mc-router/README.md

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Routes Minecraft client connections to backend servers based upon the requested server address.

# Usage

```text
  -api-binding host:port
    	The host:port bound for servicing API requests (env API_BINDING)
  -auto-scale-up
      Increase Kubernetes StatefulSet Replicas (only) from 0 to 1 on respective backend servers when accessed (env AUTO_SCALE_UP)
  -connection-rate-limit int
    	Max number of connections to allow per second (env CONNECTION_RATE_LIMIT) (default 1)
  -cpu-profile string
    	Enables CPU profiling and writes to given path (env CPU_PROFILE)
  -debug
    	Enable debug logs (env DEBUG)
  -in-kube-cluster
    	Use in-cluster Kubernetes config (env IN_KUBE_CLUSTER)
  -kube-config string
    	The path to a Kubernetes configuration file (env KUBE_CONFIG)
  -in-docker-swarm
      Use in-swarm Docker config (env IN_DOCKER_SWARM)
  -docker-timeout
      Timeout configuration in seconds for the Docker Swarm integration (env DOCKER_TIMEOUT) (default 0)
  -docker-refresh-interval
      Refresh interval in seconds for the Docker Swarm integration (env DOCKER_REFRESH_INTERVAL) (default 15)
  -mapping string
    	Comma-separated mappings of externalHostname=host:port (env MAPPING)
  -metrics-backend string
    	Backend to use for metrics exposure/publishing: discard,expvar,influxdb (env METRICS_BACKEND) (default "discard")
  -metrics-backend-config-influxdb-addr string
    	 (env METRICS_BACKEND_CONFIG_INFLUXDB_ADDR)
  -metrics-backend-config-influxdb-database string
    	 (env METRICS_BACKEND_CONFIG_INFLUXDB_DATABASE)
  -metrics-backend-config-influxdb-interval duration
    	 (env METRICS_BACKEND_CONFIG_INFLUXDB_INTERVAL) (default 1m0s)
  -metrics-backend-config-influxdb-password string
    	 (env METRICS_BACKEND_CONFIG_INFLUXDB_PASSWORD)
  -metrics-backend-config-influxdb-retention-policy string
    	 (env METRICS_BACKEND_CONFIG_INFLUXDB_RETENTION_POLICY)
  -metrics-backend-config-influxdb-tags value
    	any extra tags to be included with all reported metrics (env METRICS_BACKEND_CONFIG_INFLUXDB_TAGS)
  -metrics-backend-config-influxdb-username string
    	 (env METRICS_BACKEND_CONFIG_INFLUXDB_USERNAME)
  -port port
    	The port bound to listen for Minecraft client connections (env PORT) (default 25565)
  -routes-config string
        The path to the routes config file (env ROUTES_CONFIG)
  -version
    	Output version and exit (env VERSION)
```

# REST API

* `GET /routes` (with `Accept: application/json`)

   Retrieves the currently configured routes

* `POST /routes` (with `Content-Type: application/json`)

  Registers a route given a JSON body structured like:
  ```json
  {
    "serverAddress": "CLIENT REQUESTED SERVER ADDRESS",
    "backend": "HOST:PORT"
  }
  ```

* `POST /defaultRoute` (with `Content-Type: application/json`)

  Registers a default route to the given backend. JSON body is structured as:
  ```json
  {
    "backend": "HOST:PORT"
  }
  ```

* `DELETE /routes/{serverAddress}`

  Deletes an existing route for the given `serverAddress`

# Docker Multi-Architecture Image

The [multi-architecture image published at Docker Hub](https://hub.docker.com/repository/docker/itzg/mc-router) supports amd64, arm64, and arm32v6 (i.e. RaspberryPi).

# Docker Compose Usage

The following diagram shows how [the example docker-compose.yml](docs/docker-compose.yml)
configures two Minecraft server services named `vanilla` and `forge`, which also become the internal
network aliases. _Notice those services don't need their ports exposed since the internal
networking allows for the inter-container access._

The `router` service is only one of the services that needs to exposed on the external
network. The `--mapping` declares how the hostname users will enter into their Minecraft client
will map to the internal services.

![](docs/compose-diagram.png)

To test out this example, I added these two entries to my "hosts" file:

```
127.0.0.1 vanilla.example.com
127.0.0.1 forge.example.com
```

# Routing Configuration

The routing configuration allows routing via a config file rather than a command. 
You need to set `-routes-config` or `ROUTES_CONFIG` env variable.
The following shows a JSON file for routes config, where `default-server` can also be `null` or omitted:

```json
{
  "default-server": "vanilla:25565",
  "mappings": {
    "vanilla.example.com": "vanilla:25565",
    "forge.example.com": "forge:25565"
  }
}
```

# Kubernetes Usage

## Using Kubernetes Service auto-discovery

When running `mc-router` as a Kubernetes Pod and you pass the `--in-kube-cluster` command-line argument, then it will automatically watch for any services annotated with
- `mc-router.itzg.me/externalServerName` : The value of the annotation will be registered as the external hostname Minecraft clients would used to connect to the routed service. The service's clusterIP and target port are used as the routed backend. You can use more hostnames by splitting them with comma.
- `mc-router.itzg.me/defaultServer` : The service's clusterIP and target port are used as the default if no other `externalServiceName` annotations applies.

For example, start `mc-router`'s container spec with

```yaml
image: itzg/mc-router
name: mc-router
args: ["--in-kube-cluster"]
```

and configure the backend minecraft server's service with the annotation:

```yaml
apiVersion: v1
kind: Service
metadata:
  name: mc-forge
  annotations:
    "mc-router.itzg.me/externalServerName": "external.host.name"
```

you can use multiple host names:

```yaml
apiVersion: v1
kind: Service
metadata:
  name: mc-forge
  annotations:
    "mc-router.itzg.me/externalServerName": "external.host.name,other.host.name"
```

mc-router will pick the service port named either `minecraft` or `mc-router`. If neither port names exist, it will use port value 25565.

## Example Kubernetes deployment

[This example deployment](docs/k8s-example-auto.yaml)
* Declares an `mc-router` service that exposes a node port 25565
* Declares a service account with access to watch and list services
* Declares `--in-kube-cluster` in the `mc-router` container arguments
* Two "backend" Minecraft servers are declared each with an
  `"mc-router.itzg.me/externalServerName"` annotation that declares their external server name(s)

```bash
kubectl apply -f https://raw.githubusercontent.com/itzg/mc-router/master/docs/k8s-example-auto.yaml
```

![](docs/example-deployment-auto.drawio.png)

#### Notes
* This deployment assumes two persistent volume claims: `mc-stable` and `mc-snapshot`
* I extended the allowed node port range by adding `--service-node-port-range=25000-32767`
  to `/etc/kubernetes/manifests/kube-apiserver.yaml`

#### Auto Scale Up

The `-auto-scale-up` flag argument makes the router "wake up" any stopped backend servers, by changing `replicas: 0` to `replicas: 1`.

This requires using `kind: StatefulSet` instead of `kind: Service` for the Minecraft backend servers.

It also requires the `ClusterRole` to permit `get` + `update` for `statefulsets` & `statefulsets/scale`,
e.g. like this (or some equivalent more fine-grained one to only watch/list services+statefulsets, and only get+update scale):

```yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: services-watcher
rules:
- apiGroups: [""]
  resources: ["services"]
  verbs: ["watch","list"]
- apiGroups: ["apps"]
  resources: ["statefulsets", "statefulsets/scale"]
  verbs: ["watch","list","get","update"]
```

# Docker Swarm Usage

## Using Docker Swarm Service auto-discovery

When running `mc-router` in a Docker Swarm environment you can pass the `--in-docker-swarm` 
command-line argument and it will poll the Docker API periodically to find all the running
services for minecraft instances. To enable discovery you have to set the `mc-router.host`
label on the service. These are the labels scanned:

- `mc-router.host`: Used to configure the hostname the Minecraft clients would use to 
  connect to the server. The service endpoint will be used as the routed backend. You can 
  use more than one hostname by splitting it with a comma.
- `mc-router.port`: This value must be set to the port the Minecraft server is listening on.
  The default value is 25565.
- `mc-router.default`: Set this to a truthy value to make this server the deafult backend.
  Please note that `mc-router.host` is still required to be set.
- `mc-router.network`: Specify the network you are using for the router if multiple are 
  present in the service. You can either use the network ID, it's full name or an alias.

## Example Docker Swarm deployment

Refer to [this example docker-compose.yml](docs/swarm.docker-compose.yml) to see how to
configure two different Minecraft servers and a `mc-router` instance. Notice how you don't 
have to expose the Minecraft instances ports, but all the containers are required to be in
the same network.

# Development

## Building locally with Docker

```bash
docker build -t mc-router .
```

## Build locally without Docker

After [installing Go](https://go.dev/doc/install) and doing a `go mod download` to install all required prerequisites, just like the [Dockerfile](Dockerfile) does, you can:

```bash
make test # go test -v ./...
go build ./cmd/mc-router/
```

## Skaffold

For "in-cluster development" it's convenient to use https://skaffold.dev. Any changes to Go source code
will trigger a go build, new container image pushed to registry with a new tag, and refresh in Kubernetes
with the image tag used in the deployment transparently updated to the new tag and thus new pod created pulling new images,
as configured by [skaffold.yaml](skaffold.yaml):

    skaffold dev

When using Google Cloud (GCP), first create a _Docker Artifact Registry_,
then add the _Artifact Registry Reader_ Role to the _Compute Engine default service account_ of your _GKE `clusterService` Account_ (to avoid error like "container mc-router is waiting to start: ...-docker.pkg.dev/... can't be pulled"),
then use e.g. `gcloud auth configure-docker europe-docker.pkg.dev` or equivalent one time (to create a `~/.docker/config.json`),
and then use e.g. `--default-repo=europe-docker.pkg.dev/YOUR-PROJECT/YOUR-ARTIFACT-REGISTRY` option for `skaffold dev`.

## Performing snapshot release with Docker

```bash
docker run -it --rm \
  -v ${PWD}:/build -w /build \
  -v /var/run/docker.sock:/var/run/docker.sock \
  goreleaser/goreleaser \
  release --snapshot --rm-dist
```

# Related Projects

* https://github.com/haveachin/infrared