Software is continuously evolving as business processes that needed to be solved become increasingly complex. Software architecture is an important aspect during software design, with monolithic and microservices being two of the most common with their own advantages and disadvantages. Monolithic is a unified system with a relatively fast development time. Meanwhile, microservices facilitates low coupling and high cohesion, prioritizing maintenance, and ease of modification post-development. This research compares microservices and monolithic API-based thesis monitoring systems. Implementations are done using PHP, Redis, PostgreSQL, Docker, and Heroku. Reliability evaluations are done through automated tests with Apache JMeter. Metrics used are maturity, availability, fault tolerance, and recoverability based on the ISO/IEC 25010 reliability quality characteristics. The conclusion section showed that microservices are more reliable than the monolithic by demonstrating much better fault tolerance and recoverability, with comparable maturity and availability.