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This guide will walk you through creating and deploying a multiplayer game with Godot 4.2. If you are using Godot 4.1/4.0/3.x, please be aware that some details may be different.

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Overview

Godot provides great multiplayer capabilities out of the box. We’ll be using Godot’s built-in networking along with Rivet’s Godot plugin to build a server-authoritative multiplayer game on top of Rivet. Godot supports ENet, WebSocket, and WebRTC transports. We’ll be using ENet for this tutorial, but it’s easy to swap out.

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Step 1: Set up the Rivet Godot plugin

Follow the instructions on the Rivet Godot plugin repository to install the plugin. Once the plugin is open, sign in to link your game to Rivet.

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Step 2: Update game code

Add the following code to the relevant places. Add this code to where the game is started: 
func _ready():
	RivetHelper.start_server.connect(start_server)
	RivetHelper.setup_multiplayer()
The setup_multiplayer() call will do a check to properly start a Godot. Add this code wherever the server is started. This function name needs to match the one used in the RivetHelper.start_server.connect call above. 
func start_server():
	peer = ENetMultiplayerPeer.new()
	peer.create_server(DEFAULT_PORT, MAX_PEERS)
	multiplayer.set_multiplayer_peer(peer)
	await Rivet.matchmaker.lobbies.ready({})
This is an example of how a lobby can be found and joined: 
func join_game(new_player_name):
	player_name = new_player_name

	var response = await Rivet.matchmaker.lobbies.find({
		"game_modes": ["default"]
	})

	if response.result == OK:
		RivetHelper.set_player_token(response.body.player.token)

		var port = response.body.ports.default

		peer = ENetMultiplayerPeer.new()
		peer.create_client(port.hostname, port.port)
		multiplayer.set_multiplayer_peer(peer)
	else:
		game_error.emit(response.body)

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Step 3: Deploy to Rivet

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Configure Rivet

Copy the following to rivet.json: 
{
  "engine": {
    "godot": null
  },
  "matchmaker": {
    "max_players": 12,
    "docker": {
      "dockerfile": "Dockerfile",
      "ports": {
        "default": {
          "port": 10567,
          "protocol": "udp"
        }
      }
    },
    "game_modes": {
      "default": {}
    }
  }
}
You can find more information about the Rivet config file in our documentation.

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Write Dockerfile

Write the following Dockerfile 
FROM ghcr.io/rivet-gg/godot-docker/godot:4.2 AS builder
WORKDIR /app
COPY . .
RUN mkdir -p build/linux \
    && godot -v --export-release "Linux/X11" ./build/linux/game.x86_64 --headless

FROM ubuntu:22.04
RUN apt update -y \
    && apt install -y expect-dev \
    && rm -rf /var/lib/apt/lists/* \
    && useradd -ms /bin/bash rivet

COPY --from=builder /app/build/linux/ /app

# Change to user rivet
USER rivet

# Unbuffer output so the logs get flushed
CMD ["sh", "-c", "unbuffer /app/game.x86_64 --verbose --headless -- --server | cat"]

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Deploy game

In the Rivet plugin, we can go to the deploy tab, and select “Staging” from the dropdown. Then, click “Build & Deploy”. This will build the Dockerfile we just created, and upload the Docker image to Rivet’s servers.

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Deploy game client

Now that we’ve deployed the game to Rivet, we can build a game client that will be able to connect to Rivet. First, we need to specify which server we want to connect from the “Playtest” tab. To use the settings that we deployed the server with above, we need to select “Rivet servers”, and set the namespace to “Staging”. Note that changing anything under the “Playtest” tab will require rebuilding or restarting the game, since the tokens are only set when the game is starting. This is also something to verify when shipping builds, you don’t want to upload a version to Steam that tries to connect to your Staging server! To build the client we can either build through Godot’s export system, or simply run the game from the editor. Both are configured to get the tokens needed for the namespace you have set. You don’t need to change anything with how you would export the game normally for this to work!