OpenFaaS is a framework and infrastructure preparation system for building serverless applications. It originated from the serverless framework in the Docker Swarm and now supports other kinds of infrastructure backends, such as Kubernetes or Hyper.sh. Functions in OpenFaaS are containers. Any program written in any language can be packed as a function by leveraging the container technologies of Docker. This enables us to fully reuse the existing code to consume a wide range of web service events without rewriting the code. OpenFaaS is a great tool for modernizing old systems to run on a cloud-based infrastructure.