503 - Service Unavailable - How come Tomcat will not start and it complains that port 8080 is already in use?

Background Information

Tomcat will not start and complains that port 8080 is already in use. When accessing the site via a web browser you get a '503 - Service Unavailable' error.

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Answer

Be sure that the APP_SERVER_PORT input variable on your template is set to 8000 (the default) and not 8080. Tomcat uses port 8080, but the APP_SERVER_PORT is the port that HA PROXY forwards traffic to and should be set to 8000.