Evolution of code technical debt in microservices architectures

Context: Microservices are gaining significant traction in academic research and industry due to their advantages, and technical debt has long been a heavily researched metric in software quality context. However, to date, no study has attempted to understand how code technical debt evolves in such architectures. Aim: This research aims to understand how technical debt evolves over time in microservice architectures by investigating its trends, patterns, and potential relations with microservices number. Method: We analyze the technical debt evolution of 13 open-source projects. We collect data from systems through automated source code analysis, statistically analyze results to identify technical debt trends and correlations with microservices number, and conduct a subsequent manual commit inspection. Results: Technical debt increases over time, with periods of stability. The growth is related to microservices number, but its rate is not. The analysis revealed trend differences during initial development phases and later stages. Different activities can introduce technical debt, while its removal relies mainly on refactoring. Conclusions: Microservices independence is fundamental to maintain the technical debt under control, keeping it compartmentalized. The findings underscore the importance of technical debt management strategies to support the long-term success of microservices.