This question was great for a general problem solving question, not system design, not algos, but like, a problem came up in your day job, in the middle of a project, what do you do?! https://www.youtube.com/watch?v=UFc-RPbq8kg
Anndddd Lastly, this video on scaling web servers is critical for putting the whole picture together of DB sharding, load balancing, distributed caching, and how that all works together with multiple servers https://www.youtube.com/watch?v=xUumgxZ04SM&t=33s