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WebLogic: The Definitive Guide by Avinash Chugh, Jon Mountjoy

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Application Deployment

WebLogic uses a two-phase deployment strategy. When you initiate a deployment task for an application, it first prepares the application on all target servers and then activates the application in a separate phase. This two-phase approach reduces the likelihood of inconsistent deployment states across a cluster because the application is deployed on target servers only after acknowledging the success of the prepare phase.

During the prepare phase of deployment, copies of the application and its components are distributed to all target servers. In addition, certain validation checks are performed to ensure that the application and its components can be deployed reliably. A deployment enters the activation phase only if the prepare phase completes successfully. The actual deployment occurs during the activation phase — that is, when the application and its components are deployed to each target server. The application is available to clients only after the completion of the activation phase.

By adopting this two-phase deployment strategy, WebLogic can perform intermediate checks that ensure subsequent activation will succeed on all of the target servers. This greatly helps to reduce the risk of an inconsistent and potentially unstable deployment across the domain. In a clustered environment, if deployment fails on any of the target servers during either the prepare or activation phases, the deployment task is rolled back as a whole from all targets. For example, ...

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