The Network Functions Virtualization (NFV) paradigm revolutionizes networking technology by enabling the installation of software processes as service functions on general-purpose servers. Through NFV, a Service Graph is created, offering improved flexibility and performance by enabling multiple paths between endpoints. However, the manual creation and configuration of Service Graphs, especially when it involves security functions, present challenges. Security functions, such as firewalls and parental controls, play a crucial role in ensuring network safety. Misconfigurations and delays in updating security defenses to meet evolving security requirements are common risks associated with manual operations. To overcome these challenges, this thesis contributes to the development of VEREFOO (VErified REFinement and Optimized Orchestration).