Reliability-Redundancy Allocation Problem (RRAP) signifies a major problem in software engineering along the pursuit of improving overall system reliability, especially with controlled redundancy degrees. Higher system reliability can have an immensely positive effect on the system’s success, this can be seen in the reduction of project risks, promotion of safety, and the assurance of business continuity. This literature review tries to investigate the existing research on RRAP optimization techniques to identify possible trends, gaps, and future directions. In addition to emphasizing the recent development in Homogeneous and Heterogeneous RRAP regarding diverse optimization methods with different evolutionary algorithms such as Swarm optimization algorithms. The literature survey conducted in this work outlines the use of benchmark problems: series, series–parallel, bridge, overspeed protection system, and the Pharmaceutical Plant. In addition, this work also demonstrates the need for paying extra attention to redundancy allocation in the design of reliable systems in various fields of applications.