Minecraft On Your Domain

This guide walks you through hosting a Minecraft (Java Edition) server that players reach via a domain like misty-castle.play.cosy-hosting.net — no port numbers, and multiple servers can share the standard Minecraft port.

What You'll Build

Player types misty-castle.play.cosy-hosting.net in Minecraft
        │
        ▼  DNS (A record from the Cosy Domain Provider)
Your host, port 25565
        │
        ▼
MC-Router proxy (runs as a COSY game server)
        │  routes by the hostname the player typed
        ├── misty-castle.play.cosy-hosting.net → Paper server container
        └── swift-harbor.play.cosy-hosting.net → Vanilla server container

The MC-Router (Proxy) template runs itzg/mc-router as a regular COSY game server. It is the only server that publishes port 25565 on the host. The Minecraft servers themselves use the (MC-Router) template variants, which publish no host port at all — instead they carry a mc-router.host Docker label (set via the template annotations field), and the proxy automatically discovers them and forwards each connection to the server whose hostname matches what the player typed.

When do you need this? For a single server you could simply point a domain at your host and publish port 25565 directly. MC-Router pays off when you want several servers on one machine without making players remember port numbers — or when you want to add and remove servers without touching DNS beyond one A record per hostname.

Prerequisites

• A running COSY instance — see Installation
• An Admin or Owner account: the proxy template mounts the Docker socket via a host mount, which only administrators may do
• Your host's public IP address
• Minecraft Java Edition (MC-Router routes Java Edition connections)

Step 1: Claim a Subdomain

If you already own a domain, create an A record pointing at your host and skip to Step 2. Otherwise, the Cosy Domain Provider gives you a free *.play.cosy-hosting.net subdomain:

1. Register an account and verify your email address.
2. Claim a subdomain — on the free plan the label is randomly generated as a two-word name like misty-castle, giving you the address misty-castle.play.cosy-hosting.net. Plus accounts can choose a custom label instead (3–63 characters, lowercase letters, digits, and hyphens; a few labels like www or mail are reserved).
3. Set the Target IP to your host's public IP address (IPv6 optional).

The subdomain starts in PENDING status while the DNS record is created and switches to ACTIVE once it is live. Records use a 5-minute TTL, so changes propagate quickly. You can verify resolution with dig +short misty-castle.play.cosy-hosting.net.

Free accounts can claim one subdomain with a random name; Plus accounts can claim up to five and pick custom labels. Each Minecraft server behind MC-Router needs its own hostname, so plan accordingly (see Adding More Servers).

Step 2: Create the MC-Router Proxy

In COSY, create the proxy as a normal game server:

1. Start the server creation wizard from the server yard.
2. Select Minecraft in the game sidebar and filter by the proxy tag.
3. Choose the MC-Router (Proxy) template — it has no variables to fill in.
4. Create and start the server.

What this template sets up:

• Publishes host port 25565/tcp — the single entrypoint all players connect to
• Mounts the Docker socket read-only so it can watch for containers carrying the mc-router.host label (this is why creating it requires an administrator)
• Sets IN_DOCKER=true, enabling automatic backend discovery — no proxy configuration needed, ever

Make sure port 25565/tcp is open in your host's firewall.

Step 3: Create the Minecraft Server

Now create the actual game server:

1. Start the creation wizard again and select Minecraft.
2. Filter by the mc-router tag and pick a (MC-Router) variant — Paper, Fabric, Forge, NeoForge, Purpur, Vanilla, and modpack variants are available.
3. Fill in the template variables: game version, memory — and most importantly the Router Hostname, which must be exactly the address players will type, e.g. misty-castle.play.cosy-hosting.net.
4. Create and start the server. The first start pulls the image and generates the world, which can take a few minutes.

Unlike the regular Minecraft templates, the (MC-Router) variants publish no host port. The Router Hostname is written into the mc-router.host annotation on the container, and the proxy picks it up automatically as soon as the container is running.

Step 4: Connect

In Minecraft Java Edition: Multiplayer → Add Server, and enter your subdomain as the server address — no port needed:

misty-castle.play.cosy-hosting.net

The connection reaches MC-Router on port 25565, which reads the hostname from the Minecraft handshake and forwards you to the matching server.

Adding More Servers

Every additional server follows the same pattern:

1. Get another hostname pointing at the same IP — a second Domain Provider subdomain (Plus plan), or any DNS provider if you own a domain (a wildcard record like *.mc.example.com lets you add servers without touching DNS at all).
2. Create another (MC-Router) server with that hostname as its Router Hostname.

That's it — no proxy configuration, no new ports, no firewall changes. All servers share port 25565.

Troubleshooting

How It Works Under the Hood

The pieces used here are all standard COSY features:

• The proxy's Docker socket access is a read-only host mount — which is why it's admin-only.
• The Router Hostname is a template variable substituted into a container annotation (mc-router.host) — annotations become Docker labels at launch, and itzg/mc-router watches the Docker API for exactly this label.
• Because the game servers publish no host ports, there are no port collisions no matter how many servers you run.