AWS re:Invent 2025 - From Zero to Millions: Building Real-Time Applications at Scale (API312)

Building Real-Time Applications at Scale with AWS AppSync Events

Challenges of Building Real-Time Applications

• Building real-time applications involves complex challenges:
  • Monitoring application logic, databases, caching, etc.
  • Handling real-time data updates and events
  • Scaling to support millions of users
• Traditional approaches like polling can be inefficient at scale
• Bidirectional communication using WebSockets is more scalable, but introduces additional complexity:
  • Tracking connected users
  • Implementing fan-out to broadcast updates to many users
  • Scaling the backend infrastructure

Leveraging AWS AppSync Events

• AWS AppSync Events is a fully managed pub/sub service for building real-time APIs
• Reduces operational overhead of managing WebSockets at scale
• Provides built-in features for authorization, business logic, and scalability

Key AppSync Events Concepts

• Namespaces: Top-level organization for different types of events
• Channel Segments: Dynamically created segments within a namespace
• Publishers: Clients or backend systems that publish events
• Subscribers: Clients or backend systems that subscribe to events

Handling Player Entry at Scale

• Used API Gateway to implement rate limiting and control connection requests
  • First 2,000 requests per second allowed, remainder throttled with 429 responses
  • Clients handle retries with exponential backoff
• Leveraged API Gateway caching and direct DynamoDB integration to optimize read-heavy operations
• Persisted player join information using AppSync Events business logic in event handlers

Sending and Receiving Real-Time Updates

• Publishers (e.g. Lambda functions) send updates to namespaces/channels
• Subscribers (e.g. client applications) receive updates over persistent WebSocket connections
• Implemented authorization using IAM roles and API keys to control access

Calculating and Distributing Scores

• Asynchronous Lambda function handles score calculation and updates
  • Validates answers, updates scores in DynamoDB
  • Publishes score updates to individual user channels
• Used DynamoDB Streams and a Lambda function to efficiently publish leaderboard updates

Monitoring and Observability

• Monitored key metrics in AWS:
  • AppSync Events connection request rate and active connections
  • Lambda function invocations and concurrent executions
  • DynamoDB read/write capacity usage
• Leveraged AWS Lambda Power Tools for improved logging and metrics

Key Takeaways

• AppSync Events simplifies building real-time, bidirectional communication at scale
• Careful architectural design is crucial to handle connection management, fan-out, and scalability
• Leveraging managed services like API Gateway, DynamoDB, and Lambda can optimize performance and reduce operational overhead
• Monitoring and observability are essential for identifying bottlenecks and ensuring reliable operation

Real-World Applications

• Real-time applications are prevalent in many industries:
  • Ride-sharing apps tracking vehicle locations
  • Sports scores and betting odds updates
  • Multiplayer online games
  • Collaborative applications like document editing

The AWS AppSync Events service provides a powerful, managed solution for building these types of real-time, scalable applications, reducing the complexity of WebSocket management and enabling efficient, reliable real-time data distribution.