Proof of concept to use HAProxy to route traffic to relevant Minecraft server (not thoroughly tested)

README.md

Proof of concept to use HAProxy to route traffic to relevant Minecraft server (not thoroughly tested)

• Currently using static IP addresses in Map file, if using DNS name they need to be resolved

backends.map

one.minecraft.local 172.19.0.3
three.minecraft.local 172.19.0.4

compose.yaml

services:
  haproxy:
    image: haproxy:3.4
    
    configs:
      - source: haproxy_config
        target: /usr/local/etc/haproxy/haproxy.cfg
    volumes:
      - ./minecraft.lua:/etc/haproxy/minecraft.lua
      - ./backends.map:/data/backends.map
    ports:
      - "25565:25565"

  minecraft_one:
    build:
      dockerfile: minecraft.Dockerfile
    
    configs:
      - source: minecraft_one_config
        target: /app/server.properties

  minecraft_two:
    build:
      dockerfile: minecraft.Dockerfile
    
    configs:
      - source: minecraft_two_config
        target: /app/server.properties

  minecraft_three:
    build:
      dockerfile: minecraft.Dockerfile
    
    configs:
      - source: minecraft_three_config
        target: /app/server.properties

configs:
  haproxy_config:
    content: |
      global
          lua-load /etc/haproxy/minecraft.lua

      frontend minecraft_proxy
          bind :25565
          mode tcp
          log global
          
          tcp-request inspect-delay 3s
          
          tcp-request content lua.parse_mc_handshake if { req_len gt 5 }

          tcp-request content set-var(txn.target_ip) var(txn.mc_server_name),lower,map(/data/backends.map)

          use_backend dynamic_minecraft if { var(txn.target_ip) -m found }

      backend dynamic_minecraft
          mode tcp

          tcp-request content set-dst var(txn.target_ip)
          tcp-request content set-dst-port int(25565)

          server dynamic_srv 0.0.0.0:0
  minecraft_one_config:
    content: |
      accepts-transfers=false
      allow-flight=false
      broadcast-console-to-ops=true
      broadcast-rcon-to-ops=true
      bug-report-link=
      chat-spam-threshold-seconds=10
      command-spam-threshold-seconds=10
      difficulty=easy
      enable-code-of-conduct=false
      enable-jmx-monitoring=false
      enable-query=false
      enable-rcon=false
      enable-status=true
      enforce-secure-profile=true
      enforce-whitelist=false
      entity-broadcast-range-percentage=100
      force-gamemode=false
      function-permission-level=2
      gamemode=survival
      generate-structures=true
      generator-settings={}
      hardcore=false
      hide-online-players=false
      initial-disabled-packs=
      initial-enabled-packs=vanilla
      level-name=world
      level-seed=
      level-type=minecraft\:normal
      log-ips=true
      management-server-allowed-origins=
      management-server-enabled=false
      management-server-host=localhost
      management-server-port=0
      management-server-secret=d9MEMEdjywnNDKvzmNkbrJGaiSSzJ93rimCyq2gK
      management-server-tls-enabled=true
      management-server-tls-keystore=
      management-server-tls-keystore-password=
      max-chained-neighbor-updates=1000000
      max-players=20
      max-tick-time=60000
      max-world-size=29999984
      motd=Minecraft Server One
      network-compression-threshold=256
      online-mode=true
      op-permission-level=4
      pause-when-empty-seconds=60
      player-idle-timeout=0
      prevent-proxy-connections=false
      query.port=25565
      rate-limit=0
      rcon.password=
      rcon.port=25575
      region-file-compression=deflate
      require-resource-pack=false
      resource-pack=
      resource-pack-id=
      resource-pack-prompt=
      resource-pack-sha1=
      server-ip=
      server-port=25565
      simulation-distance=10
      spawn-protection=16
      status-heartbeat-interval=0
      sync-chunk-writes=true
      text-filtering-config=
      text-filtering-version=0
      use-native-transport=true
      view-distance=10
      white-list=false
  minecraft_two_config:
    content: |
      accepts-transfers=false
      allow-flight=false
      broadcast-console-to-ops=true
      broadcast-rcon-to-ops=true
      bug-report-link=
      chat-spam-threshold-seconds=10
      command-spam-threshold-seconds=10
      difficulty=easy
      enable-code-of-conduct=false
      enable-jmx-monitoring=false
      enable-query=false
      enable-rcon=false
      enable-status=true
      enforce-secure-profile=true
      enforce-whitelist=false
      entity-broadcast-range-percentage=100
      force-gamemode=false
      function-permission-level=2
      gamemode=survival
      generate-structures=true
      generator-settings={}
      hardcore=false
      hide-online-players=false
      initial-disabled-packs=
      initial-enabled-packs=vanilla
      level-name=world
      level-seed=
      level-type=minecraft\:normal
      log-ips=true
      management-server-allowed-origins=
      management-server-enabled=false
      management-server-host=localhost
      management-server-port=0
      management-server-secret=d9MEMEdjywnNDKvzmNkbrJGaiSSzJ93rimCyq2gK
      management-server-tls-enabled=true
      management-server-tls-keystore=
      management-server-tls-keystore-password=
      max-chained-neighbor-updates=1000000
      max-players=20
      max-tick-time=60000
      max-world-size=29999984
      motd=Minecraft Server Two
      network-compression-threshold=256
      online-mode=true
      op-permission-level=4
      pause-when-empty-seconds=60
      player-idle-timeout=0
      prevent-proxy-connections=false
      query.port=25565
      rate-limit=0
      rcon.password=
      rcon.port=25575
      region-file-compression=deflate
      require-resource-pack=false
      resource-pack=
      resource-pack-id=
      resource-pack-prompt=
      resource-pack-sha1=
      server-ip=
      server-port=25565
      simulation-distance=10
      spawn-protection=16
      status-heartbeat-interval=0
      sync-chunk-writes=true
      text-filtering-config=
      text-filtering-version=0
      use-native-transport=true
      view-distance=10
      white-list=false
  minecraft_three_config:
    content: |
      accepts-transfers=false
      allow-flight=false
      broadcast-console-to-ops=true
      broadcast-rcon-to-ops=true
      bug-report-link=
      chat-spam-threshold-seconds=10
      command-spam-threshold-seconds=10
      difficulty=easy
      enable-code-of-conduct=false
      enable-jmx-monitoring=false
      enable-query=false
      enable-rcon=false
      enable-status=true
      enforce-secure-profile=true
      enforce-whitelist=false
      entity-broadcast-range-percentage=100
      force-gamemode=false
      function-permission-level=2
      gamemode=survival
      generate-structures=true
      generator-settings={}
      hardcore=false
      hide-online-players=false
      initial-disabled-packs=
      initial-enabled-packs=vanilla
      level-name=world
      level-seed=
      level-type=minecraft\:normal
      log-ips=true
      management-server-allowed-origins=
      management-server-enabled=false
      management-server-host=localhost
      management-server-port=0
      management-server-secret=d9MEMEdjywnNDKvzmNkbrJGaiSSzJ93rimCyq2gK
      management-server-tls-enabled=true
      management-server-tls-keystore=
      management-server-tls-keystore-password=
      max-chained-neighbor-updates=1000000
      max-players=20
      max-tick-time=60000
      max-world-size=29999984
      motd=Minecraft Server Three
      network-compression-threshold=256
      online-mode=true
      op-permission-level=4
      pause-when-empty-seconds=60
      player-idle-timeout=0
      prevent-proxy-connections=false
      query.port=25565
      rate-limit=0
      rcon.password=
      rcon.port=25575
      region-file-compression=deflate
      require-resource-pack=false
      resource-pack=
      resource-pack-id=
      resource-pack-prompt=
      resource-pack-sha1=
      server-ip=
      server-port=25565
      simulation-distance=10
      spawn-protection=16
      status-heartbeat-interval=0
      sync-chunk-writes=true
      text-filtering-config=
      text-filtering-version=0
      use-native-transport=true
      view-distance=10
      white-list=false

minecraft.Dockerfile

FROM openjdk:28-ea

WORKDIR /app
ADD https://piston-data.mojang.com/v1/objects/823e2250d24b3ddac457a60c92a6a941943fcd6a/server.jar /app/server.jar
RUN java -Xmx4G -Xms4G -jar /app/server.jar nogui 
RUN echo eula=true > /app/eula.txt

CMD ["java", "-Xmx4G", "-Xms4G", "-jar", "/app/server.jar", "nogui"]

minecraft.lua

local function read_varint(payload, offset)
    local value = 0
    local bit_shift = 0
    local bytes_read = 0
    
    while true do
        if offset + bytes_read >= #payload then return nil, nil end
        local b = string.byte(payload, offset + bytes_read + 1)
        
        value = value + ((b & 0x7F) * (2 ^ bit_shift))
        bit_shift = bit_shift + 7
        bytes_read = bytes_read + 1
        
        if (b & 0x80) == 0 then break end
        if bytes_read >= 5 then return nil, nil end
    end
    
    return value, bytes_read
end


local function extract_mc_hostname(txn)
    local payload = txn.req:data()
    if not payload or #payload < 5 then 
        return 
    end

    local current_offset = 0
    
    local packet_len, read1 = read_varint(payload, current_offset)
    if not packet_len then return end
    current_offset = current_offset + read1
    
    if #payload < (packet_len + read1) then
        return
    end
    
    local packet_id, read2 = read_varint(payload, current_offset)
    if not packet_id or packet_id ~= 0x00 then return end
    current_offset = current_offset + read2
    
    local proto_version, read3 = read_varint(payload, current_offset)
    if not proto_version then return end
    current_offset = current_offset + read3

    local string_len, read4 = read_varint(payload, current_offset)
    if not string_len or string_len <= 0 then return end
    current_offset = current_offset + read4
    
    if current_offset + string_len > #payload then return end
    
    local hostname = string.sub(payload, current_offset + 1, current_offset + string_len)
    
    txn:set_var("txn.mc_server_name", hostname)
end

core.register_action("parse_mc_handshake", { "tcp-req" }, extract_mc_hostname)