High-Level Design of Facebook Messenger

Introduction

Facebook Messenger powers real-time conversations for over 500 million active users daily. Building such a system demands expertise in scalable architectures, distributed data stores, and low-latency communication. If you’re preparing for a system design interview, our complete system design training provides hands-on projects to master these concepts.

Core Requirements and Goals

Functional Requirements

• User Management: Registration, authentication, profile updates, and contact management.
• Messaging: 1:1 and group chat support for text, images, videos, and files.
• Real‑Time Delivery: Instant message updates via persistent connections.
• Notifications: In-app and push alerts for new messages.
• End‑to‑End Security: Encryption to ensure privacy.

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Non‑Functional Requirements

• Scalability: Seamlessly handle millions of concurrent users.
• Low Latency: Deliver messages in under 100 ms.
• High Availability: Fault‑tolerant services with multi‑region failover.
• Data Consistency: Prevent message loss or duplication.
• Storage Efficiency: Optimize for petabytes of text and media.

Capacity Planning and Constraints

What traffic can Facebook Messenger handle?

Assuming 25 billion messages per day, with an average of 2.33 reads per message:

• Write Requests: 25 B
• Read Requests: 58 B
• Total Requests: 83 B per day

That translates to an average of 960 K queries per second (QPS) and a peak of approximately 4.8 M QPS.

How much storage is needed?

• Daily Text Storage: 25 TB
• Annual Text Storage: 9 PB
• 5‑Year Projection (Text + Media): 450 PB

Bandwidth and Cache Requirements

• Daily Bandwidth: 1.3 PB (text + media) ≈ 15 GB/sec
• Caching: 10 % of messages (2.5 TB) stored in Redis for hot reads, plus 5 TB for metadata/indexing.

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