This is the easiest way to get a game server running in a docker container. Thi guide will help you to build a game server in UE, package it in a docker container, run it on your PC, and run it online
https://dev.epicgames.com/community/learning/tutorials/qBj7/unreal-engine-fab-package-your-game-server-in-a-docker-container-get-it-running-in-your-pc-online