Docker

To configure our SMP server to be managed by Docker, we simply need to add a few lines to our config.yaml file.

plugins/impulse/config.yaml

instanceName: MyCoolSMP
servers:
  - name: smp
    type: docker
    lifecycleSettings:
      timeouts:
        inactiveGracePeriod: 300
    docker:
      image: "itzg/minecraft-server:latest"
      portBindings:
        - "25566:25565"
      env:
        ONLINE_MODE: "FALSE"
        TYPE: "FABRIC"
        EULA: "TRUE"
        MODRINTH_PROJECTS: "fabricproxy-lite"
      volumes:
        - "/srv/smp:/data"

Let's break that down a bit!

servers section

This is where we can define a list of servers that we want Impulse to manage. In this case, we are defining a single server named smp.

name provides a unique identifier for the server.

exactly. If it does not you will get unexpected behaviour!

lifecycleSettings is where we can set all the config properties related to how a server runs. For our SMP server we are setting the amount of time the server will wait before shutting down after the last player has left to 5 min.

type specifies which broker is managing this server. In this case, we are using the docker broker.

docker section

This section contains all the configuration specific to the Docker broker. If you are familiar with Docker Compose or Kubernetes many of these options may look familiar. If not, never fear! We will explain them all.

image specifies the Docker image that we want to use for this server. In this case, we are using the itzg/minecraft-server image. This image is a very popular image for running Minecraft servers in Docker containers and is the default. Documentation can be found here. Impulse will work with any image, so feel free to change this as needed.

portBindings allows us to define how we want to map ports from the host to the container. In this case, we are mapping all traffic on the host port 25566 to the container port 25565.

env allows us to define environment variables that will be passed to the container. The itzg/minecraft-server image has many environment variables that can be used to configure your MC server. In this case, we are setting up a Fabric server with the fabricproxy-lite mod. It is also set to offline mode as required by Velocity.

volumes allows us to define which directories on the host we want to mount into the container. In this case, we are mounting the /srv/smp directory on the host to the /data directory in the container. This is where the Minecraft server data will be saved. The source directory can be any directory on the host, but it must be mounted to /data for this image.

Configuring Identity Forwarding

Since Velocity is set up with "modern" forwarding and in online mode, we need a bit of configuration on our server before players will be able to connect. Luckily this is very simple! We just need to add a file to the /srv/smp directory that we mounted into the container.

/srv/smp/config/FabricProxy-Lite.toml

hackOnlineMode = true
hackEarlySend = false
hackMessageChain = true
disconnectMessage = "This server requires you to connect with Velocity."
secret = "<YOUR SECRET FROM forwarding.secret HERE>"

You can find the forwarding.secret file next to your velocity.toml.

Pre-pulling the Docker Image

docker pull itzg/minecraft-server:latest