The primary objectives for the distributed unique ID generator include:

• Uniqueness: Ensure that each generated ID is unique globally across distributed nodes.
• High Throughput: Support thousands of requests per second without significant latency.
• Minimal Synchronization Overhead: Reduce the need for coordination or locking mechanisms among nodes to prevent bottlenecks.
• Fault Tolerance: Ensure the system can continue operating efficiently even if some nodes fail.

Additionally, we should take scalability into account to accommodate growth, as well as a reasonable persistence strategy to keep track of state if necessary.

Estimating the capacity of the ID generator depends on the number of unique IDs required and the expected growth over time. Here are some considerations:

• ID Format: Using a numeric format will generally yield a higher throughput than string-based alternatives.
• Scaling Factor: The system should be designed for at least 10x the projected load to handle unpredictable spikes.
• Node Count: With horizontal scalability, deploying multiple instances of the generator will allow increased throughput, requiring a balance between ID generation speed and resource consumption.

Lastly, periodic performance testing will ensure that the system meets the throughput needs as well as the overall system requirements.

For interoperability and ease of use, a straightforward REST API can be designed. API endpoints may include:

• GET /generateId: Generates and returns a new unique ID.
• GET /health: Checks the health status of the ID generation service.

Returning a simple JSON response for the generated ID as well as any errors will help standardize communications with clients. Authentication measures should also be considered to secure the endpoint.

While the primary function of the system does not hinge on traditional storage solutions for IDs, maintaining a persistent layer could enhance fault tolerance:

• Database Choice: A NoSQL database (type) like Cassandra or DynamoDB can provide high write availability, suitable for unique ID storage.
• Schema: Even though IDs may not be stored persistently, logging generated IDs can be useful for audit and monitoring purposes.

This allows us to periodically assess performance and identify any anomalies.

The high-level architecture features several components working together for scalability and performance:

• Client: Sends requests for unique IDs.
• Load Balancer: Distributes incoming requests evenly across multiple ID generating services.
• Id Generation Services: Stateless services responsible for generating unique IDs.
• Database: Stores logs of generated IDs (if necessary).

Each component should be designed to scale independently, with the load balancer facilitating access to multiple ID generating services and enabling redundancy.

Upon receiving a request for a unique ID, the flow can be outlined as follows:

• The client sends a request to the load balancer.
• The load balancer forwards the request to an available ID generation service.
• The ID generation service produces a unique ID locally.
• The service returns the ID to the load balancer, which then sends it back to the client.

This flow allows for quick and effective processing of ID requests while maintaining service health tracking.

The main components of the system can be detailed as follows:

• Load Balancer: Spreads requests to multiple ID generator nodes.
• ID Generator Node: Each node generates unique IDs using a combination of time-stamping and node identification.
• Metrics Collector: Gathers performance data for monitoring.

All components should communicate over well-defined interfaces, allowing modular upgrades and troubleshooting.

Every architectural decision has trade-offs that need to be considered:

• Consistency vs. Availability: Prioritizing availability might lead to temporary ID collisions, depending on the generation approach.
• ID Generation Algorithm: Using a time-based UUID eliminates collisions but may introduce slight delays.

Balancing these trade-offs is pivotal in aligning with system goals while ensuring high performance.

Several failure scenarios should be accounted for, including:

• Node Failure: If an ID generation node fails, the load balancer should reroute requests to another operational node.
• Network Issues: Implement retries or circuit breakers to handle network latency or errors.
• Database Outage: If logging fails, ensure that ID generation continues to operate, relying on in-memory states.

These scenarios should be tested regularly to ensure robustness.

Looking ahead, we can consider the following enhancements:

• Dynamic Scaling: Implement mechanisms for auto-scaling services based on load.
• Improved ID Retrievability: Facilitating querying of previously generated IDs could enhance system auditability.

Continuous improvements will enable the system to adapt to changing demands efficiently.