Design a Distributed Message Queue

When designing a distributed message queue, consider both functional and non-functional requirements. Use a topic-based system with a pull model for scalability and control, and a key factor for sharding. Store data with SQL, NoSQL, or a write-ahead log system, and use metadata storage for important info. To ensure fault tolerance, use a leader-follower approach with a coordination service and acknowledgment for write success assessment. Follow a structured approach and incorporate multiple producers and consumers for different topics to design an effective message queue.