erroneous input gracefully?

  10. Reliability • Can you sleep at night? • Are you being paged during dinner? • It is an appliance?

  11. Scalability • Does it handle nominal load? • Have you been Slashdotted? • And did you survive? • What is your peak load?

  12. Speed (Latency) • Does it feel fast? • Do pages snap in quickly? • Do users often reload pages?

  13. Apache the General Purpose Webserver Apache developers strive forcorrectness first, andspeed second.

  14. Apache Web Server • Currently the most popular Web server • Stability • Efficiency • Portability • Open-source

  15. Apache 1.3 • Fast enough for most sites • Particularly on 1 and 2 CPU systems.

  16. Apache 2.0 • Adds more features • filters • threads • portability (has excellent Windows support) • Scales to much higher loads.

  17. Apache HTTP ServerArchitecture Overview

  18. Classic “Prefork” Model • Apache 1.3, and • Apache 2.0 Prefork • Many Children • Each child handles one connection at a time. Parent Child Child Child … (100s)

  19. Multithreaded “Worker” Model • Apache 2.0 Worker • Few Children • Each child handles many concurrent connections. Parent Child Child Child … (10s) 10s of threads

  20. Dynamic Content: Modules • Extensive API • Pluggable Interface • Dynamic or Static Linkage

  21. In-process Modules • Run from inside the httpd process • CGI (mod_cgi) • mod_perl • mod_php • mod_python • mod_tcl

  22. Out-of-process Modules • Processing happens outside of httpd (eg. Application Server) • Tomcat • mod_jk/jk2, mod_jserv • mod_proxy • mod_jrun Parent Tomcat Child Child Child

  23. Architecture: The Big Picture Parent 100s of threads 10s of threads Tomcat Child Child Child … (10s) DB mod_jk mod_rewrite mod_php mod_perl

  24. “HTTP” • HyperText Transfer Protocol A network protocol used to communicate between web servers and web clients (eg. a Web Browser).

  25. “Request” and “Response” Request • Web browsers request pages and web servers respond with the result. • Multi-Processing Module • An MPM defines how the server will receive and manage incoming requests. • Allows OS-specific optimizations. • Allows vastly different server models (eg. threaded vs. multiprocess). Response Web Browser(Mosaic) Web Server (Apache)

  26. “Client” • Single HTTP connection (eg. web browser). • Note that many web browsers open up multiple connections. Apache considers each connection uniquely. Web Browser(Mosaic) Web Server (Apache)

  27. “Thread” • In multi-threaded MPMs (eg. Worker). • Each thread handles a single connection. • Allows Children to handle many connections at once.

  28. Apache Configuration httpd.conf walkthrough

  29. Prefork MPM • Apache 1.3 and Apache 2.0 Prefork • Each child handles one connection at a time • Many children • High memory requirements • “You’ll run out of memory before CPU”

  30. Prefork Directives (Apache 2.0) • StartServers- The number of child processes to create at start-time • MinSpareServers-The minimum number of idle children to have at any time • MaxSpareServers-The maximum number of idle children to have at any time • MaxClients-The maximum number of concurrent client connections to allow at any time • MaxRequestsPerChild-The maximum number of requests that each child is allowed to serve before it must terminate and be replaced. Useful for starting with a clean slate every once in awhile, and particular useful for buggy 3rd party modules that leak precious system resources

  31. Worker MPM • Apache 2.0 and later • Multithreaded within each child • Dramatically reduced memory footprint • Only a few children (fewer than prefork)

  32. Worker Directives • MinSpareThreads • MaxSpareThreads • ThreadsPerChild • MaxClients • MaxRequestsPerChild

  33. KeepAlive Requests • Persistent connections • Multiple requests over one TCP socket • Directives: • KeepAlive • MaxKeepAliveRequests • KeepAliveTimeout

  34. Apache 1.3 and 2.0Performance Characteristics Multi-process, Multi-threaded, or Both?

  35. Prefork • High memory usage • Highly tolerant of faulty modules • Highly tolerant of crashing children • Fast • Well-suited for 1 and 2-CPU systems • Tried-and-tested model from Apache 1.3 • “You’ll run out of memory before CPU.”

  36. Worker • Low to moderate memory usage • Moderately tolerant to faulty modules • Faulty threads can affect all threads in child • Highly-scalable • Well-suited for multiple processors • Requires a mature threading library(Solaris, AIX, Linux 2.6 and others work well) • Memory is no longer the bottleneck.

  37. Benchmarking Metrics • What are we interested in testing? • Recall that we want our web server to be • Correct • Reliable • Scalable • Stable • Fast

  38. Benchmarking Metrics: Correctness • No errors • No data corruption • Protocol compliant • Should not be an everyday concern for admins

  39. Benchmarking Metrics: Reliability • MTBF - Mean Time Between Failures • Difficult to measure programmatically • Easy to judge subjectively

  40. Benchmarking Metrics: Scalability • Predicted concurrency • Maximum concurrent connections • Requests per Second (rps) • Concurrent Users

  41. Benchmarking Metrics:Stability • Consistency, Predictability • Errors per Thousand • Correctness under Stress • Never returns invalid information • Common problem with custom web-apps • Works well with 10 users, but chokes on 1000.

  42. Benchmarking Metrics:Speed • Requests per Second (rps) • Latency • time until connected • time to first byte • time to last byte • time to close • Easy to test with current tools • Highly related to Scalability/Concurrency

  43. Web Resources • www.microsoft.com/msdownload/ntoptionpack/askwiz.asp • www.w3.org/Protocols • www.apache.org • httpd.apache.org • httpd.apache.org/docs-2.0 • www.apacheweek.com • linuxtoday.com/stories/18780.html • www.iisanswers.com • www.iisadministrator.com

  44. The End Thank You!

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