Solution

It was found (here, and here) that Podman uses its own DNS server, aardvark-dns which is bound to port 53 (this explains why I was able to bind to 53 with nc on the host while the container would still fail). So the solution is to bridge the network for that port. So, in the compose file, the ports section would become:

ports:
  - "<host-ip>:53:53/tcp"
  - "<host-ip>:53:53/udp"
  - "80:80/tcp"

where <host-ip> is the ip of the machine running the container — e.g. 192.168.1.141.

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Original Post

I so desperately want to bash my head into a hard surface. I cannot figure out what is causing this issue. The full error is as follows:

Error: cannot listen on the UDP port: listen udp4 :53: bind: address already in use

This is my compose file:

version: "3"
services:
  pihole:
    container_name: pihole
    image: docker.io/pihole/pihole:latest
    ports:
      - "53:53/tcp"
      - "53:53/udp"
      - "80:80/tcp"
    environment:
      TZ: '<redacted>'
    volumes:
      - './etc-pihole:/etc/pihole'
      - './etc-dnsmasq.d:/etc/dnsmasq.d'
    restart: unless-stopped

and the result of # ss -tulpn:

Netid       State        Recv-Q       Send-Q                             Local Address:Port               Peer Address:Port       Process                                         
udp         UNCONN       0            0                    [fe80::e877:8420:5869:dbd9]:546                           *:*           users:(("NetworkManager",pid=377,fd=28))       
tcp         LISTEN       0            128                                      0.0.0.0:22                      0.0.0.0:*           users:(("sshd",pid=429,fd=3))                  
tcp         LISTEN       0            128                                         [::]:22                         [::]:*           users:(("sshd",pid=429,fd=4))        

I have looked for possible culprit services like systemd-resolved. I have tried disabling Avahi. I have looked for other potential DNS services. I have rebooted the device. I am running the container as sudo (so it has access to all ports). I am quite at a loss.

• Raspberry Pi Model 1 B Rev 2
• Raspbian (bookworm)
• Kernel v6.6.20+rpt-rpi-v6
• Podman v4.3.1
• Podman Compose v1.0.3

EDIT (2024-03-14T22:13Z)

For the sake of clarity, # netstat -pna | grep 53 shows nothing on 53, and # lsof -i -P -n | grep LISTEN shows nothing listening to port 53 — the only listening service is SSH on 22, as expected.

Also, as suggested here, I tried manually binding to port 53, and I was able to without issue.