This paper presents four models to demonstrate the authors' techniques for optimizing software and hardware reliability for fault-tolerant distributed systems. The models help us find the optimal system structure while considering basic information on reliability and cost of the available software and hardware components. Each model is suitable for a distinct set of conditions or situations. All four models maximize reliability while meeting cost constraints. The simulated annealing optimization algorithm is selected to demonstrate system reliability optimization techniques for distributed systems because of its flexibility in applying to various problem types with various constraints, as well as its efficiency in computation time. It provides satisfactory reliability results while meeting the constraints.