The Circuit Breaker pattern is a resilience design pattern that prevents cascading failures in distributed systems. It works like an electrical circuit breaker - when failures reach a threshold, it "opens" and stops calling the failing service, allowing it time to recover.
Problems it solves:

• Prevents resource exhaustion from repeated calls to failing services
• Stops cascading failures across microservices
• Provides fail-fast behavior instead of hanging requests
• Allows graceful degradation of functionality
  Circuit Breaker states:
• Closed: Normal operation, requests pass through to the service
• Open: Failure threshold exceeded, requests fail immediately without calling the service
• Half-Open: Testing mode to check if the downstream service has recovered

Closed State:

• Default state where requests flow normally to the downstream service
• Monitors failure rate and response times
• When failure threshold is exceeded, transitions to Open state
  Open State:
• All requests fail immediately without calling the downstream service
• Returns cached data, default values, or error responses
• Has a timeout period before transitioning to Half-Open
• Prevents resource waste and allows downstream service to recover
  Half-Open State:
• Allows a limited number of test requests to check service health
• If test requests succeed, transitions back to Closed
• If test requests fail, returns to Open state
• Acts as a "probe" to determine if the service has recovered

The Bulkhead pattern isolates different parts of a system into separate resource pools to prevent failure in one area from affecting others. It's named after ship bulkheads that prevent water from flooding the entire vessel.
Key differences from Circuit Breaker:
Bulkhead Pattern:

• Isolation: Separates resources (threads, connections, memory)
• Prevention: Stops resource exhaustion before it happens
• Scope: Protects internal system resources
• Strategy: Resource partitioning
  Circuit Breaker Pattern:
• Protection: Stops calls to failing external services
• Detection: Reacts after failures are detected
• Scope: Protects against external dependency failures
• Strategy: Request blocking
  Example scenario:

// Bulkhead: Separate thread pools for different operations
ThreadPoolExecutor paymentPool = new ThreadPoolExecutor(5, 10, ...);
ThreadPoolExecutor notificationPool = new ThreadPoolExecutor(3, 6, ...);
// Circuit Breaker: Protect calls to external payment service
CircuitBreaker paymentServiceBreaker = new CircuitBreaker();