lkrnac/cloudtalk-assignment

I considered this architecture:

But than found a way where I could eliminate one database and improve "caching" of average ratings:

Reasoning/explanation:

• All data are stored in single database, so that it is easier to join them

• Redis here is used as MQ (pub/sub mode) to send review calculation messages from product-service to review-calculation-service

• For average rating calculation, there is no need to have all the review present. These fields of CalculationMessage are enough:

  • averageRating;
  • originalCount;
  • countChange;
  • ratingChange;

• Final average rating is:

  newAverageRating = (averageRating * originalCount + ratingChange) / (originalCount + countChange)  
  

• review-calculation-service informs product service about new average rating via private REST endpoint

• Average rating is stored in products table

• I know there was this sentence "Product reviews and average product ratings should be cached."

  • To me storing those values in single database is far better "caching" storing them is separate in separate redis instance
  • I believe it is worth to avoid caching if possible
  • This would be faster, because I don't need to combine response from database and cache, single select is needed here

• I did not have time to figure out enum for review.rating, Nest.js stack is new to me, so I had to learn a lot on the way

• Typescript and ESLint configs were generated by Nest.js, didn't touch them

Further steps:

• Create authorization for private updateAverageRating endpoint, so that only review-calculation-service is able to call it
• Use more black box testing, that would cover also controller mappings
• Test also review-calculation-service
• Add authentication
• Tidy up URLs and env variables
• Secure postgres and redis much more
• Create Terraform orchestration, plug the project into CI/CD