6. Application Deployment

Application Deployment

The term application deployment refers to the process of making an application, library, or module available for processing client requests in a WebLogic Server domain. This process is actually unpacking the application package components, putting them into directories, and preparing them to work via WebLogic Server and resources.

Deployment components and terminology

Before we dive deeper into the deployment process let's introduce the following terms:

Applications: The definition of an application is not that simple. An application for an end user can be a whole chain of components from user interface to database, although the user is not aware of all these components. So an application consists of a program or group of programs designed for end users. Application software can be divided into two general classes: systems software and applications software. Systems software consists of low-level programs that interact with the computer at a very basic level.

Application module: It is an XML document that configures JEE resources such as JDBC, JMS, and EJBs. Application modules can be deployed as standalone modules in which their resources are bound to the global JNDI tree

Application install directory: It is a WebLogic Server directory structure, designed to help organize deployment files, and generate deployment configuration artifacts for an application or module. Also referred to as an application root directory.

Application version: A string value that identifies the version of a deployed application. It is located in the manifest file.

Deployment configuration: The process of defining the deployment descriptor values required to deploy an application to a particular WebLogic Server domain.

Deployment descriptor: It is an XML document used to define the J2EE behavior or WebLogic Server configuration of an application or module at deployment time.

Deployment plan: It is an XML document that defines an application's WebLogic Server deployment configuration for a specific WebLogic Server environment. A deployment plan resides outside the application's archive file, and can apply changes to deployment properties stored in the application's existing WebLogic Server deployment descriptors.

Distribution: It is the process by which WebLogic Server copies deployment source files to target servers for deployment Production redeployment: It is the WebLogic Server redeployment strategy that deploys a new version of a production application alongside an older version, while automatically managing HTTP connections to ensure uninterrupted client access.

Staging mode: It is the method WebLogic server uses to make deployment files available to target servers in a domain. Staging modes determine whether files are distributed to target WebLogic Managed Servers before deployment, or not.

The deployment standard: JSR-88 The following diagram shows the components of a JSR-88-compliant deployment API (Application Programming Interface).

All these following XMLs are standard JEE descriptor files:

• application.xml: This is the global application configuration file, which contains the common settings for all application modules contained in the EAR (Enterprise Archive). 
• ejb-jar.xml: This is the deployment descriptor when deploying an EJB application.
• web.xml: This represents the core of a generic Java web application. It provides configuration and deployment information for the Web components that comprise a Web application contained in a WAR (Web Application Archive).
• WebLogic.xml: This is the WebLogic-specific deployment descriptor file. The WebLogic.xml deployment descriptor follows a WebLogic-specific schema that is used only by Oracle WebLogic Server. It allows you to enable and configure Web application features that are not part of the JEE specification, such as changing the default root URL path of the Web application or directing application log messages to a dedicated log file. 
•  WebLogic-application.xml: This is the WebLogic server-specific deployment descriptor extension for the application.xml. Like all the other WebLogic-application.xml WebLogic-application.xml WebLogic-specific descriptor files, this file also enables the use of specific WebLogic features that are not a part of the JEE standards. 
• WebLogic-ejb-jar.xml: This is the WebLogic-specific descriptor for deploying an EJB application the WebLogic-ejb-jar.xml deployment descriptor follows a schema that is used only by Oracle WebLogic Server. It allows you to enable and configure EJB features that are not part of the JEE specification, such as clustering, load balancing, and failover for remote EJBs, tuning EJB performance using pool and cache settings, and many more.
• plan.xml: This is an optional XML file associated with an application; it resides outside an application archive and sets or overrides the values in the JEE deployment descriptors. It allows a single application to be easily customized to multiple deployment environments.