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I made a deal with my son where in, if he built a fully-working, 3 way traffic light in minecraft, I would host him his own minecraft server so he and his friends could play anytime. He upheld his end of the bargain, so it's my turn.

In order to keep this thing boxed in, and trying to keep it both simple and cheap for his friends (mojang auth requires paid mojang account), I am using a simple VPN container with shared users/pass/psk - he can just give it to his friends.

The problem: This works fine if, when they connect they set the server to be the ip address of the container on the docker network. Problem is, that changes every time I restart. I need a DNS resolver so that the server name is always minecraft when on the vpn. The DNS that comes with this VPN uses public DNS, which I can override, but when I dig while on the vpn container (but not on the vpn iself) I get an ip address I didn't expect and one I simply can't predict. Thus, I don't know if/how I should override it. I have read the documentation on docker's website and I have also considered using dnsmasq as a forwarder. Details below.

docker-compose.yml

version: '3.3'
services:
  minecraft:
    build:
      context: .
    restart: always
    hostname: minecraft
    volumes:
      - world:/game/world
  vpn:
    image: hwdsl2/ipsec-vpn-server
    environment:
      - VPN_DNS_SRV1=127.0.0.11
    restart: always
    hostname: vpn
    ports:
      - 500:500/udp
      - 4500:4500/udp
    privileged: true
volumes:
  world:

terminal debug (off vpn):

[ec2-user@ip-172-31-25-185 ~]$ docker ps
CONTAINER ID        IMAGE                     COMMAND                  CREATED             STATUS              PORTS                                          NAMES
608165ea8236        hwdsl2/ipsec-vpn-server   "/opt/src/run.sh"        2 days ago          Up 2 days           0.0.0.0:500->500/udp, 0.0.0.0:4500->4500/udp   mcft_vpn_1
075f6313ae9d        mcft_minecraft            "java -Xms1024M -jar…"   2 days ago          Up 2 days           25565/tcp                                      mcft_minecraft_1
[ec2-user@ip-172-31-25-185 ~]$ docker exec -it 608165ea8236 /bin/bash
root@vpn:/opt/src# dig minecraft

; <<>> DiG 9.10.3-P4-Debian <<>> minecraft
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29390
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;minecraft.         IN  A

;; ANSWER SECTION:
minecraft.      600 IN  A   172.20.0.2

;; Query time: 0 msec
;; SERVER: 127.0.0.11#53(127.0.0.11)
;; WHEN: Mon Jul 08 14:45:41 UTC 2019
;; MSG SIZE  rcvd: 52

root@vpn:/opt/src#
Christian Bongiorno
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1 Answers1

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Probably the simplest solution would be to assign a static IP address to the minecraft container. You can see how to do that in https://stackoverflow.com/questions/27937185/assign-static-ip-to-docker-container (refer to the answer which uses docker-compose, since that's what you're using).

Matt Zimmerman
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