Scaling Serverless Functions: Horizontal or Vertical? Both!

The Function-as-a-Service (FaaS) execution model has dominated cloud computing [1-6]. FaaS applications are developed as standalone functions for which users provide the source code, while providers secure the dependencies (e.g., runtime) and the necessary resources (e.g., memory, CPU) for their execution. This simplifies programming, i.e. developers are alleviated from the burden to manage an entire system, and enables better resource management, i.e. providers can scale dynamically and transparently the resources allocated per function based on the incoming load of requests. Typically, resource allocation is controlled by increasing or decreasing the number of function instances that serve requests.