Design a Digital Wallet Service
What is a Digital Wallet?
A digital wallet is a service that allows users to store, send, and receive money electronically without the need for physical cash or cards.
At its core, a digital wallet maintains a balance for each user and enables instant transfers between users, top-ups from external sources (bank accounts, credit cards), and withdrawals to external accounts.
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The system must ensure that every transaction is accurate, every balance is correct, and no money is ever created or lost.
Popular Examples: PayPal, Venmo, Apple Pay, Google Pay, Cash App, Paytm, Alipay
In this article, we will explore the high-level design of a digital wallet service.
This system design problem tests your understanding of distributed transactions, consistency guarantees, concurrent access handling, and financial system constraints. Unlike simple CRUD applications, digital wallets have zero tolerance for balance errors.
Let's start by clarifying the requirements.