Trouble connecting to docker container over LAN

[dgeitheim]

Hello, I'm new to VMs/containers/networking but trying to figure things out.

Running on MacOS (M4 + Tahoe 26.1)

I have a docker-compose file like so:

services:
  mc:
    image: itzg/minecraft-server:stable
    pull_policy: daily
    tty: true
    stdin_open: true
    ports:
      - 25565:25565
    environment:
      EULA: "TRUE"
    volumes:
      # attach the relative directory 'data' to the container's /data path
      - ./data:/data

  test:
    image: nginxdemos/hello
    ports:
      - 25566:80

The two services run images that I found online, the popular itzg/minecraft-server and a test webpage demo. And the configs in the docker-compose file are basically just the default example provided in the documentation.

Ultimately, my goal is to have the services/containers I'm hosting available over the internet, but for now I'm just trying to get it to work over LAN. So I am testing with 2 computers (M4 Pro MBP and M4 Mac Mini).

On both computers I have ran:

> colima start
> docker-compose up -d

And I have verified that things are up and running with:

> docker-compose logs -f
> docker-compose ps

I have found that the local ip addresses are:
MBP: 192.168.0.10
Mini: 192.168.0.22

My issue:
✅ If I open a web browser on MBP and go to 192.168.0.22:25566, I successfully see the nginx demo site that the mini is hosting.
🟥 If I open Minecraft on MBP and "Direct connect" to 192.168.0.22:25565 it does not connect
✅ If I open Minecraft on Mini and go "direct connect" to 192.168.0.10:25565 it DOES connect (weird?)

✅ Testing localhost works as expected (on either machine, localhost:25566 shows the nginx demo and localhost:25565 connects to the Minecraft server.

I am confused why I can't connect to the Minecraft server hosted on Mini, especially since I can connect to the nginx demo server (which makes me feel confident docker-compose is working). It makes it even weirder to me that I can connect from Mini to the mc server hosted on MBP, because before I thought maybe the issue was related to a network firewall or something... Idk to be honest.

Additional details:
When running docker-compose logs -f, I can see logs related to network connection to the nginx demo. However, for the mc server I see logs related to the server starting up, bug no logs at all in response to me attempting to direct connect. My takeaway from this is that any network communication is not reaching the docker container.

Anyway, I don't really know what tools I can use to debug, which I would love to receive advice about. I tried colima ssh and then tried to run some random network commands (such as nc, tcpdump, etc... not sure if they are even relevant but I am new to this sort of thing) and I always got bash: <>: command not found.

So I guess I would be super appreciative if anyone could provide me with:

• advice specific to getting my server to work over LAN
• general advice on how to debug with colima ssh (or the proper way to do this)
• a way to see listen for packets/communications to the port that I'm hosting the server on
• open to any other suggestions or resources

Thanks!

[abiosoft]

Can you share the output of docker ps?

[dgeitheim]

dgeitheim@mini mc_server % colima start
INFO[0000] starting colima                              
INFO[0000] runtime: docker                              
INFO[0001] starting ...                                  context=vm
INFO[0012] provisioning ...                              context=docker
INFO[0013] starting ...                                  context=docker
INFO[0013] done                                         

dgeitheim@mini mc_server % docker-compose ps     
NAME      IMAGE     COMMAND   SERVICE   CREATED   STATUS    PORTS

dgeitheim@mini mc_server % docker-compose up -d  
[+] up 19/21
[+] up 22/22g/minecraft-server:stable [⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿] 226.4MB / 231.1MB Pulling                                                                                                                43.8s 
 ✔ Image itzg/minecraft-server:stable Pulled                                                                                                                                                          43.8s 
   ✔ 3c932bb5d899                     Pull complete                                                                                                                                                    0.3s 
   ✔ 2bb44d63cf15                     Pull complete                                                                                                                                                    3.8s 
   ✔ 35836319491a                     Pull complete                                                                                                                                                    0.5s 
   ✔ 1a3695062859                     Pull complete                                                                                                                                                    5.1s 
   ✔ 42b6325e5881                     Pull complete                                                                                                                                                    0.6s 
   ✔ 07a051e91219                     Pull complete                                                                                                                                                    5.1s 
   ✔ 9d59581e9b7c                     Pull complete                                                                                                                                                    0.8s 
   ✔ 3965c38db92a                     Pull complete                                                                                                                                                    3.9s 
   ✔ baf58d5fcfd7                     Pull complete                                                                                                                                                    0.6s 
   ✔ ec6632f11bbf                     Pull complete                                                                                                                                                    5.5s 
   ✔ aceb0014ef05                     Pull complete                                                                                                                                                    0.6s 
   ✔ ecf952c1944b                     Pull complete                                                                                                                                                   42.2s 
   ✔ 3fac51a59b62                     Pull complete                                                                                                                                                    0.9s 
   ✔ 5f170c2d5ee5                     Pull complete                                                                                                                                                   42.3s 
   ✔ de6a8749bef9                     Pull complete                                                                                                                                                    1.1s 
   ✔ c388039bea8c                     Pull complete                                                                                                                                                    0.4s 
   ✔ 39e9e0512242                     Pull complete                                                                                                                                                    0.8s 
   ✔ 087aca563e47                     Pull complete                                                                                                                                                   41.9s 
   ✔ b049cf0600e3                     Pull complete                                                                                                                                                   42.0s 
   ✔ 4f4fb700ef54                     Pull complete                                                                                                                                                    0.1s 
 ✔ Container mc_server-mc-1           Recreated                                                                                                                                                        0.1s 

dgeitheim@mini mc_server % docker-compose ps   
NAME               IMAGE                          COMMAND                  SERVICE   CREATED          STATUS                    PORTS
mc_server-mc-1     itzg/minecraft-server:stable   "/image/scripts/start"   mc        25 seconds ago   Up 24 seconds (healthy)   0.0.0.0:25565->25565/tcp, [::]:25565->25565/tcp
mc_server-test-1   nginxdemos/hello               "/docker-entrypoint.…"   test      9 days ago       Up 24 seconds             0.0.0.0:25566->80/tcp, [::]:25566->80/tcp

dgeitheim@mini mc_server % 

[dgeitheim]

I did a little more experimenting, maybe this is relevant:

Logs are from the host machine:
(host LAN IP=192.168.0.25, other computer LAN IP=192.168.0.10)

Test:

• start tcpdump listening to activity on port 25565 (mc server docker container)
• on other machine attempt to connect to the server (through minecraft client)
• no activity seen, ctrl-c to end tcpdump
• start tcpdump listening to activity on port 25566 (nginx demo)
• on other machine, in safari go to 192.168.0.25:25566
• see activity in tcpdump

-> why would one port be working as expected but not the other?

dgeitheim@mini mc_server % ipconfig getifaddr en1                        
192.168.0.25

dgeitheim@mini mc_server % sudo tcpdump -i any port 25565
tcpdump: data link type PKTAP
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on any, link-type PKTAP (Apple DLT_PKTAP), snapshot length 524288 bytes
^C
0 packets captured
659 packets received by filter
0 packets dropped by kernel

dgeitheim@mini mc_server % sudo tcpdump -i any port 25566
tcpdump: data link type PKTAP
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on any, link-type PKTAP (Apple DLT_PKTAP), snapshot length 524288 bytes
12:15:46.055529 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [S], seq 2134093976, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1889917146 ecr 0,sackOK,eol], length 0
12:15:46.055921 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [S.], seq 3053573314, ack 2134093977, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1013904412 ecr 1889917146,sackOK,eol], length 0
12:15:46.062995 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [.], ack 1, win 2058, options [nop,nop,TS val 1889917170 ecr 1013904412], length 0
12:15:46.062996 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [P.], seq 1:386, ack 1, win 2058, options [nop,nop,TS val 1889917171 ecr 1013904412], length 385
12:15:46.063025 IP 192.168.0.10.63420 > 192.168.0.25.25566: Flags [S], seq 1362869555, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1381185816 ecr 0,sackOK,eol], length 0
12:15:46.063107 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], ack 386, win 2053, options [nop,nop,TS val 1013904420 ecr 1889917171], length 0
12:15:46.063359 IP 192.168.0.25.25566 > 192.168.0.10.63420: Flags [S.], seq 2569187442, ack 1362869556, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 2681218523 ecr 1381185816,sackOK,eol], length 0
12:15:46.066846 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 1:1449, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066847 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 1449:2897, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066849 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 2897:4345, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066851 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 4345:5793, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066853 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 5793:7241, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066854 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 7241:8689, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066856 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 8689:10137, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066857 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], seq 10137:11585, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 1448
12:15:46.066902 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [P.], seq 11585:11813, ack 386, win 2053, options [nop,nop,TS val 1013904423 ecr 1889917171], length 228
12:15:46.066945 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [P.], seq 11813:12348, ack 386, win 2053, options [nop,nop,TS val 1013904424 ecr 1889917171], length 535
12:15:46.068278 IP 192.168.0.10.63420 > 192.168.0.25.25566: Flags [.], ack 1, win 2058, options [nop,nop,TS val 1381185823 ecr 2681218523], length 0
12:15:46.068364 IP 192.168.0.25.25566 > 192.168.0.10.63420: Flags [.], ack 1, win 2059, options [nop,nop,TS val 2681218528 ecr 1381185823], length 0
12:15:46.077662 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [.], ack 2897, win 2013, options [nop,nop,TS val 1889917182 ecr 1013904423], length 0
12:15:46.077663 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [.], ack 7241, win 1980, options [nop,nop,TS val 1889917182 ecr 1013904423], length 0
12:15:46.077663 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [.], ack 12348, win 1968, options [nop,nop,TS val 1889917184 ecr 1013904424], length 0
12:15:46.077663 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [.], ack 12348, win 2048, options [nop,nop,TS val 1889917184 ecr 1013904424], length 0
12:16:15.416354 IP 192.168.0.10.63420 > 192.168.0.25.25566: Flags [F.], seq 1, ack 1, win 2058, options [nop,nop,TS val 1381214852 ecr 2681218528], length 0
12:16:15.416367 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [F.], seq 386, ack 12348, win 2048, options [nop,nop,TS val 1889946207 ecr 1013904424], length 0
12:16:15.416476 IP 192.168.0.25.25566 > 192.168.0.10.63420: Flags [.], ack 2, win 2059, options [nop,nop,TS val 2681247876 ecr 1381214852], length 0
12:16:15.416545 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [.], ack 387, win 2053, options [nop,nop,TS val 1013933773 ecr 1889946207], length 0
12:16:15.418303 IP 192.168.0.25.25566 > 192.168.0.10.63420: Flags [F.], seq 1, ack 2, win 2059, options [nop,nop,TS val 2681247878 ecr 1381214852], length 0
12:16:15.418438 IP 192.168.0.25.25566 > 192.168.0.10.63419: Flags [F.], seq 12348, ack 387, win 2053, options [nop,nop,TS val 1013933775 ecr 1889946207], length 0
12:16:15.456695 IP 192.168.0.10.63420 > 192.168.0.25.25566: Flags [R.], seq 2, ack 1, win 2058, length 0
12:16:15.456706 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [R.], seq 387, ack 12348, win 2048, length 0
12:16:15.651743 IP 192.168.0.10.63420 > 192.168.0.25.25566: Flags [R], seq 1362869557, win 0, length 0
12:16:15.651746 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [R], seq 2134094363, win 0, length 0
12:16:15.652327 IP 192.168.0.10.63420 > 192.168.0.25.25566: Flags [R], seq 1362869557, win 0, length 0
12:16:15.661770 IP 192.168.0.10.63419 > 192.168.0.25.25566: Flags [R], seq 2134094363, win 0, length 0

[dgeitheim]

Ok, I have figured it out 🤦

It was an issue with my system settings on the client computer, nothing wrong with the host.
I had to enable:
System Settings > Privacy & Security > Local Network > Minecraft

The toggle was off, presumably because I denied access over a year ago whenever I set up the computer. Annoying that it wasn't immediately obvious that the traffic was being blocked, but maybe I should have known to check that first (it was a pretty strong clue that I could reach one service but not the other).

Anyway, thanks for maintaining Colima! And sorry for this discussion not being totally related to Colima in the end :)