Working and Different States in Circuit Breaker Pattern
The Circuit Breaker pattern typically operates in three main states: Closed, Open, and Half-Open. Each state represents a different phase in the management of interactions between services. Here’s an explanation of each state:
1. Closed State
- In the Closed state, the circuit breaker operates normally, allowing requests to flow through between services.
- During this phase, the circuit breaker monitors the health of the downstream service by collecting and analyzing metrics such as response times, error rates, or timeouts.
- If the monitored metrics remain within acceptable thresholds, indicating that the downstream service is healthy, the circuit breaker stays in the Closed state and continues to forward requests.
2. Open State
- When the monitored metrics breach predetermined thresholds, signaling potential issues with the downstream service, the circuit breaker transitions to the Open state.
- In the Open state, the circuit breaker immediately stops forwarding requests to the failing service, effectively isolating it.
- Instead of allowing requests to reach the failing service and potentially exacerbate the issue, the circuit breaker provides a predefined fallback response or an error message to the caller.
- This helps prevent cascading failures and maintains system stability by ensuring that clients receive timely feedback, even when services encounter issues.
3. Half-Open State
- After a specified timeout period in the Open state, transitions to Half-Open state.
- Allows a limited number of trial requests to pass through to the downstream service.
- Monitors responses to determine service recovery.
- If trial requests succeed, indicating service recovery, transitions back to Closed state.
- If trial requests fail, service issues persist.
- May transition back to Open state or remain in Half-Open state for further evaluation.
In the above diagram:
- Closed State to Open State:
- Transition Trigger: Request failed with threshold limit.
- Explanation: When the monitored metrics breach the predefined thresholds while the Circuit Breaker is in the Closed state, indicating potential issues with the downstream service, it transitions to the Open state. This means that the Circuit Breaker stops forwarding requests to the failing service(that is experiencing issues or failures)and provides fallback responses to callers.
- Half-Open State to Closed State:
- Transition Trigger: Request successful with threshold value.
- Explanation: After a specified timeout period in the Open state, the Circuit Breaker transitions to the Half-Open state. In the Half-Open state, a limited number of trial requests are allowed to pass through to the downstream service. If these trial requests are successful and the service appears to have recovered, the Circuit Breaker transitions back to the Closed state, allowing normal traffic to resume.
- Half-Open State to Open State:
- Transition Trigger: Request failed.
- Explanation: While in the Half-Open state, if the trial requests to the downstream service fail, indicating that the service is still experiencing issues, the Circuit Breaker transitions back to the Open state. This means that requests will again be blocked, and fallback responses will be provided until the service’s health improves.
- Open State to Half-Open State:
- Transition Trigger: Counter reset timeout.
- Explanation: After a specified timeout period in the Open state, the Circuit Breaker transitions to the Half-Open state. This timeout period allows the Circuit Breaker to periodically reevaluate the health of the downstream service and determine if it has recovered.
What is Circuit Breaker Pattern in Microservices?
The Circuit Breaker pattern in microservices acts as a safeguard against service failures by monitoring interactions, setting thresholds, and temporarily halting/Stoping traffic to failing services. It helps prevent cascading failures and maintains system stability, ensuring reliable performance in distributed architectures.
Important Topics for Circuit Breaker Pattern in Microservices
- What is a Circuit Breaker Pattern?
- Characteristics of Circuit Breaker Pattern
- Importance of Circuit Breaker Pattern
- Working and Different States in Circuit Breaker Pattern
- Steps to Implement Circuit Breaker Pattern
- Use Cases of Circuit Breaker Pattern
- Benefits of Circuit Breaker Pattern
- Challenges of Circuit Breaker Pattern in Microservices
- When to use Circuit Breaker Pattern