  To remain competitive in a fast changing environment, many companies started
to migrate their legacy applications towards a Microservices architecture. Such
extensive migration processes require careful planning and consideration of
implications and challenges likewise. In this regard, hands-on experiences from
industry practice are still rare. To fill this gap in scientific literature, we
contribute a qualitative study on intentions, strategies, and challenges in the
context of migrations to Microservices. We investigated the migration process
of 14 systems across different domains and sizes by conducting 16 in-depth
interviews with software professionals from 10 companies. We present a separate
description of each case and summarize the most important findings. As primary
migration drivers, maintainability and scalability were identified. Due to the
high complexity of their legacy systems, most companies preferred a rewrite
using current technologies over splitting up existing code bases. This was
often caused by the absence of a suitable decomposition approach. As such,
finding the right service cut was a major technical challenge, next to building
the necessary expertise with new technologies. Organizational challenges were
especially related to large, traditional companies that simultaneously
established agile processes. Initiating a mindset change and ensuring smooth
collaboration between teams were crucial for them. Future research on the
evolution of software systems will in particular profit from the individual
cases presented.
