overview.md

Backend Overview

Architecture

HTTP API Gateway routes to three Lambda functions:

• LinkHandlerFunction for create, metadata read, partial update, delete.
• RedirectFunction for public redirect and analytics increment.
• StatsFunction for summary and daily analytics read.

All functions use a single DynamoDB table: UrlShortenerTable.

DynamoDB Single-Table Design

Primary Key

• PK (string)
• SK (string)

Entity: Link

• PK = LINK#{shortCode}
• SK = METADATA

Attributes:

• originalUrl
• createdAt (ISO string)
• expiresAt (epoch seconds, used as DynamoDB TTL)
• passwordHash (optional, salted scrypt hash)
• clickCount (number)
• lastAccessedAt (ISO string, optional)
• entityType = LINK

Entity: Daily Stats

• PK = LINK#{shortCode}
• SK = STATS#{YYYY-MM-DD}

Attributes:

• date
• count
• entityType = DAILY_STATS

Access Patterns

• Read link metadata by PK + SK.
• Create link with conditional write to prevent collisions.
• Partial updates using dynamic UpdateExpression.
• Increment clicks using atomic counter.
• Aggregate daily counts with STATS# records.
• Query daily stats via begins_with(SK, "STATS#").

Expiration Strategy

• expiresAt is stored as epoch seconds.
• DynamoDB TTL eventually purges expired items.
• Redirect checks expiration synchronously and returns 410 Gone immediately.