Docker Swarm is a more opinionated but powerful alternative to Kubernetes, offering features like easy setup, dynamic scaling, and service discovery. However, it has caught up with Kubernetes in terms of performance and is recommended as the best choice for many use cases. Docker Links are legacy and should be replaced with Docker Networking, which offers better connectivity options. Docker and Vagrant solve different problems, with Docker being a native Linux technology and Vagrant provisioning Virtual Machines independent of the host machine. It's possible to run Java applications in containers without breaking Oracle's licensing terms by using OpenJDK-based images or creating your own custom Dockerfile. To communicate between multiple containers across hosts, use Docker Networks instead of legacy Docker Links.