Serial-parallel redundancy is a reliable way to ensure service and systems will be available in cloud computing. That method involves making copies of the same system or program, with only one remaining active. When an error occurs, the inactive copy can step in as a backup right away, this provides continuous performance and uninterrupted operation. This approach is called parallel redundancy, otherwise known as active-active redundancy, and its exceptional when it comes to strategy. It creates duplicates of a system or service that are all running at once. By doing this fault tolerance increases since if one copy fails, the workload can be distributed across any replica thats functioning properly. Reliability allocation depends on features in a system and the availability and fault tolerance you want from it. Serial redundancy or parallel redundancies can be applied to increase the dependability of systems and services. To demonstrate how well this concept works, we looked into fixed serial parallel reliability redundancy allocation issues followed by using an innovative hybrid optimization technique to find the best possible allocation for peak dependability. We then measured our findings against other research.

Redundancy allocation problem (RAP) has attracted many researchers in recent years as it is very important aspect in the field of reliability and system engineering. It plays an important role in high-tech industries. Present paper conducts a comprehensive literature review to classify, analyze and intercept the existing studies related to the RAP with respect to different systems, system configuration, methodology, constraints. The previous literature related to the RAP problems have been invested by the researchers such as Tillman in 1980, Kuo in 2007 and Soltani from 2000 to 2014. The objective of this paper is to cover the study over the past two decades starting from 2000.