Your hardest task
Write it in your own words, from your own experience. It stays in this browser only.
Answer out loud or in your head first, then compare.
Answer
Talk about one specific task and why it was hard: unclear requirements, scale, an outage or unfamiliar technology.
How to structure the answer: Go from the risk and the options you considered to the implementation and how you verified it. The result can be qualitative if you don't have reliable numbers.
Practical note: Don't equate difficulty with the number of tools used. What matters most is how you went about solving the problem.
This is a structure for preparing your own answer, not a ready-made story about your experience.
Could you give this answer in an interview today?