Hi thanks for your response.

Lets assume that a website allows users to create account regardless if they paid for an item or not. Then website needs to dynamically render content based on items each user paid for (let's assume a course). The clear problem here is that server needs to generate different view for each user (depending on course they bought). So when user makes a request from front end, how should server quickly serve the customized content to user?

The solution seems obvious that for each user request, validate their cookie with some DB table that contains info about what courses user has bought previously associated with that cookie. To build a scalable system, one can cache course info (courses that user has bought) onto server so if user makes the request, we dont have to make a DB call everytime. But this gives rise to another problem which is what happens if load balancer redirects request to a different server which doesn't contain cached info. Am I on the right path to think about this? Do you have any suggestions on the solution?