Modern societies depend increasingly on Critical Infrastructures (CIs) such as Smart Grids (SGs) or Intelligent Transportation Systems (ITSs). These in turn rely on complex monitoring and control functionalities, which themselves require capable, flexible and robust communication infrastructures. As dedicated networks and computing resources are associated with high costs and time-consuming deployment, the upcoming fifth generation of mobile communication (5G) aims to enable cloud-based shared infrastructures via Network Function Virtualization (NFV) and Software-Defined Networking (SDN). While NFV separates hardware and logical functionalities, SDN abstracts physical data packet forwarding from programmable network control tasks such as routing. Thereby so called SDN controllers are created, which simplify the integration of heterogeneous technologies and enable the flexible addition of new features. Yet, due to the controllers' centralized nature a potential single-point-of-failure is created. Thus we present a heartbeat-based approach to SDN resilience, utilizing redundant controllers to address CI communication requirements. An empirical evaluation, on the example of particularly demanding SGs traffic, illustrates reduced end-to-end failover delays, i.e. the duration cloud-driven 5G networks cannot process requests or changes.