Design a distributed system for real-time data processing with fault tolerance and scalability. Specifically, develop a system that can handle large-scale sensor data for a smart city infrastructure. The system must meet the following requirements:

1. Real-time Data Processing: The system should process sensor data from thousands of sensors with minimal latency.
2. Fault Tolerance: It should be resilient to node failures and data loss.
3. Scalability: The system must be able to scale horizontally as the number of sensors increases.
4. Data Consistency: Ensure data consistency across distributed nodes.
5. Cost Efficiency: Optimize for cost while maintaining performance.