Design a Scalable Real-time Instant Messaging System

Design a Massive-Scale Instant Messaging and Social Platform

Design a highly available and scalable communication system similar to WeChat. The system must support real-time 1:1 and group messaging for over 1 billion users, a social feed (Moments) with a complex social graph, and real-time presence tracking. Address the challenges of maintaining hundreds of millions of concurrent persistent connections, ensuring message delivery guarantees (no loss, correct ordering), and managing high-throughput write-heavy workloads for social updates. Discuss the trade-offs between push and pull models for feed distribution and the protocols used for mobile network resilience.

CassandraRedisKafkaWebSocketgRPCFlinkZooKeeperCDNTLSAnycast DNS

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Real-time Chat Platform Design

Design a high-scale real-time chat platform supporting millions of concurrent users. The system must handle 1-on-1 and group messaging with low latency and guarantee message persistence. Key considerations include maintaining persistent connections at scale, managing user presence (online/offline status), and designing a storage schema optimized for chronological message retrieval across multiple devices.

WebSocketsRedisCassandraKafkaJSON Web TokenLoad BalancerService DiscoveryNoSQL

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Global Instant Messaging System

Design the backend for a global instant messaging application like WhatsApp. The system must support real-time 1:1 and group chat for 500 million daily active users. Key requirements include low-latency message delivery, presence indicators (online/offline status), delivery and read receipts, and support for offline users via push notifications. Discuss how you handle millions of concurrent persistent connections, message ordering, and data persistence for high-volume writes.

WebSocketsCassandraRedisKafkaS3gRPCAPI GatewayPush Notifications

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Real-time Chat Platform Design

Design a globally scalable real-time chat system similar to WhatsApp or Slack. The system must support 100 million daily active users, 1:1 and group messaging, and real-time presence indicators. Focus on handling persistent connections at scale, ensuring high-write throughput for message history, and providing low-latency delivery across diverse geographic regions while maintaining message ordering and reliability.

WebSocketsRedisScyllaDBPostgreSQLgRPCJWTAPNsFCMNoSQL

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Scalable Real-Time Messaging System

Design a globally distributed messaging platform similar to Facebook Messenger. The system must support real-time delivery to billions of users, multimodal attachments (images/video), and seamless synchronization across multiple devices (mobile, web). Key requirements include low-latency message delivery, tracking delivery/read status, and high availability. Discuss how you handle millions of persistent connections, ensure message ordering, and manage storage for trillions of historical messages while maintaining reliability during network partitions.

WebSocketsCassandraRedisKafkaS3CDNgRPCTLSAES-256FCMAPNS

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Real-Time Chat & Presence System

Design a globally scalable real-time chat system supporting 100 million daily active users. The system must handle 1:1 and group conversations, provide persistent message history, and maintain a real-time 'online/offline' presence status. Address the challenges of maintaining millions of concurrent connections, minimizing message delivery latency, and efficiently managing the high-frequency write load associated with presence heartbeats.

WebSocketRedisCassandraKafkagRPCNoSQLPub/Sub

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Design a Scalable Real-time Messaging Platform

Design a real-time communication system similar to Discord that supports massive persistent connections (1M+ PCU), instantaneous message delivery across channels, and a scalable presence system. The system must handle 'megaservers' with hundreds of thousands of members and ensure message durability and ordering. Discuss your strategy for WebSocket management, storage selection for high-write chat logs, and the architectural trade-offs involved in presence broadcasting at scale.

ScyllaDBPostgreSQLRedisKafkaWebSocketsgRPCSnowflake IDCDN

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Real-Time Messaging System for Millions of Concurrent Users

Design a globally scalable real-time messaging application similar to WhatsApp or Slack. The system must support millions of concurrent WebSocket connections, ensure message persistence with high write throughput, and provide real-time presence tracking (online/offline status). Detail how you would handle message delivery for users who are currently offline, ensure message ordering, and scale the session management layer to handle millions of active users while maintaining low latency.

WebSocketRedisCassandraScyllaDBKafkagRPCNoSQLPub/SubJWTTLS

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Real-time Chat Platform Design

Design a real-time chat application capable of supporting 10 million daily active users and 1 million concurrent connections. The system must support instant 1-on-1 messaging, group chats with up to 500 members, and real-time user presence (online/offline status). Ensure the design addresses message persistence, low-latency delivery, and synchronization across multiple devices, while discussing the trade-offs between consistency and availability in a distributed environment.

WebSocketsCassandraRedisKafkaProtobufSnowflake IDS3JWT

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Scalable Real-time Messaging System (Slack)

Design a high-scale real-time messaging platform like Slack that supports millions of concurrent users. The system must handle private and group channels (up to 100k members), provide instant message delivery with strict ordering within channels, and track user presence (online/offline). Discuss how you would handle massive fan-out for popular channels, ensure high availability despite stateful connections, and optimize storage for billions of daily messages.

WebSocketsKafkaCassandraRedisgRPCSnowflake IDAnycast IPJWT

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Scalable Enterprise Messaging Platform (Slack-style)

Design a real-time messaging system similar to Slack that supports millions of concurrent users. The system must handle persistent 1-to-1 and group channels, real-time presence indicators, and message history search. Focus on solving the challenge of high-volume message fan-out in large channels and ensuring message ordering and low-latency delivery under peak load. Discuss trade-offs between consistency and availability in a global deployment.

WebSocketsCassandraRedisKafkaElasticsearchPostgreSQLFCMAPNSJWTPrometheusSnowflake ID

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Scalable Real-Time Messaging and Presence System

Design the core architecture for a large-scale real-time communication platform similar to Discord. The system must support millions of concurrent users across thousands of persistent 'servers' or groups. Focus on the end-to-end flow of a text message, the management of real-time user presence (online/offline status) at scale, and the persistent storage of billions of messages with low-latency retrieval. Address the challenges of 'fan-out' in large groups and the stateful nature of maintaining millions of persistent connections.

WebSocketsScyllaDBRedisPostgreSQLKafkaElixirSnowflake IDProtobufAnycast DNS

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