Explanation
https://docs.docker.com/engine/reference/commandline/swarm/

Explanation
Multi-stage builds are a feature of Docker that allows you to use multiple FROM statements in your Dockerfile. Each FROM statement creates a new stage of the build, which can use a different base image and run different commands. You can then copy artifacts from one stage to another, leaving behind everything you don't want in the final image. This optimizes the image size and reduces the attack surface by removing unnecessary dependencies and tools. For example, you can use a stage to compile your code, and then copy only the executable file to the final stage, which can use a minimal base image like scratch. This way, you don't need to include the compiler or the source code in the final image. References:
* Multi-stage builds | Docker Docs
* What Are Multi-Stage Docker Builds? - How-To Geek
* Multi-stage | Docker Docs

Explanation
= The command 'docker service create --name dns-cache -p 53:53/udp dns-cache' creates a swarm service that only listens on port 53 using the UDP protocol. This is because the -p flag specifies the port mapping between the host and the service, and the /udp suffix indicates the protocol to use1. Port 53 is commonly used for DNS services, which use UDP as the default transport protocol2. The dns-cache argument is the name of the image to use for the service.
References:
* docker service create | Docker Documentation
* DNS - Wikipedia
I hope this helps you understand the command and the protocol, and how they work with Docker and swarm.
If you have any other questions related to Docker, please feel free to ask me.

Explanation
= Uninstalling the 'docker-ce' package before installing the 'docker-ee' package will not upgrade Docker Engine CE to Docker Engine EE. It will only remove the existing Docker Engine CE installation and install a new Docker Engine EE installation. This means that any existing containers, images, volumes, networks, and other Docker resources will be lost. To upgrade Docker Engine CE to Docker Engine EE without losing any data, you need to use the migration tool provided by Docker1 or follow the steps described in the Docker documentation2 or other online guides34. References:
* 1: Migrate to Engine 1.10 | Docker Docs
* 2: Install Docker Engine | Docker Docs
* 3: Switching Docker 18.09 Community Edition to Enterprise Engine with no ...
* 4: How to upgrade Docker 18.09 Community Edition to Docker Enterprise 18.09