Technical Details Apache Tomcat Configuration Execute validation of the deployment process prior to placing the Tomcat instance back in circulation.During a deployment execution, clear the directories that Tomcat uses to store copies of the applications at runtime.For each deployment, remove the target Tomcat instance from circulation during the deployment process.Modify Liferay’s deployment process to force it to deploy an atomic WAR file, rather than an exploded application tree.Disable Apache Tomcat’s hot deployment processor via modifications to the Tomcat configuration files.
The overall approach taken for persistent multi-user Apache Tomcat installations is to disable hot deployment at the application server level and include an application server restart in the application deployment process. The specifics of implementation may vary, depending on the delivery toolchain in place, but the overall process is as follows:
The preprocessing that Liferay does to any plugin is recommended to be executed at deploy time in order to minimize build overhead and avoid potential mismatches between the the target Liferay installation and the custom Liferay plugin. These issues are extremely difficult to detect or triage. Liferay portal bundle directory update#
The JVM will at times run into conflicts with the operating system when attempting to update filesystem content during a deployment this can result in corrupted application deployments, as in-memory content fails to overwrite files which are marked as locked on the filesystem. Tomcat has also been observed to have problems cleaning up the global classloader during deployments, which can lead to class loader errors within the JVM, again causing an outage. This is caused by the way that Tomcat handles web application deployments the only remediation step is to restart the application server instance. Enabling hot deployments on a Tomcat application server instance will cause the amount of memory consumed by the permanent generation to increase over time, eventually resulting in an outage. Ongoing leaks in the JVM’s permanent generation memory space. The basic issues presented by the use of hot deployment on Apache Tomcat include the following: Hot deployment is not recommended to be enabled on any environment except for lightweight testing purposes on local developer systems. As a result, Xtivia highly recommends disabling hot deployment at the application server level. Liferay bundles normally have Apache Tomcat’s hot deployment feature enabled while hot deployment is a convenient process that allows the deployed artifacts to be available immediately, there are a number of problems that arise when Tomcat hot deployment is enabled which will cause the system to become unstable over time. Note that while this document is primarily targeted at the deployment of custom Liferay plugins, many of the concepts do apply to non-Liferay web applications being deployed to the Tomcat application server. This blog post describes the overall process recommended by Xtivia for deploying custom Liferay plugin applications to Liferay.
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