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Extending the J2EE Deployment API for Disruption-Free Service

WebLogic Server goes above and beyond the specification

Deployment Validation
This feature covers validating the deployment unit and runtime resources needed to deploy. The WebLogic Server Administration Console and WebLogic Workshop tools provide interactive phases of configuration, custom configuration, and pre-deployment validation. While deploying applications with these tools the user will be prompted for an option to configure/deploy and external resources that the application depends on.

For example, if an application depends on a JDBC Data Source the containers will check to see if that Data Source (and its corresponding connection pool) exists. If it doesn't exist, the user will be given the option to configure/deploy that resource. This includes the enhancements that are required in the Deployment API to incorporate the error details needed by the tools to create the missing resources or select suitable alternatives.

Production Redeployment The J2EE Deployment API outlines a basic redeployment strategy where older versions of the application will be replaced by the newer version. There's no mention about the state of HTTP sessions left in the container. In WebLogic Server 9.0 (Diablo) two redeployment strategies are provided.

PRODUCTION/SIDE-BY-SIDE REDEPLOYMENT
WebLogic Server 9.0 introduces a controlled process for deploying new versions of Web applications without disrupting service. A new version of an application can be deployed alongside an existing version and WebLogic will gradually migrate all of the traffic to the new one. So when redeploying an existing application, the old version can be retired gracefully after all of the existing sessions end. If required, a time-out can also be set to retire the old version.

IN-PLACE REDEPLOYMENT
The new version immediately replaces the old version. This strategy is similar to what the J2EE Deployment API outlines.

WebLogic Server 9.0 can also roll back deployments.

WebLogic Server will automatically use the production redeployment strategy when the redeployed application version specifies a different version identifier from the currently deployed application version. A developer can assign a version identifier to an application by specifying it in the application's manifest file. The version identifier can also be assigned to an application during deployment or redeployment using the appversion option in the weblogic.Deployer tool.

Production redeployment can be done either through the administration console or through command-line tools such as weblogic.Deployer and WLST. When using the administration console in Diablo you start making changes by acquiring a lock over the config.xml configuration repository. The changes are left in a pending state and don't take effect until you activate them. This provides a predictable and secure way for distributing configuration changes in a domain. One has to click on the "Lock and Edit" button on the change center on the console to start deploying applications and finish by clicking the "Activate Changes" button on the change center.

When using the administration console the version identifier has to be configured on the application's manifest file. But the weblogic.Deployer tool can configure on the manifest file or specify using the -appversion option.

The weblogic.Deployer tool can also be used to redeploy a new version of an existing application. The old version can be retired by specifying the -retiretimeout option.

Understanding the Implications of Production Redeployment
By default, WebLogic Server destroys current user sessions when you redeploy a Web app. If you want to preserve the user sessions during redeployment, set "save-sessions-enabled" to "true" in the container-descriptor stanza of the weblogic.xml deployment descriptor file. Note, however, that the application still remains unavailable during the time the in-place redeployment takes place.

Testing Applications in Admin Mode
New application versions should to be tested before opening them to external clients. WebLogic Server puts an application in a special Administration Mode when you distribute a new version. External clients can't access applications that are in Admin Mode; an application is only available through an Administration Channel. An Administration Channel can be created in a domain by enabling the domain's Administration Port property. The default Administration Port is 9002. The Administration Channel is a secure channel that will accept only SSL connections. Once it is enabled in a domain all the administration traffic must go through that port.

For example, if a Web application (timeoff.war) with the context root "/timeoff" is deployed to a server in a domain with Administration Port 9002, then the application can be accessed by the URL https://serverhostname:9002/timeoff/.

If the testing yields successful results, the Web application can be started. Then external clients can access it through the regular listen ports configured for the targeted server(s). An application can also be started through tools like weblogic.Deployer or WLST.

Used along with side-by-side deployment or production redeployment, this feature can isolate the new application version. While the old version is still available to external clients without disruption, the new version can be sanity checked.

Module-Level Deployment and Redeployment for Enterprise Applications
WebLogic Server lets you target individual modules of an enterprise application at different server targets or deploy only a subset of available modules of the enterprise application. This provides flexible packaging options so you can bundle a group of related modules together in an enterprise application, but deploy only selected ones on individual servers or clusters in a domain.

This module-level targeting provides fine-grained control in deploying the modules. Module-level targeting can be done using any standard WebLogic deployment tool such as administration console, WLST, or weblogic.Deployer. This can simplify application packaging and distribution by packaging multiple modules in a single distributable EAR, but target only the modules you need to the right servers in a domain.

Module-level deployment using weblogic.Deployer:


java weblogic.Deployer -adminurl http://localhost:7001
-user weblogic -password weblogic
-name mywebapp -targets [email protected]
-stage -deploy c:\files\myApp.ear
Being able to do a live application upgrade is a major factor in achieving a disruption-free service along with other candidates like disruption-free server upgrade, improved visibility into runtime operations and the application runtime information, and flexible, customizable administration tools. With features in WebLogic Diablo like live server upgrades, diagnostic framework, automatic server migration, clustering, customizable administration console, and powerful scripting tools you can achieve a disruption-free service.

More Stories By Balamurali Kothandaraman

Balamurali Kothandaraman is a delivery technologist for education services at BEA Systems Inc. He has over 7 years of experience in Java and J2EE technologies and is a BEA Certified Server Specialist, Administrator, and Instructor. Bala is a frequent speaker at various conferences, including eWorld and JavaOne.

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