Top Considerations for Building a Scalable Chat App Architecture
August 23, 2023

Matthew O'Riordan

Live chat has become an integral part of our communication landscape, serving various purposes, from connecting remote workers and providing customer support to fostering online communities. With millions of messages sent every second, ensuring reliable message delivery is crucial for chat app operators. However, building a robust chat experience that can deliver 24/7 service to a global user base presents significant architectural challenges.

Let's look at the top considerations for designing a scalable chat app architecture and the core components necessary for constructing a successful chat application.

Scaling to Meet User Demand

Chat apps operate in real time, setting high expectations for seamless message delivery. User demand can fluctuate dramatically depending on events and user routines, making it essential for chat app architectures to be highly responsive to changes in demand. Delayed or missing messages can erode user confidence, so building an architecture that can scale up and down is crucial.

Ensuring Fault Tolerance

Application failure can result from various factors, leading to degraded performance or complete downtime. To provide a reliable chat experience, it's important to design an architecture that can withstand faults. Horizontal scalability allows services to exist across multiple servers or virtual machines, ensuring redundancy and failover capabilities. In case of broader issues affecting multiple instances, running services in separate cloud regions or data centers can help overcome infrastructure outages.

Optimizing Latency and Global Reach

As chat apps expand globally, delivering a real time experience becomes more challenging due to increased latency caused by geographic dispersion. High latency can degrade the user experience, and it's crucial to minimize it. Deploying multiple copies of services in different geographical locations can help improve latency by reducing the distance between users and servers. However, managing a global network of services and routing traffic between them introduces complexity that requires careful consideration.

Message Synchronization and Queuing

To ensure a seamless chat experience, handling messages sent while participants are offline is essential. Queuing messages for later delivery and synchronizing messages across devices are challenges that require effective solutions. Logging each user's stream of messages and replaying them upon reconnection or delivering messages to the backend's chat history and sending it to the client upon reconnection are common approaches. A scalable database system plays a crucial role in storing and retrieving messages efficiently.

Choosing the Right Transport Mode

The choice of transport protocol between the chat client and server influences the performance and shape of the backend architecture. Each protocol has its advantages and limitations. For instance, WebRTC offers faster communication under ideal network conditions but requires additional logic for delivery confirmation and message ordering. WebSocket, on the other hand, uses TCP for reliable message delivery but lacks automatic recovery when connections are terminated. MQTT provides different levels of message delivery guarantees, adding latency in exchange for reliability.

Implementing Push Notifications

Push notifications are essential for notifying users of new messages and important events in real time. An effective push notification system requires tracking each user's platform and triggering notifications accordingly. Working with an intermediary service can simplify sending push notifications across multiple platforms.

Core Components of Chat App Architecture

While chat application architectures can vary, certain core components remain fundamental. These components form the backbone of a chat application's architecture, supporting features like video calling, file transfers, and integrations with third-party services. The core components are:

■ Application Server: The central component executing the application-specific logic, such as parsing commands and triggering system functionality.

■ Load Balancer: Distributes inbound traffic across available resources to ensure consistent service and handle routing complexities.

■ Streaming Event Manager: Orchestrates the flow of messages between services, ensuring reliable and efficient delivery to destination clients.

■ User Authentication and User Manager: Handles user authentication, authorization, and profile management, guarding against potential security breaches.

■ Presence: Manages user presence and status information to replicate context and enhance user interactions.

■ Media Store: Stores and delivers rich media files efficiently, often using a combination of central storage and content distribution networks (CDNs).

■ Database: Stores and queries various data types, such as chat messages, user status, and status messages.

By considering these architectural factors and leveraging the core components discussed, developers and architects can create dependable and efficient chat applications that meet the real time demands of modern users.

Matthew O'Riordan is CEO and Co-Founder of Ably
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