Tomcat starts slowly in docker container

Just a little reminder to self: when running Tomcat with Java 8 in an Ubuntu Docker container, Tomcat will take a very long time (minutes!) to start with even the simplest web application.

The issue is actually documented (not entirely Docker-related). The solution is to modify JAVA_OPTS to use a different random device:

JAVA_OPTS=-Djava.security.egd=file:/dev/urandom