System design rounds are my favorite by far, on both sides of the interview. If you're someone who likes browsing a lot of the engineering blog posts that come

System design rounds are my favorite by far, on both sides of the interview. If you're someone who likes browsing a lot of the engineering blog posts that come across HN, reddit, etc, there is a treasure trove of questions to be had. Just look up a large company tech blog and read through one of their articles. Whether it's well written (you get to learn a lot from the trenches) or not (you have to think about the gaps that aren't explained) you win. One thing I like to do is take a post-mortem or breakdown of a service (say messaging at slack, which has quite a few blogposts about it), read until they say "since we did not have X as a constraint", then mentally rewrite the rest of the article with that constraint put in. One can usually find tons of these implicitly, or some explicitly stated. Depending on the technology, you can also search specific forums to see other problems that things run into at scale. Which leads me to another fun source of system design problems: * Find people talking about pushing the bounds of configuration values in production. There are a _ton_ of config values in many pieces of software. Go check the software forums to see why the heck someone would be setting the value so high/low/strangely. An example of this are the elasticsearch or kafka forums. Find someone storing lots of very small things in elasticsearch and hitting scaling issues, or someone trying to maximize storing some very large things, and how they work around it.