So it is passing DEFAULT_JVM_OPTS, JAVA_OPTS and MYAPP_NODE_OPTS into java application. Which is great way to customize docker image to run on specific environment or with specific features.

Vaadin Flow is the Java framework of Vaadin Platform for building modern websites that look great, perform well and make you and your users happy. For instructions about developing web applications ...

Written in Rust, the PyApp utility wraps up Python programs into self-contained click-to-run executables. It might be the easiest Python packager yet.