Requirements clarification: Making sure we have all the information before starting. This may include how many requests or users we are expecting.

Back of the envelope estimation: Doing some quick calculations to gauge the necessary system performance. For example, how much storage or bandwidth do we need?

System interface design: What will our system look like from the outside, how will people interact with it? Generally this is the API contract.

Data model design: What our data will look like when we store it. At this point we could be thinking about relational vs non-relational models.

Logical design: Fitting it together in a rough system! At this point I’m thinking at a level of ‘how would I explain my idea to someone who knows nothing about tech?’

Physical design: Now we start worrying about servers, programming languages and the implementation details. We can superimpose these on top of the logical design.

Identify and resolve bottlenecks: At this stage we will have a working system! We now refine the design.

https://medium.com/double-pointer/system-design-interview-video-streaming-service-e-g-netflix-or-youtube-design-adc2402e54a1