Performance Evaluation of RESTful APIs Under Simulated Load Conditions
Prabesh Shrestha · Theseus (Ammattikorkeakoulujen) · 2026
This thesis focuses on evaluating the performance of RESTful APIs under simulated load conditions. In modern software systems, APIs play an important role in communication between frontend and backend, but performance testing is often not given enough attention during development. This can lead to issues such as slow response times, errors, and system instability when the application is used by many users. This thesis is carried out in association with Tutors Oy, Helsinki. The software currently being developed is Burbest. The main aim is to test the backend APIs and evaluate the performance of the APIs. In the research, the concepts related to the API architecture and performance testing are studied. The testing is done using the k6 tool, which is a modern tool used for performance testing working well in a JavaScript environment. Different conditions of loading are applied to measure the response time, throughput, and error rate. The results show that the local database configuration delivers consistently low response times across all load levels, while the cloud-hosted MongoDB Atlas configuration degrades non-linearly above 30 concurrent virtual users, particularly for write operations. All tests maintained a 0% error rate. Recommendations are provided for database configuration, caching, and future testing.