Design a Key-Value Store like Redis or DynamoDB

Functional Requirements:

• Store and retrieve values by key (get, put operations).
• Update the value for an existing key.
• Delete a key-value pair.
• Support basic atomicity for single-key operations (no partial writes).

Non-Functional Requirements:

• Scalability: Should handle increasing data and request volume by adding more nodes.
• Durability: Data should not be lost in case of node failures.
• Availability: System should be able to serve requests even if some nodes are down.
• Consistency: For this design, prioritize eventual consistency (like DynamoDB), but allow for configuration of stronger consistency if needed.
• Low latency: Reads and writes should be fast (ideally under a few milliseconds for in-memory data).
• Fault tolerance: System should continue to operate in the presence of node or network failures.