Helpful

I am a starting to prep my next career move in software. In my last prep round, I took two Udemy courses on Kafka and Cassandra which I found very helpful for the system design round. I took those courses before studying Grokking and “Insiders Guide” and it worked out pretty well. I don’t deal with back end on my day to day job so the Kafka and Cassandra courses set me up at a good baseline. My question is: what are some other distributed back end technologies (like Kafka and Cassandra) that I can learn to prep for system design interview?