[System Design] Transfer Sum

Photo by Aditya Vyas on Unsplash

Problem Description

We’d like to put up a counter of how much money has been transferred through the money-exchange APP in the past week. The purpose is to help customers trust us by showing how much volume we’re moving successfully.

Step 1: Gather Requirements

First, we need to ask the interviewer some questions to clarify the requirements. Lets imagine the answers to those questions are in italics.

Functional

• What currency should the volume be expressed in? It should be in the local currency of the user. If they’re from a US IP address, let’s give them that value in USD. If they are from France, display in Euros.
• What exchange rate to use? During time of transaction or when the APP page is loaded? Up to you.
• What is the data source? There is a Transfer Service which will produce an event whenever a transfer has been sent out, and how mich and in what currency. There is a rate service which you can use.

Non Functional

• How long should we store the data for? Can we purge data that exist for more than 1 week? Yes, don’t need to store data for more than 1 week.
• What is the expected writes and reads? More writes than read.