fix: use Dappnode DNS and correct CoreDNS port detection

docker-compose.yml

@@ -5,6 +5,10 @@ services:
     image: "wireguard.wireguard.dnp.dappnode.eth:0.1.1"
     container_name: DAppNodeCore-wireguard.wireguard.dnp.dappnode.eth
     restart: unless-stopped
+    # Keep Docker aliases while using Dappnode DNS for external lookups.
+    dns:
+      - 172.33.1.2
+      - 10.20.0.2
     cap_add:
       - NET_ADMIN
       - SYS_MODULE

readme-vars.yml

@@ -158,6 +158,7 @@ init_diagram: |
   "wireguard:latest" <- Base Images
 # changelog
 changelogs:
+  - {date: "24.10.26:", desc: "Use Dappnode DNS upstreams and ignore outgoing DNS sockets when detecting CoreDNS port conflicts."}
   - {date: "24.01.26:", desc: "Rebase to Alpine 3.23 again as openresolv alpine 3.23 package has now been updated."}
   - {date: "22.01.26:", desc: "Revert to Alpine 3.22 due to resolvconf bug."}
   - {date: "04.01.26:", desc: "Rebase to Alpine 3.23."}

root/etc/s6-overlay/s6-rc.d/svc-coredns/run

@@ -1,7 +1,7 @@
 #!/usr/bin/with-contenv bash
 # shellcheck shell=bash
 
-if netstat -apn | grep -q ":53 " && [[ -z "${USE_COREDNS}" ]]; then
+if netstat -lntup | grep -q ":53 " && [[ -z "${USE_COREDNS}" ]]; then
     USE_COREDNS="false"
 fi
 

tests/test_coredns_port_detection.py

@@ -0,0 +1,59 @@
+"""Exercise the image's listener guard with real sockets and no VPN state."""
+import argparse
+import json
+from pathlib import Path
+import subprocess
+import time
+import uuid
+
+parser = argparse.ArgumentParser()
+parser.add_argument('--image', required=True)
+parser.add_argument('--helper-image', default='node:22.23.4-alpine3.24')
+parser.add_argument('--output')
+args = parser.parse_args()
+name = 'wireguard-port-check-' + uuid.uuid4().hex[:10]
+holder = name + '-udp'
+
+def docker(*cmd, check=True):
+    result = subprocess.run(['docker', *cmd], capture_output=True, text=True, timeout=30)
+    if check and result.returncode:
+        raise RuntimeError('Docker ' + cmd[0] + ' failed: ' + result.stderr[-500:])
+    return result
+
+try:
+    docker('run', '-d', '--name', name, '--network', 'none', '--cpus', '1', '--memory', '256m',
+           '--entrypoint', 'sh', args.image, '-c', 'sleep infinity')
+    script = docker('exec', name, 'cat', '/etc/s6-overlay/s6-rc.d/svc-coredns/run').stdout
+    line = next(line.strip() for line in script.splitlines() if line.startswith('if netstat '))
+    guard = line.removeprefix('if ').split(' && [[', 1)[0]
+    docker('run', '-d', '--name', holder, '--network', 'container:' + name, '--cpus', '1', '--memory', '128m',
+           '--entrypoint', 'node', args.helper_image, '-e',
+           "const s=require('dgram').createSocket('udp4');s.connect(53,'127.0.0.1',()=>console.log('connected'));setInterval(()=>{},10000)")
+    for _ in range(30):
+        if 'connected' in docker('logs', holder).stdout:
+            break
+        time.sleep(.1)
+    else:
+        raise RuntimeError('UDP fixture did not become ready')
+    # Reproduce the original false positive while there is no listening server.
+    assert docker('exec', name, 'sh', '-c', 'netstat -apn | grep -q ":53 "', check=False).returncode == 0
+    assert docker('exec', name, 'sh', '-c', guard, check=False).returncode == 1, 'Outgoing DNS socket was mistaken for a listener'
+    # Then start a real listener. The same image-provided guard must detect it.
+    docker('exec', name, 'sh', '-c', "printf '.:53 {\\n    errors\\n}\\n' > /tmp/port-check-Corefile")
+    docker('exec', '-d', name, '/usr/bin/coredns', '-conf', '/tmp/port-check-Corefile')
+    for _ in range(30):
+        if docker('exec', name, 'sh', '-c', guard, check=False).returncode == 0:
+            break
+        time.sleep(.1)
+    else:
+        raise AssertionError('Actual DNS listener was not detected')
+    result = {'success': True, 'oldCheckFalsePositiveReproduced': True,
+              'outgoingDnsSocketIgnored': True, 'actualDnsListenerDetected': True,
+              'productionStateMounted': False, 'network': 'none'}
+finally:
+    docker('rm', '-f', '-v', holder, check=False)
+    docker('rm', '-f', '-v', name, check=False)
+
+if args.output:
+    Path(args.output).write_text(json.dumps(result, indent=2) + '\n')
+print(json.dumps(result, indent=2))