vm/bootstrap.sh

@@ -198,8 +198,21 @@ setup_nftables() {
     systemctl disable --now firewalld >/dev/null 2>&1 || true
     systemctl mask firewalld >/dev/null 2>&1 || true
 
-    install -m 0600 "${STATE_DIR}/nftables/gitea.nft" /etc/sysconfig/nftables.conf
-    nft -c -f /etc/sysconfig/nftables.conf || die "nftables ruleset failed validation"
+    [[ -n "${PODMAN_SUBNET}" && -n "${PODMAN_GATEWAY}" ]] \
+        || die "podman-subnet/podman-gateway metadata missing; cannot render the ruleset"
+
+    # Validate BEFORE installing. A ruleset that fails to parse must never land
+    # in /etc/sysconfig: nftables.service would fail to load it on the next boot
+    # and the host would come up with no gitea_filter table at all.
+    local tmp
+    tmp=$(mktemp)
+    envsubst '${PODMAN_SUBNET} ${PODMAN_GATEWAY}' < "${STATE_DIR}/nftables/gitea.nft" > "${tmp}"
+    if ! nft -c -f "${tmp}"; then
+        rm -f "${tmp}"
+        die "nftables ruleset failed validation"
+    fi
+    install -m 0600 "${tmp}" /etc/sysconfig/nftables.conf
+    rm -f "${tmp}"
     systemctl enable --now nftables
     systemctl reload nftables
 

vm/nftables/gitea.nft

@@ -1,6 +1,7 @@
 #!/usr/sbin/nft -f
 #
-# Host firewall. Installed by vm/bootstrap.sh as /etc/sysconfig/nftables.conf.
+# Host firewall. Rendered by vm/bootstrap.sh into /etc/sysconfig/nftables.conf,
+# substituting ${PODMAN_SUBNET} and ${PODMAN_GATEWAY}.
 #
 # CRITICAL: this file must NEVER contain `flush ruleset`. The stock nftables
 # config ships with one, and it would wipe podman/netavark's NAT and forward
@@ -37,6 +38,14 @@ table inet gitea_filter {
 		# DHCP renewal from the GCE metadata server.
 		udp sport 67 udp dport 68 accept
 
+		# Container DNS. aardvark-dns answers on the bridge gateway, so lookups
+		# from containers terminate on the host and arrive here, not in forward.
+		# Netavark accepts them in its own table, but a packet has to survive
+		# every input-hook chain, and this one's drop policy would discard it
+		# anyway. Without this rule containers resolve nothing -- Caddy cannot
+		# reach Let's Encrypt and Gitea cannot reach webhook or mirror hosts.
+		ip saddr ${PODMAN_SUBNET} ip daddr ${PODMAN_GATEWAY} meta l4proto { tcp, udp } th dport 53 accept comment "container DNS"
+
 		# Admin SSH: IAP TCP forwarding range only. There is no other path in --
 		# the VPC firewall enforces the same restriction as the outer layer.
 		ip saddr 35.235.240.0/20 tcp dport 22 accept comment "IAP SSH"