Abstract
Security and scalability are core software qualities, which as non-functional aspects share certain characteristics and challenges in how they are approached during software development and operation. Based on expert interviews, this paper explores interactions and dependencies between security and scalability, as well as similarities and differences in their challenges. It concludes that the current understanding of the relationship between security and scalability is not yet mature. Further, it points to future research needs to better understand the relationship between these two quality aspects and better support practitioners in addressing security and scalability in a more integrated fashion.