WebSocket for real-time communication in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Designing a scalable WebSocket architecture

You need to design a system that supports 1 million concurrent WebSocket connections for a chat application. Which architecture component is essential to handle this scale efficiently?

A Implement WebSocket connections directly on the database server.

B Use HTTP long polling instead of WebSocket to reduce server load.

C Use a single WebSocket server with multi-threading to handle all connections.

D Deploy multiple WebSocket servers behind a load balancer with sticky sessions.

💡 Hint

Think about how to distribute connections and maintain session consistency.

Multiple WebSocket servers behind a load balancer with sticky sessions allow distributing connections while ensuring messages reach the correct server maintaining session state.

🧠 Conceptual

intermediate

Understanding WebSocket handshake process

What is the main purpose of the WebSocket handshake between client and server?

A To close the HTTP connection after data transfer.

B To upgrade the HTTP connection to a persistent WebSocket connection.

C To encrypt the data transmitted over the connection.

D To authenticate the user credentials before connection.

💡 Hint

Consider what changes from HTTP to WebSocket during connection setup.

The handshake upgrades the HTTP connection to a persistent, full-duplex WebSocket connection allowing real-time communication.

❓ scaling

advanced

Handling message broadcasting in WebSocket systems

You want to broadcast messages from one client to all other connected clients in a distributed WebSocket server environment. Which approach ensures efficient and consistent message delivery?

A Use a centralized message broker like Redis Pub/Sub to distribute messages to all servers.

B Each WebSocket server broadcasts messages only to its connected clients without coordination.

C Clients send messages directly to all other clients without server involvement.

D Broadcast messages only to clients connected to the same server as the sender.

💡 Hint

Think about how to synchronize messages across multiple servers.

A centralized message broker like Redis Pub/Sub allows all WebSocket servers to receive and forward broadcast messages to their clients, ensuring consistency.

❓ tradeoff

advanced

Choosing between WebSocket and HTTP/2 for real-time updates

For a real-time dashboard showing live data updates, which tradeoff is true when choosing WebSocket over HTTP/2 server push?

A HTTP/2 server push is better for bidirectional communication than WebSocket.

B WebSocket connections are stateless and easier to scale than HTTP/2 streams.

C WebSocket provides full-duplex communication but requires more complex server management.

D HTTP/2 server push supports full-duplex communication natively without extra overhead.

💡 Hint

Consider communication direction and server complexity.

WebSocket supports full-duplex communication allowing both client and server to send messages anytime, but managing many connections is more complex than HTTP/2 streams.

❓ estimation

expert

Estimating server resources for WebSocket connections

You plan to support 500,000 concurrent WebSocket connections. Each connection uses 50 KB of memory on the server. How much total memory (in GB) is required just for maintaining these connections?

A Approximately 25 GB

B Approximately 50 GB

C Approximately 10 GB

D Approximately 5 GB

💡 Hint

Multiply connections by memory per connection and convert bytes to gigabytes.

500,000 connections * 50 KB = 25,000,000 KB = 25,000 MB = 25 GB.