Imagine sending a message to someone halfway across the world. What invisible forces ensure it arrives? The answer lies within WhatsApp's intricate design → The Client Side: Your Gateway to Global Chat • Millions of users access WhatsApp daily. They use various clients: mobile apps and web apps. • Each client has its own local SQLite database. This stores your chats locally, for quick access. → The Messaging Backbone: XMPP and Beyond • WhatsApp doesn't just use HTTP WebSockets. This handles media (images, videos). • The core messaging system relies on XMPP (Extensible Messaging and Presence Protocol). This handles the actual text and other messages. → The WhatsApp Server: A Distributed Masterpiece • WhatsApp employs a custom Ejabberd server. This runs on BEAM (Erlang’s virtual machine) and FreeBSD. • This server uses a powerful Mnesia database. It queues messages for efficient delivery. • Messages are only delivered once the recipient connects. This ensures that messages are received. • Once delivered and confirmed, messages are deleted from the database. This is smart data management. → Scalability and Resilience: The Secret Sauce • WhatsApp's architecture is designed for incredible scalability. It handles massive user loads. • The system is highly resilient. It recovers easily from failures and outages. This ensures continuous service. The magic of WhatsApp isn't just about sending messages. It's about building a robust, scalable, and reliable system. It's a testament to clever engineering and a deep understanding of distributed systems.