It is very likely that software running in an everchanging environment needs to evolve at multiple points during its lifecycle. Because maintenance costs money, it is important for such tasks to be as effective and efficient as possible. During the history of software development service- and microservice-based architectures have emerged among other architectures. Since these architectures promise to provide a high maintainability, many legacy systems are or were migrated towards a service- or microservice-based architecture. In order to keep such systems running, maintenance is inevitable. While a lot of research has been published regarding maintainability assurance for service-based systems, microservice-based systems have not gotten a lot of attention. All published research is spread across several scientific databases which makes it difficult to get an extensive overview of existing work. In order to provide such overview of maintainability assurance regarding service- and microservice-based systems, we conducted a systematic literature review. To support our literature review, we developed a set of meaningful research questions and a rigid research protocol. Based on our protocol we collected a set of 223 different papers. These papers were first categorized into a threefold set of categories (architectural, thematical and methodical). After that, the most relevant research directions from each thematical category were extracted and presented. Lastly, we extracted and presented notable differences between approaches relating to service-oriented architecture or microservice-based systems. Our findings show a clear underrepresentation of maintainability assurance approaches suitable for microservice-based systems. We further discovered that regarding our formed categories, we could find several research directions such as change impact in business processes in "Change Impact and Scenarios". In the end, we could identify some differences between service- and microservice-based systems concerning approaches we retrieved in this thesis. A difference, for example was that in comparison with papers related to service-oriented architecture in Äntipatterns and Bad Smells", microservices related papers only contained basic information on antipatterns, but no approaches to detect them. Due to our findings we suggest a higher participation in research regarding maintainability assurance for microservice-based systems. Possible future work in this area could include further research on the applicability of service-oriented maintainability assurance approaches or techniques in microservice-based systems. Furthermore, future researchers could conduct follow-up literature reviews and investigate topics such as runtime adaptation, testing and legacy migration, since we excluded such topics from this thesis.