feat: fail closed on nodes without host-only ports

internal/config/cell.go

@@ -114,10 +114,14 @@ type GalacticCellConfig struct {
 	// exec agent. Galactic drops traffic to them unless it is addressed to the
 	// guest's link-local address.
 	//
-	// Set it only once every node in the cell runs a Galactic that supports
-	// host-only ports. An older tap plugin ignores the list and leaves the
-	// ports open, and a newer one whose datapath is not loaded refuses the
-	// attachment.
+	// Set it only once every node in the cell runs a Galactic that installs
+	// galactic-tap-host-only. The conflist names that plugin, so a node
+	// without it fails the attachment rather than leaving the ports open, as
+	// does a node whose datapath is not loaded.
+	//
+	// Rolling a node back to a Galactic without that plugin also fails DEL
+	// for sandboxes whose conflist names it, so their teardown retries until
+	// the plugin is installed again.
 	HypervisorHostOnlyPorts []uint16 `json:"hypervisorHostOnlyPorts,omitempty"`
 }
 

internal/galactic/galactic/galactic.go

@@ -40,6 +40,11 @@ const (
 	// PluginTap is the master plugin for virtual machine guests.
 	PluginTap = "galactic-tap"
 
+	// PluginTapHostOnly is the tap plugin under the name only a node that
+	// enforces hostOnlyPorts installs, so an older node fails ADD instead of
+	// starting the guest with those ports open.
+	PluginTapHostOnly = "galactic-tap-host-only"
+
 	// PluginBGP publishes the attachment into BGP and SRv6.
 	PluginBGP = "galactic-bgp"
 
@@ -138,6 +143,9 @@ func Conflist(
 		DAN:           dan,
 		HostOnlyPorts: hostOnlyPorts,
 	}
+	if plugin == PluginTap && len(hostOnlyPorts) > 0 {
+		master.Type = PluginTapHostOnly
+	}
 	if len(addresses) > 0 {
 		master.IPAM = &IPAM{Type: PluginIPAM, Addresses: addresses}
 	}

internal/galactic/galactic/galactic_test.go

@@ -179,6 +179,13 @@ func TestConflistCarriesHostOnlyPorts(t *testing.T) {
 	if _, present := masterStanza(t, open)["hostOnlyPorts"]; present {
 		t.Errorf("attachment without host-only ports carries the field: %s", open)
 	}
+	if got := masterStanza(t, fenced)["type"]; got != PluginTapHostOnly {
+		t.Errorf("fenced attachment: plugin %v, want %q so a node that cannot enforce the ports fails ADD",
+			got, PluginTapHostOnly)
+	}
+	if got := masterStanza(t, open)["type"]; got != PluginTap {
+		t.Errorf("attachment without host-only ports: plugin %v, want %q", got, PluginTap)
+	}
 }
 
 func masterStanza(t *testing.T, raw string) map[string]any {