Enterprise Integration Servers

Tier 2 Servers

Web/Proxy Server

Developer     01/03           %         02/03       %       Change

Apache      22,045,420      62.23    22,492,327    62.72     0.49

Microsoft    9,739,590      27.49     9,687,454    27.01    -0.48

Zeus           736,744       2.08       768,951     2.14     0.06

SunONE         471,942       1.33       428,004     1.19    -0.14

SunONE (a.k.a. Netscape)

IIS

Apache

Server Directory Layout and Configuration

Directory Layout

• bin: httpd, startup script and other utilities
• cgi-bin: default cgi program directory
• conf: configuration files
• htdocs: documentation root or home page top directory
• icons: images used in htdocs
• include: header files for making web server, i.e. httpd
• libexec: shared objects which include runtime library and modules
• logs: big brother's holder
• man: manual
• proxy: when compiled with --enable-module=proxy

Configuration (httpd.conf)

ServerRoot "/usr/local/apache"
# Dynamic Shared Object (DSO) Support
LoadModule servletexec_module libexec/mod_servletexec.so
Port 80
User nobody
Group nobody
ServerAdmin root@1sa11.bitmotel.com
ServerName 1sa11.bitmotel.com
DocumentRoot "/usr/local/apache/htdocs"

    Options Indexes FollowSymLinks ExecCGI

< Directory >
    Options FollowSymLinks ExecCGI
    AllowOverride None
< /Directory >

ScriptAlias /cgi-bin/ "/usr/local/apache/cgi-bin/"
AddHandler cgi-script .cgi

Virtual Host
 < VirtualHost www.smallco.com >
    ServerAdmin webmaster@mail.smallco.com
    DocumentRoot /groups/smallco/www
    ServerName www.smallco.com
    ErrorLog /groups/smallco/logs/error_log
    TransferLog /groups/smallco/logs/access_log
 < /VirtualHost >

 Redirect / http://www.apache.org/

Apache Modules

• mod_proxy:
  This module allows Apache to act as a caching-proxy server. The proxy fetches the document and returns it to the client. Like your browser, proxy server keeps a copy of the document fetched to reduce Internet traffic. This also improves response time to the user. Most importantly, companies use proxy servers to keep track of which URLs that you download. Corporations typically sets up a firewall to allow the proxy server connecting to the Internet without exposing inside networks. The most popular proxy-caching freeware is Squid, which keeps caches DNS lookups, meta data and especially hot objects cached in RAM. Browser can be configured with auto-proxy and manual-proxy. In auto-proxy, proxy server uses Java script to designate a proxy server or to assign direct connection. Reverse proxy allows the public to access your company's web servers that are not directly accessible from the Internet. (documentation of internal web servers will be fetched and saved on the reverse proxy)
• mod_ssl: openSSL is a free implementation of Netscape's Secure Socket Layer. When a connection starts, certificates are checked and a new session key is agreed between the client and server. (via public key encryption)
• mod_cgi: provides CGI capability (default). suEXEC: provide users the ability to run CGI and SSI programs under "uid" different from the id of the calling web-server. (i.e. nobody) Refer to effective uid/gid in session1.
• mod_jserv: Java engine for supporting servlet. There are commercial Java engines such as Java server, and Jrun which provide server side Java program functionality as CGI.

Application Servers: EJB

Zope is a free, open source application server. Although it is not an EJB technology, it is getting popular in the Linux platform because of its attractive cost and features.

• Database Integration
• Content Management
• Application Development
• Web to Objects

1. Client (e.g. browser) invokes Web server's servlet via http.
2. Servlet calls EJB components (See next graphics for more details)
3. Transact with legacy systems (handled by EJB container or beans)
4. Generate response in html (Select JSP or not)

EJB's main advantage is to provide the service framework for developers of application servers, transaction process monitors, object request brokers, and database management systems.

Architecture of EJB

• Server
• Container (handles transaction and manage database connection pool)
• Component, also called "bean" (not an object)

The EJB server is the core of EJB architecture. It provides transaction, naming (via JNDI), persistence services, and managing EJB containers. (Note: Some vendors do not distinguish server from container.)

The competing products are:

• JBoss - WebMethod will release its new version that integrate with JBoss
• WebLogic
• Enhydra
• iPlanet
• WebSphere
• OAS
• iPortal

Major EJB components are:

• Home Interface
  serves as a factory for EJB objects. Client (e.g. servlet) uses JNDI to retrieve Home Object reference. It then uses home interface to generate (or destroy) EJB objects.
• Remote Interface
  serves the public face of EJBeans. Client goes through remote interface which uses RMI/IIOP (Remote Method Invocation over Internet Inter-Orb Protocol).
• EJB object is the container-generated implementation of the remote interface. It is a network-aware intermediary (proxy) between the client and EJB beans. The client uses EJB object to invoke the business methods of an instance by delegating request to bean.
• The Enterprise Bean Instance: A bean instance is a Java object instance of an enterprise bean class. It contains business logic implementation of the methods defined in the remote interface. Session Beans:
  Represent a task
  One instance per client
  Short-lived as client
  Transient
  Don't survive server crashes

  Note: Session beens are categorized into stateful and stateless. To conserve resource, EJB containers exploit OS's virtual memory concept to swap in (activation) and swap out (passivation) stateful session beans. For stateless session beans, the container could pool only a few beans to serve thousands of clients.

  Entity Beans:
  Represent data (e.g. a row in DBMS table)
  Shared instance for multiple clients
  Long-lived: as the data in DBMS
  Persistent
  Survive server crashes

  Note: A client specifies lookup for either a container-managed or a bean-managed persistence. With container-managed persistence, some database access logic are done by the container. (such as database table, column, and connection pool name are specified in the deployment descriptor file in XML format.) Developers are free from worrying about the the plumbing and concentrate on business logic. For bean-managed persistence, the database connection and SQL are done by the entity EJBeans developed by the EJB programmers.

• The Deployment descriptor
  A deployment descriptor specifies the middleware requirements of a bean. It provides information to the container about how to manage a bean. (such as bean's life-cycle, transaction, persistence and security needs.) Some vendors are using or migrating to XML for the deployment descriptor.

  
  

Java Transaction Service

• TX_BEAN_MANAGED: via begin, commit, and abort statements
• TX_NOT_SUPPORTED: not involve in transaction
• TX_REQUIRED: always run in transaction
• TX_SUPPORTS: if client has a transaction running: yes. Otherwise: no.
• TX_MANDATOR: a transaction must be running when bean is called

Java Message Service

Publish-Subscribe Model

Point-to-Point Model

JMS Clients

• Use JNDI to locate administrative objects.
  ConnectionFactory object
  Destination objects
• Create a JMS connection via ConnectionFactory object
• Established sessions via Connection
• Generate Producers and Consumers with session and Destinations objects.
• Do your own things.

XML

Summary

There are, however, issues concerning enterprise beans compatibilities. Different EJB servers may not communicate with each other since EJB is only a specifications. Not all the vendors will comply with the optional technologies. EJB is still a relatively new technology. (most of the vendors have released their products about 6 months to 1 year old). Overall, the success stories about companies adopting EJB will validate EJB's role in the complicated middleware market.