OpenPatch is an open platform for assessment and training of programming skills. It is currently driven by twelve microservices. The frontend microservice is implemented in React. Most backend microservices are implemented in Flask. In this session the challenges and solutions of building a microservice architecture for OpenPatch with Flask will be presented. It will be shown how authentication with JWT via a centralized authentification service is implemented, how communication between the microservices with RabbitMQ is integrated, how versioning of microservices (api-endpoints and database-schemas) is used to keep backward-compatibility and what means are set up to ease the development of new microservices. This session should provide insights in the development of a microservice architecture with Flask, which could help others developers to implement their own or to spark the discussion of best practices.