fix(rego-tunnel): detect outbound iface for NAT

apps/rego-tunnel/build/setup-network.sh

@@ -5,6 +5,13 @@
 
 set -e
 
+# Pick the outbound interface based on the container's default route.
+# (In Docker, this is not always eth0 when multiple networks are attached.)
+WAN_IF="$(ip route show default 0.0.0.0/0 2>/dev/null | awk '{for(i=1;i<=NF;i++) if($i=="dev"){print $(i+1); exit}}')"
+if [ -z "${WAN_IF}" ]; then
+    WAN_IF="eth0"
+fi
+
 # Create bridge if not exists
 if ! ip link show br0 &>/dev/null; then
     ip link add br0 type bridge
@@ -25,7 +32,14 @@ fi
 echo 1 > /proc/sys/net/ipv4/ip_forward
 
 # Setup NAT/masquerade for outbound traffic from VM
-iptables -t nat -C POSTROUTING -s 100.100.0.0/24 -o eth0 -j MASQUERADE 2>/dev/null ||     iptables -t nat -A POSTROUTING -s 100.100.0.0/24 -o eth0 -j MASQUERADE
+iptables -t nat -C POSTROUTING -s 100.100.0.0/24 -o "$WAN_IF" -j MASQUERADE 2>/dev/null || \
+    iptables -t nat -A POSTROUTING -s 100.100.0.0/24 -o "$WAN_IF" -j MASQUERADE
+
+# Ensure forwarding between the VM bridge and outbound interface
+iptables -C FORWARD -i br0 -o "$WAN_IF" -j ACCEPT 2>/dev/null || \
+    iptables -A FORWARD -i br0 -o "$WAN_IF" -j ACCEPT
+iptables -C FORWARD -i "$WAN_IF" -o br0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT 2>/dev/null || \
+    iptables -A FORWARD -i "$WAN_IF" -o br0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
 
 # Forward traffic destined for VPN networks to VM (10.35.33.230 = IBM i)
 # The VM will route this through its VPN tunnel
@@ -39,3 +53,4 @@ echo "Network setup complete"
 echo "Bridge: br0 = 100.100.0.1/24"
 echo "TAP: tap0 attached to br0"
 echo "Route: 10.35.33.230 via 100.100.0.2 (VM)"
+echo "Outbound interface: ${WAN_IF}"