Kuvel

Overview

Kuvel, A service discovery plugin for Velocity. It will automatically discover Minecraft servers and register/unregister them in Velocity.

Features

• Monitor Minecraft pods in a Kubernetes cluster and automatically register/unregister them with Velocity
• Create a LoadBalancer server and distribute players trying to join to the linked servers.
• Synchronize server names across multiple Velocity servers using Redis

Installing

The Plugin can be downloaded from Releases. Download Kuvel.jar and install it into Velocity plugins directory. Also, you have to fill in the configuration file.

# The kubernetes namespace to use for the server discovery.
namespace: ""
# Server name synchronization by Redis is required in load-balanced environments using multiple Velocity.
redis:
  group-name: "production"
  connection:
    hostname: "redis"
    port: 6379
    # username is optional. if you have authentication enabled, you can use it here. Or leave it blank or null.
    username: "default"
    # password is optional. if you have authentication enabled, you can use it here. Or leave it blank or null.
    password: "password"

Alternatively you can use environment variables to configure Kuvel. The environment variable will override the config.yml and are KUVEL_NAMESPACE, KUVEL_REDIS_GROUPNAME, KUVEL_REDIS_CONNECTION_HOSTNAME, KUVEL_REDIS_CONNECTION_PORT, KUVEL_REDIS_CONNECTION_USERNAME, and KUVEL_REDIS_CONNECTION_PASSWORD.

In order for Kuvel to monitor the server, you must request permission from Kubernetes to allow Velocity pods discovery Minecraft servers. For Velocity pods, please allow get/list/watch to Pods and ReplicaSets.

apiVersion: v1
kind: ServiceAccount
metadata:
  name: velocity-account
  namespace: default
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: velocity-clusterrolebiding
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: view
subjects:
- kind: ServiceAccount
  name: velocity-account
  namespace: default

# Apply ServiceAccount to the Velocity pod
apiVersion: apps/v1
kind: ...
# ...
spec:
  serviceAccountName: velocity-account
# ...

Enable Service Discovery on the Minecraft Servers

To tell Kuvel that the pod is a Minecraft server, use Label feature of Kubernetes.

Label Name	Value
kuvel.azisaba.net/enable-server-discovery	true / false
kuvel.azisaba.net/preferred-server-name	Name of the server you wish to register with Velocity
kuvel.azisaba.net/initial-server	true / false

Pod

apiVersion: v1
kind: Pod
metadata:
  name: test-server
  labels:
    kuvel.azisaba.net/enable-server-discovery: "true" # Required for Kuvel to detect Minecraft servers.
    kuvel.azisaba.net/preferred-server-name: : "test-server" # Required for Kuvel to name the server
    # kuvel.azisaba.net/initial-server: "true" # Uncomment out this line if you want to make this server the initial server.   
spec:
  containers:
    - name: test-server
      image: itzg/minecraft-server:java8
      ports:
        - containerPort: 25565

Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: test-server-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: test-server-deployment
  template:
    metadata:
      labels:
        app: test-server-deployment
        kuvel.azisaba.net/enable-server-discovery: "true" # Required for Kuvel to detect Minecraft servers.
        kuvel.azisaba.net/preferred-server-name: "test-server" # Required for Kuvel to name the server
        # kuvel.azisaba.net/initial-server: "true" # Uncomment out this line if you want to make this server the initial server.
    spec:
      containers:
        - name: test-server
          image: itzg/minecraft-server:java8
          ports:
            - containerPort: 25565

In both cases, the server is registered under the name test-server.

However, if there are two or more servers with the same name, a number will be assigned after the server name. Specifically, if there are two pods with the server name test-server, one will be test-server and the other will be test-server-1.

Load Balancer

On parallelizable servers such as Lobby, it is sometimes desirable to distribute the number of players as much as possible. This is where Kuvel's LoadBalancer feature comes in handy.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: lobby-deployment
  labels:
    kuvel.azisaba.net/enable-server-discovery: "true"
    kuvel.azisaba.net/preferred-server-name: "lobby"
    # kuvel.azisaba.net/initial-server: "true" # Uncomment out this line if you want to make this load balancer server the initial server.
spec:
  replicas: 3
  selector:
    matchLabels:
      app: lobby-deployment
  template:
    metadata:
      labels:
        app: lobby-deployment
        kuvel.azisaba.net/enable-server-discovery: "true"
        kuvel.azisaba.net/preferred-server-name: "lobby"
        # kuvel.azisaba.net/initial-server: "true" # Uncomment out this line if you want to make this server the initial server.
    spec:
      containers:
        - name: lobby
          image: itzg/minecraft-server:java8
          ports:
            - containerPort: 25565

By applying a Label to a Deployment, Kuvel's LoadBalancer feature can be activated.

1. Distribute players who try to join the Load Balancer server to the pods under ReplicaSet.
2. Synchronize with Kubernetes ReplicaSet and automatically register/unregister forwarding destinations

Using this, you can implement a mechanism to randomly connect to lobby-1, lobby-2, or lobby-3 when /server lobby is invoked.

Synchronize Server Names in Multi Velocity Environment

In a Kubernetes cluster, pods can be created at almost the same time, and this can cause a fatal problem in a parallel Velocity environment because it is possible that different Velocity servers have different registration names. Kuvel provides name synchronization using Redis to avoid this issue. Kuvel uses keys whose key name begins with kuvel:.

On 1.x, this feature was optional, but since 2.0.0, this setting became enabled by default.

License

GNU General Public License v3.0