Design a bank account ledger service supporting deposits, withdrawals, transfers, balance queries, and transaction history. Define APIs, data model, and how to ensure ACID semantics for single-account updates and atomic multi-account transfers. Use a double-entry ledger for auditability, include idempotency and exactly-once processing, and explain concurrency control, reconciliation with external payment rails, fraud checks, limits, and dispute handling. Describe sharding, indexing, read replicas, and recovery strategies to scale and maintain consistency.

This question evaluates understanding of distributed systems, transactional databases, double-entry ledger accounting, idempotency, concurrency control, reconciliation with external payment rails, and operational concerns for financial systems.

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This is a hard difficulty System Design question, commonly asked during Take-home Project rounds at Coinbase.

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Design a bank account ledger | Coinbase Interview Question

Design a Bank Account Ledger Service

Context

You are building the core ledger service for a fintech wallet/banking platform. The service must support customer account balances with full auditability and correctness under concurrency and failures.

Functional Requirements

Deposits, withdrawals, and intra-ledger transfers
Balance queries (posted vs available)
Transaction history with pagination and filters

Non-Functional and Architectural Requirements

ACID semantics for single-account updates
Atomicity for multi-account transfers
Double-entry bookkeeping for auditability and reconciliation
Idempotency and exactly-once effect for API requests and async processing
Concurrency control under high throughput
Integration and reconciliation with external payment rails (e.g., ACH, cards)
Fraud checks, spending limits, and dispute/chargeback handling
Scalability: sharding/partitioning, indexing strategy, read replicas, caching
Recovery strategies: backups, point-in-time recovery, invariants validation

Deliverables

Describe:

Public APIs (endpoints, request/response shape, idempotency usage)
Data model (entities, relationships, constraints) using a double-entry ledger
How to ensure ACID semantics and atomic multi-account transfers
Idempotency and exactly-once processing design
Concurrency control approach
Reconciliation with external rails, fraud checks, limits, and dispute flows
Sharding, indexing, read replicas, and recovery strategies for scale and consistency

Non-Functional and Architectural Requirements

ACID semantics for single-account updates

Atomicity for multi-account transfers

Double-entry bookkeeping for auditability and reconciliation

Idempotency and exactly-once effect for API requests and async processing

Concurrency control under high throughput

Integration and reconciliation with external payment rails (e.g., ACH, cards)

Fraud checks, spending limits, and dispute/chargeback handling

Scalability: sharding/partitioning, indexing strategy, read replicas, caching

Recovery strategies: backups, point-in-time recovery, invariants validation

Deliverables

Describe:

Public APIs (endpoints, request/response shape, idempotency usage)

Data model (entities, relationships, constraints) using a double-entry ledger

How to ensure ACID semantics and atomic multi-account transfers

Idempotency and exactly-once processing design

Concurrency control approach

Reconciliation with external rails, fraud checks, limits, and dispute flows

Sharding, indexing, read replicas, and recovery strategies for scale and consistency

Design a bank account ledger

Quick Overview

Design a Bank Account Ledger Service

Context

Functional Requirements

Non-Functional and Architectural Requirements

Deliverables

Solution

Comments (0)

Design a bank account ledger

Quick Overview

Design a Bank Account Ledger Service

Context

Functional Requirements

Non-Functional and Architectural Requirements

Deliverables

Solution

Comments (0)