Tomcat Web Application Deployment
Table of Contents
Deployment is the term used for the process of installing a web application (either a 3rd party WAR or your own custom web application) into the Tomcat server.
Web application deployment may be accomplished in a number of ways within the Tomcat server.
- Statically; the web application is setup before Tomcat is started
- Dynamically; by directly manipulating already deployed web applications (relying on auto-deployment feature) or remotely by using the Tomcat Manager web application
The Tomcat Manager is a web application that can be used interactively (via HTML GUI) or programmatically (via URL-based API) to deploy and manage web applications.
There are a number of ways to perform deployment that rely on the Manager web application. Apache Tomcat provides tasks for Apache Ant build tool. Apache Tomcat Maven Plugin project provides integration with Apache Maven. There is also a tool called the Client Deployer, which can be used from a command line and provides additional functionality such as compiling and validating web applications as well as packaging web application into web application resource (WAR) files.
There is no installation required for static deployment of web applications as this is provided out of the box by Tomcat. Nor is any installation required for deployment functions with the Tomcat Manager, although some configuration is required as detailed in the Tomcat Manager manual. An installation is however required if you wish to use the Tomcat Client Deployer (TCD).
The TCD is not packaged with the Tomcat core distribution, and must therefore be downloaded separately from the Downloads area. The download is usually labelled apache-tomcat-9.0.x-deployer.
TCD has prerequisites of Apache Ant 1.6.2+ and a Java installation. Your environment should define an ANT_HOME environment value pointing to the root of your Ant installation, and a JAVA_HOME value pointing to your Java installation. Additionally, you should ensure Ant's ant command, and the Java javac compiler command run from the command shell that your operating system provides.
- Download the TCD distribution
- The TCD package need not be extracted into any existing Tomcat installation, it can be extracted to any location.
- Read Using the Tomcat Client Deployer
A word on Contexts
In talking about deployment of web applications, the concept of a Context is required to be understood. A Context is what Tomcat calls a web application.
In order to configure a Context within Tomcat a Context Descriptor is required. A Context Descriptor is simply an XML file that contains Tomcat related configuration for a Context, e.g naming resources or session manager configuration. In earlier versions of Tomcat the content of a Context Descriptor configuration was often stored within Tomcat's primary configuration file server.xml but this is now discouraged (although it currently still works).
Context Descriptors not only help Tomcat to know how to configure Contexts but other tools such as the Tomcat Manager and TCD often use these Context Descriptors to perform their roles properly.
The locations for Context Descriptors are:
Files in (1) are named [webappname].xml but files in (2) are named context.xml. If a Context Descriptor is not provided for a Context, Tomcat configures the Context using default values.
Deployment on Tomcat startup
If you are not interested in using the Tomcat Manager, or TCD,
then you'll need to deploy your web applications
statically to Tomcat, followed by a Tomcat startup. The location you
deploy web applications to for this type of deployment is called the
appBase which is specified per Host. You either copy a
so-called exploded web application, i.e non-compressed, to this
location, or a compressed web application resource .WAR file.
The web applications present in the location specified by the Host's
(default Host is "localhost")
appBase attribute (default
appBase is "$CATALINA_BASE/webapps") will be deployed on Tomcat startup
only if the Host's
deployOnStartup attribute is "true".
The following deployment sequence will occur on Tomcat startup in that case:
- Any Context Descriptors will be deployed first.
- Exploded web applications not referenced by any Context Descriptor will then be deployed. If they have an associated .WAR file in the appBase and it is newer than the exploded web application, the exploded directory will be removed and the webapp will be redeployed from the .WAR
- .WAR files will be deployed
Deploying on a running Tomcat server
It is possible to deploy web applications to a running Tomcat server.
If the Host
autoDeploy attribute is "true", the Host will
attempt to de