Implement Circuit Breakers

Ticket ID: Implement Circuit Breakers
Priority: High
Estimated Effort: Medium (2 weeks)
Category: Architecture Improvements
Description:
Implement circuit breaker pattern using Resilience4j to improve application resilience against external service failures.

Tasks:

Add Resilience4j dependency to pom.xml.

Implement circuit breaker in BalanceServiceImpl.java for external service calls (e.g., getBalance method).

Create fallback method (getBalanceFallback) to handle failures gracefully.

Configure circuit breaker properties (e.g., failure rate threshold, wait duration).

Test circuit breaker behavior under simulated service failures.

Acceptance Criteria:

Resilience4j dependency is added to pom.xml.
BalanceServiceImpl.java includes @CircuitBreaker annotation with fallback method.
Fallback method returns a BalanceResponse with SERVICE_UNAVAILABLE status and appropriate message.
Circuit breaker triggers correctly during simulated failures (verified via logs).
Application remains stable during external service outages.

Dependencies:

Testing environment to simulate service failures.
Logging setup to monitor circuit breaker events.