address comments Again

internal/clients/manager.go

@@ -184,6 +184,12 @@ func (c *AdminAPIClientsManager) GatewayClients() []*adminapi.Client {
 	return lo.Values(c.readyGatewayClients)
 }
 
+// GatewayClientsToConfigure returns the gateway clients need to be configured with the new configuration
+// in sending generated configurations.
+// In DBLess mode, it returns ALL gateway clients
+// because we need to update configurations of each gateway instance.
+// In DB-backed mode, it returns ONE random gateway client
+// because we only need to send configurations to one gateway instance, and other instances could be synced from DB.
 func (c *AdminAPIClientsManager) GatewayClientsToConfigure() []*adminapi.Client {
 	c.lock.RLock()
 	defer c.lock.RUnlock()

internal/dataplane/kong_client.go

@@ -474,9 +474,11 @@ func (c *KongClient) sendOutToGatewayClients(
 		return nil, err
 	}
 
-	// After a successful configuration update in DB mode, we should propagate the SHA from
-	// the chosen client to other clients as well as they will pick the configuration from the shared database.
-	if !dataplaneutil.IsDBLessMode(c.dbmode) &&
+	// After a successful configuration update in DB mode,
+	// since only ONE gateway client is chosen to send requests and store SHA of latest configurations,
+	// we should propagate the SHA from the chosen client to other clients
+	// as well as they will pick the configuration from the shared database.
+	if dataplaneutil.DBBacked(c.dbmode) &&
 		len(gatewayClients) > 1 {
 		for _, client := range gatewayClients {
 			client.SetLastConfigSHA([]byte(shas[0]))

internal/util/dataplane/mode.go

@@ -4,3 +4,9 @@ package dataplane
 func IsDBLessMode(mode string) bool {
 	return mode == "" || mode == "off"
 }
+
+// DBBacked returns true if the gateway is DB backed.
+// reverse of IsDBLessMode for readability.
+func DBBacked(mode string) bool {
+	return !IsDBLessMode(mode)
+}