I applied online. The process took 6 months. I interviewed at Max Planck Institute for Computer Science in Jan 2019
Interview
The interview process is rather simple, it wants to explore your contributions as a researcher, rather than knowing if you know everything. Generally you discuss what are your research interests, and if you are posed to a problem, you can explain how you would solve it.
Interview questions [1]
Question 1
What are your research expectations for this position?