Design Instagram - Problem Statement

Overview

Design a photo and video sharing social platform similar to Instagram where users can upload media, apply filters, follow others, and engage through likes, comments, and stories. The system should handle billions of photos and videos with high availability and low latency for global users.

Functional Requirements

Core Media Features

Photo Upload: Upload photos (up to 10 per post), max 8MB per photo
Video Upload: Upload videos up to 60 seconds, max 100MB
Image Filters: Apply filters and effects to photos before posting
Photo Editing: Crop, rotate, adjust brightness/contrast
Multiple Photos: Carousel posts with up to 10 photos/videos
Captions: Add text captions up to 2,200 characters
Hashtags: Tag posts with hashtags for discovery
Location Tags: Tag posts with geographic locations
User Tags: Tag other users in photos

Feed and Discovery

Home Feed: Personalized feed of posts from followed users
Explore Page: Discover new content based on interests
Profile Feed: View all posts from a specific user
Hashtag Feed: View all posts with specific hashtag
Location Feed: View posts from specific location
Saved Posts: Bookmark posts for later viewing
Feed Ranking: Algorithmic ranking based on engagement and relevance

Stories Feature

Story Upload: Post photos/videos that disappear after 24 hours
Story Viewing: View stories from followed users
Story Replies: Send direct messages in response to stories
Story Highlights: Save stories permanently to profile
Story Stickers: Add polls, questions, countdowns, location stickers
Story Analytics: View who watched your stories

Social Interactions

Follow/Unfollow: Follow users to see their content
Like Posts: Like photos and videos
Comment: Comment on posts with text and emojis
Share: Share posts via DM or to stories
Direct Messages: Private messaging (out of scope for initial design)
Mentions: Mention users in captions and comments
Notifications: Real-time notifications for likes, comments, follows

User Profile

Profile Information: Bio, profile picture, website link
Profile Grid: Grid view of all user posts
Follower/Following Lists: View followers and following
Private Accounts: Approve follower requests for private accounts
Verified Accounts: Blue checkmark for verified users
Account Settings: Privacy settings, notification preferences

Content Discovery

Search: Search for users, hashtags, locations
Trending Hashtags: Popular hashtags and topics
Suggested Users: Recommendations for users to follow
Related Posts: Similar content recommendations
IGTV: Long-form video content (10-60 minutes)
Reels: Short-form video content (15-90 seconds)

Non-Functional Requirements

Performance Requirements

Photo Upload: <5 seconds for photos <5MB
Video Upload: <30 seconds for videos <50MB
Feed Load Time: <1 second for initial 20 posts
Image Load Time: <500ms for compressed images
Story Load Time: <800ms for story feed
Search Response: <300ms for search queries
Notification Delivery: <2 seconds for real-time notifications

Scalability Requirements

Registered Users: 2 billion registered users
Daily Active Users: 500 million DAU
Monthly Active Users: 1.5 billion MAU
Photos Uploaded: 100 million photos per day
Videos Uploaded: 50 million videos per day
Stories Posted: 500 million stories per day
Feed Requests: 50 billion per day
Concurrent Users: 100 million concurrent users

Reliability Requirements

System Uptime: 99.95% availability (4.38 hours downtime per year)
Data Durability: 99.999999999% (11 9's) for media files
Upload Success Rate: 99.9% successful uploads
Disaster Recovery: <4 hours RTO, <1 hour RPO
Graceful Degradation: Maintain core features during partial outages
Zero-Downtime Deployments: Rolling updates without interruption

Security Requirements

Authentication: OAuth 2.0, JWT tokens, optional 2FA
Authorization: Role-based access control for content
Data Encryption: All data encrypted at rest (AES-256) and in transit (TLS 1.3)
Privacy Compliance: GDPR, CCPA compliance
Content Moderation: Automated and manual content review
Copyright Protection: DMCA compliance, content ID matching
Account Security: Suspicious login detection, account recovery

Consistency Requirements

Feed Delivery: Eventual consistency (5-10 second lag acceptable)
Like Counts: Eventually consistent engagement metrics
Follower Counts: Eventually consistent counts
User Profile: Strong consistency for profile updates
Story Expiration: Eventually consistent (stories may appear briefly after 24h)
Content Deletion: Eventually consistent deletion across CDN

Scale Estimates

User Metrics

Total Users: 2 billion registered users
Daily Active Users: 500 million (25% of registered)
Monthly Active Users: 1.5 billion (75% of registered)
Average Followers: 150 followers per user
Power Users: 2% of users have >100K followers
Celebrity Users: 50,000 users with >1M followers

Content Metrics

Photos per Day: 100 million photos
Videos per Day: 50 million videos
Stories per Day: 500 million stories
Comments per Day: 1 billion comments
Likes per Day: 4 billion likes
Average Photo Size: 2MB (original), 200KB (compressed)
Average Video Size: 20MB (original), 5MB (compressed)

Traffic Metrics

Feed Requests: 50 billion per day (~580K per second)
Photo Views: 100 billion per day
Video Views: 20 billion per day
Story Views: 10 billion per day
Search Queries: 2 billion per day
Read:Write Ratio: 500:1 (extremely read-heavy)

Storage Estimates

Photos (5 years):
100M photos/day × 365 days × 5 years × 2MB = 365PB (original)
100M photos/day × 365 days × 5 years × 200KB = 36.5PB (compressed)

Videos (5 years):
50M videos/day × 365 days × 5 years × 20MB = 1,825PB (original)
50M videos/day × 365 days × 5 years × 5MB = 456PB (compressed)

Stories (30 days retention):
500M stories/day × 30 days × 2MB = 30PB

Total Storage: ~2,700PB (with compression and deduplication: ~900PB)

Bandwidth Estimates

Ingress:
- Photos: 100M × 2MB = 200TB/day = 2.3GB/s
- Videos: 50M × 20MB = 1PB/day = 11.6GB/s
- Total: ~14GB/s average, ~40GB/s peak

Egress:
- Photo views: 100B × 200KB = 20PB/day = 231GB/s
- Video views: 20B × 5MB = 100PB/day = 1,157GB/s
- Total: ~1,400GB/s average, ~4,000GB/s peak
- With CDN (90% hit rate): Origin serves ~140GB/s

Edge Cases and Constraints

High-Resolution Media

Challenge: Users upload 4K photos and 4K videos
Impact: Massive storage and bandwidth requirements
Solution: Compress and transcode to multiple resolutions
Approach: Store original + multiple compressed versions

Viral Content

Challenge: Post goes viral with millions of views
Impact: Sudden traffic spike, CDN cache misses
Solution: Aggressive CDN caching, edge computing
Approach: Pre-warm cache for trending content

Celebrity Posts

Challenge: Celebrity with 200M followers posts photo
Impact: Fan-out explosion, notification storm
Solution: Separate handling for celebrity accounts
Approach: Pull-based feed for celebrities, rate-limited notifications

Story Expiration

Challenge: Stories must disappear exactly after 24 hours
Impact: Scheduled deletion at scale
Solution: Background job with eventual consistency
Approach: Mark expired, lazy deletion, CDN cache invalidation

Duplicate Content Detection

Challenge: Users re-upload same photo multiple times
Impact: Wasted storage and bandwidth
Solution: Perceptual hashing and deduplication
Approach: Hash images, detect duplicates, store once

Copyright Infringement

Challenge: Users upload copyrighted content
Impact: Legal liability, DMCA takedowns
Solution: Content ID matching, automated detection
Approach: Hash-based matching, ML-based detection

Success Metrics

User Engagement

Daily Active Users: Target 500 million DAU
Photos Uploaded: 100+ million per day
Stories Posted: 500+ million per day
Session Duration: Average 30+ minutes per session
Retention Rate: 90%+ day-1 retention, 75%+ day-30 retention
Engagement Rate: 60%+ of users engage daily (like, comment, share)

Performance Metrics

Upload Success Rate: 99.9%+ successful uploads
Feed Load Time: 95th percentile <1 second
Image Load Time: 95th percentile <500ms
Video Playback: 99%+ successful video plays
Search Performance: 95th percentile <300ms
Notification Delivery: 95%+ delivered within 2 seconds

Business Metrics

Revenue per User: Increase through ads and shopping
Ad Engagement: 3%+ click-through rate on ads
Shopping Conversion: 5%+ conversion on product tags
Support Ticket Volume: <0.05% of DAU requiring support
Infrastructure Cost: <$0.15 per user per month
Content Moderation: <0.5% of content requiring manual review

Technical Metrics

System Uptime: 99.95%+ availability
CDN Hit Rate: >90% for media content
Database Query Latency: <10ms p95
Cache Hit Rate: >85% for feed requests
Error Rate: <0.1% of requests result in errors
Deployment Frequency: Multiple deployments per day

Out of Scope

Features Not Included in Initial Design

Direct Messages: Private messaging system (separate design)
Instagram Shopping: E-commerce integration and checkout
Instagram Live: Live video streaming
Instagram TV (IGTV): Long-form video platform
Reels: Short-form video feature (TikTok competitor)
Ads Platform: Advertising creation and campaign management
Creator Studio: Analytics and management tools for creators
Business Accounts: Advanced analytics and insights
Instagram API: Third-party developer platform
Cross-posting: Integration with Facebook, Twitter

This problem statement provides the foundation for designing a comprehensive photo and video sharing platform that can compete with Instagram while maintaining high performance, reliability, and user satisfaction.