Describe the functional and non-functional requirements for a scalable messenger.

Functional Requirements:

• User registration and authentication.
• Sending and receiving messages in real-time.
• Support for personal and group chats.
• Storage of message history.
• Notifications for new messages.
• Ability to send multimedia files.
• User status (online/offline).
• Support for different platforms (mobile, web).

Non-Functional Requirements:

• Scalability: the system should operate efficiently as the number of users and messages grows.
• High availability and fault tolerance.
• Low message delivery latency.
• Security: message encryption, user data protection.
• Performance: minimal response time.
• Ease of maintenance and updates.
• Logging and monitoring for quick problem detection.

Architectural approach example: use of microservices, message brokers (e.g., Kafka, RabbitMQ) for message processing, distributed data storage, caching to speed up access.