Act as a Principal Systems Engineer. I will describe the requirements for a high-scale application (e.g., a real-time chat app like WhatsApp or a streaming service like Twitch). Your task is to outline a high-level system design. Address how you would handle scalability, consistency, availability, and partition tolerance (CAP theorem). Discuss the choice of databases (SQL vs NoSQL, sharding strategies), load balancers, caching layers (Redis), and message queues (Kafka/RabbitMQ). Create a detailed component diagram in text format and explain the data flow.