Components for Web Applications

1
Components for Web Applications

• Marcia Perry
• Distributed Systems Department
• Ernest Orlando Lawrence Berkeley National
  Laboratory
• August 14, 2001

2
Organization

• Major Components
• Overview of the Build Process
• Configuration
• URL to File System Mappings
• Starting/Stopping Web Server Processes
• More Information

3
Basic Components

• Web server application that responds to HTTP
  requests by returning web resources (e.g., HTML
  files, images, applets, CGI output, ) over the
  Internet
• CGI (Common Gateway Interface)
• conventions used by a web server to execute
  programs
• early technique for creating dynamic content
• scripts/apps executed by web server

4
Advanced Components

• Servlets
• Java classes loaded into and run by a JVM
  (requires a servlet container)
• In response to HTTP requests
• To extend web server functionality
• Adv. over CGI
• Java (one language, portability, convenience,
  type-checking, error-handling, )
• Efficiency (classes usually loaded once not
  necessarily run as separate process)

5
Advanced Components
HelloWWW.java

• import java.servlet. import java.servlet.http.
  import java.io.
• public class HelloWWW extends HttpServlet
• public void doGet(HttpServletRequest req,
  HttpServletResponse resp)
• throws ServletException, IOException
• resp.setContentType(text/html)
• PrintWriter out resp.getWriter()
• out.println(lthtmlgtltbodygtHello
  WWWlt/bodygtlt/htmlgt)
• out.close()

6
Servlet Containers

• Servlet containers can be
• Standalone Integral part of web server (as when
  using a Java-based web server)
• Add-on component to web server Java container
  implementation web server plugin
• Servlet code runs inside Java container
• Java container runs inside of JVM
• Web server plugin opens JVM

7
Advanced Components

• JSPs (Java Server Pages) for mixing static
  content w/ dynamically generated content
• JSPs are automatically translated into servlets
  behind the scenes
• More convenient to write/modify
• Separates content from presentation

8
Advanced Components
Sample JSP page

• ltHTMLgtltHEADgtltTITLEgtWelcome to Our
  Storelt/TITLEgtlt/HEADgt
• ltBODYgtltH1gtWelcome to Our Storelt/H1gtWelcome,
• lt!-- User name is New User for first time
  visitors --gt
• lt Utils.getUserNameFromCookie(request) gt
• To access your account settings, click ltA
  HREFAccount-Settings.htmlgt here.lt/Agt
• Regular HTML for the rest of the on-line stores
  web page.
• lt/BODYgtlt/HTMLgt

9
Advanced Components

• Applets Java code that runs inside browser
• Advantages
• Extends functionality on the client side
• More complicated GUIs than w/ HTML or JavaScript
• Computation can be off-loaded from server
• Users dont have to build, install, and configure
• Disadvantages
• Download time
• Sandbox limits functionality (unless signed)
• Window management by browser

10
Advanced Components

• JavaScript
• Interpretive language w/ object-oriented
  capabilities
• Allows including executable content within web
  pages (e.g., window management, further
  processing)
• Both client and server side

11
Apache

• Apache Industrial strength HTTP/1.1 compliant
  web server
• Highly configurable
• Implements many features in addition to its core
  functionality (e.g., security/access control,
  virtual hosting, CGI script execution, )
• Extensible with third-party modules (e.g.,
  servlet engine, security, WebDAV, )

12
Modules for Apache

• mod-ssl (secure HTTP communication between a
  browser and a web server)
• Provides strong cryptography for privacy
• Provides use of digital signatures for data
  integrity
• Allows server and/or client authentication
• Integrates SSL/TLS protocols w/ Apache (via
  OpenSSL)
• mod-dav (publishing into the web environment)
• Provides server support for WebDAV (web-based
  distributed authoring and versioning)
• Implements WebDAV extensions to HTTP 1.1

13
Tomcat

• Tomcat Java-based web server servlet container
  w/ JSP environment
• Execution modes
• Standalone default mode for Tomcat
• Out-of-process add-on web server plugin opens
  JVM outside web server plugin and JVM
  communicate using IPC mechanism (TCP/IP sockets
  and special protocol)
• Most popular!!

14
Tomcat Execution Modes

• Standalone
• Not as fast as Apache for static pages
• Not as configurable as Apache
• Not as robust as Apache
• May not support functionality found only in
  Apache modules (e.g., Perl, PHP, security)
• Mainly for development and debugging

15
Tomcat and Apache

• Communication mechanism between Tomcat and
  Apache
• Termed web server adapter or connector
• Implemented as library (e.g., mod_jserv.so,
  mod_jk.so)
• Uses/manages TCP connections
• Uses the AJPV12/AJPV13 communication protocol

16
A Basic Installation
servlet
17
How Apache Tomcat Interoperate
http//host/path/to/resource
Apache
adapter
Apache in standalone mode Tomcat in
out-of-process add-on mode
18
Building and Installing Apache and Tomcat

• Apache supports statically-linked and
  dynamically-linked modules (DSOs)
• Script to automate the build/configure process
  www-itg.lbl.gov/Grid/projects/WebServer-SG.html
• Step-by-step procedure www-itg.lbl.gov/mperry/ap
  ache_build.html

19
Overview of the Build Process

• Assumptions
• Java already installed (JDK 1.2/JDK1.3)
• APACHE /usr/local/apache
• TOMCAT /usr/local/tomcat
• Build OpenSSL (needed for mod_ssl)
• Configure mod_ssl
• Build mod_dav.a
• Build and install Apache w/ DSO support

20
Configuration

• Apache
• httpd.conf (in APACHE/conf/) master
  configuration file
• tomcat-apache.conf (generated by tomcat at
  startup from tomcat.conf) included in httpd.conf
  to give mod_jserv info about Tomcat
• Tomcat (in TOMCAT/conf/)
• server.xml global configuration file for Tomcat
• tomcat.conf for interoperability between Apache
  Tomcat
• web.xml deployment descriptor configures Tomcat
  web applications (contexts) by mapping web app
  components and properties

21
Configuring the Ports
Default configuration
http/8080
Apache
Tomcat
22
Configuring the Ports
server.xml lt! disable webserver on port 8080
ltConnector classNameorg.apache.tomcat.servi
ce.SimpleTcpConnectorgt ltParameter
namehandler valueorg.apache.tomcat.service.ht
tp.HttpConnectionHandler/gt ltParameter
nameport value8080/gt
lt/Connectorgt --gt ltConnector
classNameorg.apache.tomcat.service.SimpleTcpConn
ectorgt ltParameter namehandler
valueorg.apache.tomcat.service.connector.Ajp12Co
nnectionHandler/gt ltParameter nameport
value8007/gt lt/Connectorgt
23
Configuring the Ports

• tomcat.conf
• Tell Apache to load the shared object
  communication module
• LoadModule jserv_module libexec/mod_jserv.so
• Set communication protocol and port
• ApJServDefaultProtocol ajpv12
• ApJServDefaultPort 8007

24
Configuring the Ports

• httpd.conf
• ServerRoot /usr/local/apache
• Heres where we can overwrite default ports
• Port 80
• ltIfDefine SSLgt
• Listen 80
• Listen 443
• lt/IfDefinegt
• ltVirtualHost _default_443gt

25
Sample File System

• APACHE

• TOMCAT

26
URL to File System Mappings

• httpd.conf
• DocumentRoot /usr/local/apache/htdocs
• ltIfDefine SSLgt
• General setup for the virtual host
• DocumentRoot /usr/local/apache/securedocs
• Lots of stuff
• lt/IfDefinegt
• Include /usr/local/tomcat/conf/tomcat-apache.conf

http//hostname / foo/
/usr/local/apache/htdocs/ foo/
https//hostname / foo/
/usr/local/apache/securedocs/ foo/
27
Apache Directory Access

• Restrict access on per-directory basis via
  httpd.conf.
• ltDirectory /gt
• AllowOverride None
• lt/Directorygt
• ltDirectory /usr/local/apache/htdocs/webDAVdirgt
• Order deny, allow
• Deny from all
• Allow from .lbl.gov
• DAV On
• lt/Directorygt

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Apache Directory Access

• Per-directory access restriction (httpd.conf)
• ltDirectory /usr/local/apache/htdocs/webDAVdirgt
• Order deny, allow
• ltLimit GET POST gt
• Deny from all
• Allow from .lbl.gov
• lt/Limitgt
• ltLimit PUT DELETE MKCOL COPY MOVE LOCK UNLOCKgt
• Deny from all
• Allow from 131.243.2
• lt/Limitgt
• lt/Directorygt

29
Tomcat File System
index.html
30
URL to File System Mappings

• tomcat-apache.conf
• AddType text/jsp .jsp
• AddHandler jserv-servlet .jsp
• Alias /examples /usr/local/tomcat/webapps/examples
  
• ApJServMount /examples/servlet /examples
• ltLocation /examples/WEB-INF/ gt
• AllowOverride none
• deny from all
• lt/Locationgt

31
URL to File System Mappings

• server.xml
• ltContext path/examples docBasewebapps/examp
  les debug0 reloadabletrue
• lt/Contextgt

SIDE NOTES (1) path is used in URLs docBase
is actual directory name on f/s. They do NOT have
to match! (2)Tomcat docs recommend turning on
servlet auto-reloading only for development.
32
Configuring a Context

• web.xml
• ltweb-appgt
• ltservletgt
• ltservlet-namegtMyServletlt/servlet-namegt
• ltservlet-classgtSimpleServletlt/servlet-classgt
• lt/servletgt
• ltservlet-mappinggt
• ltservlet-namegtMyServletlt/servlet-namegt
• lturl-patterngt/docservlet/lt/url-patterngt
• lt/servlet-mappinggt
• lt/web-appgt

URLs
https//server/context/url-pattern/servlet-name
servlet-class servlet default
url-pattern
http//shaggy/ examples/servlet/MyServlet
examples/servlet/SimpleServlet
examples/docservlet/MyServlet
examples/docservlet/NewServlet
33
Starting Tomcat

• Do NOT start Tomcat as root.
• Create a new user account or use an existing one.
• Use the startup.sh script in TOMCAT/bin
• If necessary add or modify entries for JAVA_HOME,
  TOMCAT_HOME, and CLASSPATH.

34
Tomcat Startup Script

• TOMCAT/bin/startup
• !/bin/sh
• TOMCAT_HOME/usr/local/tomcat
• export TOMCAT_HOME
• PATH/usr/local/java/binPATH
• export PATH
• CLASSPATHCLASSPATH/usr/local/MyJavaPkg.
• export CLASSPATH
• BASEDIRdirname 0
• BASEDIR/tomcat.sh start _at_

35
Executing Apache

• Specify user and group to run as (in httpd.conf)
• User nobody
• Group cpc
• Remember to add libexec/ to LD_LIBRARY_PATH
• Start Apache as root
• cd /usr/local/apache/bin
• ./apachectl startssl

36
Starting Apache

• Sample startup script APACHE/start
• !/bin/sh
• LD_LIBRARY_PATH/usr/local/apache/libexec/usr/loc
  al/openssl-0.9.6LD_LIBRARY_PATH
• export LD_LIBRARY_PATH
• /usr/local/apache/bin/apachectl startssl
• echo Apache started

37
Starting Apache

• Usage APACHE/bin/httpd -d directory -v -h
  -l
• -d specify alternative ServerRoot
• -v show version number
• -h list available command line options
• -l list compiled-in (static) modules

38
Stopping Apache/Tomcat

• Tomcat
• As tomcat user run TOMCAT/bin/shutdown.sh
• Apache
• As root, use apachectl (or write a stop
  script)
• cd /usr/local/apache/bin
• ./apachectl stop
• OR
• cd /usr/local/apache
• ./stop

39
More Information

• Wainright, P., Professional Apache, Wrox Press
  Ltd.
• http//www.webdav.org/
• http//httpd.apache/org/docs/
• http//jakarta.apache.org/tomcat/
• http//java.sun.com/products/servlet/download/

40
More Information

• http//www.ccl.net/cca/software/UNIX/apache/
• http//www-itg.lbl.gov/mperry/apache_build.html
• http//www-itg.lbl.gov/Grid/projects/WebServer-SG.
  html
• https//idcg-ca.lbl.gov
• http//www.modssl.org/