Example of the homework for course by System Design. TinyURL is a URL shortening web service, which provides short aliases for redirection of long URLs.

• creates tiny URL from long URL
• redirects from long URL to tiny URL
• gets analytics about tiny URL clicks

• 50 000 000 DAU
• availability 99,95%
• tiny URLs are always stored
• service operation time 5 years
• each user creates one tiny URL per week
• on average, each tiny URL is accessed 20 times a day
• geo distribution is not needed
• no seasonality

For system design I have used C4 model. The C4 model was created as a way to help software development teams describe and communicate software architecture, both during up-front design sessions and when retrospectively documenting an existing codebase. It's a way to create maps of your code, at various levels of detail, in the same way you would use something like Google Maps to zoom in and out of an area you are interested in.

Level 1. System context diagram

Level 2. Core system container diagram

Level 2. Analytics system container diagram

RPS (create tiny URL):

DAU = 50 000 000
Each user creates one link per week
RPS = 50 000 000 / 86 400 / 7 ~= 82 

RPS (redirect from long URL to tiny URL):

DAU = 50 000 000
Service operation time = 5 years
Each user creates one link per week
Created links for 5 years = 50 000 000 / 7 * 365 ~= 3e9
On average, each tiny URL is accessed 20 times a day
Maximum RPS = 3e9 * 20 / 86400 ~= 700 000

Tiny URL length:

Created links for 5 years = 50 000 000 / 7 * 365 ~= 3e9
URL encoded base64 with length 5, will give ~= 916e6
URL encoded base64 with length 6, will give ~= 56e9
Tiny URL length = 6

Required memory:

Replication factor = 3
Service operation time = 5 years
Created links for 5 years = 50 000 000 / 7 * 365 ~= 3e9
Each record size for link ~= 150B
Required memory for 5 years = 3e9 * 150 * 3 ~= 1.5TB