Tomcat cluster farm deployer attribute “watchDir”

Question

I was looking at the documentation of Tomcat 7, to understand how the clusters work.
The documentation talks about a Deployer tag:

<Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
                    tempDir="/tmp/war-temp/"
                    deployDir="/tmp/war-deploy/"
                    watchDir="/tmp/war-listen/"
                    watchEnabled="false"/>

But the documentation about it is very poor: http://tomcat.apache.org/tomcat-7.0-doc/config/cluster-deployer.html

I found something in the javadocs of the class http://tomcat.apache.org/tomcat-6.0-doc/api/org/apache/catalina/ha/deploy/FarmWarDeployer.html

What I can't find is what is the attribute watchEnabled?

Answer 1

Here some knowledge about it : - Deployer must be declared inside a section

• watchDir is the directory where you can put your delivery. The deployment process will start from here

• deployDir is the directory where your application will be deployed (most probably webapps/ )

• and tempDir is the directory used by the server while the deployment is underway.

• FarmWarDeployer is the only deployer implementation that I know. If you wish to extend this one, you can probably set your own implementation

• WatchEnabled should be set to true on your master node and false on other nodes. The application will be deployed from the master to the other nodes.

Best regards, Cyril

Answer 2

One of the Tomcat instances must be declared with watchEnabled=true. It monitors the state of the watchdir and propagates changes in it (new WARs or deletions) to the other members of the cluster, at least those that are running the FarmWarDeployer.

You are entirely correct about the lamentable state of the documentation. I had to look at the source code.

Answer 3

If you set watchEnabled=true, an instance of WarWatcher will start.

WarWatcher monitors the folder for war files and checks if new files have surfaced, or existing ones have been updated, etc. You can also adjust watcher checks frequency through FarmWarDeployer's processDeployFrequency flag.