zones: allow RingInfo.Merge() to enable, but not disable

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/zones/rings.go

@@ -31,9 +31,9 @@ func (ri *RingInfo) Merge(alter *RingInfo) error {
 	case ri.Ring != alter.Ring:
 		// different ring
 		return fmt.Errorf("invalid %s: %v ≠ %v", "ring", ri.Ring, alter.Ring)
-	case ri.Enabled != alter.Enabled:
-		// different state
-		return fmt.Errorf("invalid %s: %v ≠ %v", "enabled", ri.Enabled, alter.Enabled)
+	case ri.Enabled && !alter.Enabled:
+		// can't disable via Merge
+		return fmt.Errorf("invalid %s: %v → %v", "enabled", ri.Enabled, alter.Enabled)
 	case !canMergeAddress(ri.Address, alter.Address):
 		// different address
 		return fmt.Errorf("invalid %s: %v ≠ %v", "address", ri.Address, alter.Address)
@@ -42,6 +42,15 @@ func (ri *RingInfo) Merge(alter *RingInfo) error {
 		return fmt.Errorf("invalid %s: %s ≠ %s", "keys", ri.Keys, alter.Keys)
 	}
 
+	return ri.unsafeMerge(alter)
+}
+
+func (ri *RingInfo) unsafeMerge(alter *RingInfo) error {
+	// enable via Merge
+	if alter.Enabled {
+		ri.Enabled = true
+	}
+
 	switch {
 	case ri.Keys == nil:
 		// assign keypair