Monitoring Circuit Breakers in Spring Boot

Monitoring circuit breakers is essential for maintaining resilient and reliable applications. In Spring Boot, you can use tools such as Resilience4j metrics, Micrometer, Prometheus, and Grafana to gain insights into circuit breaker behavior and health.

Key Metrics to Track

• Failure rate: measures the percentage of failed calls over a time window;
• Slow calls: counts the number of calls that exceed a predefined response time threshold;
• State transitions: tracks when a circuit breaker moves between CLOSED, OPEN, and HALF_OPEN states.

Collecting Metrics with Resilience4j and Micrometer

Resilience4j provides built-in support for exposing circuit breaker metrics. When you use the Resilience4j Spring Boot starter, metrics are automatically available through Micrometer. You can access these metrics at the /actuator/metrics endpoint.

Example metric names:

• resilience4j.circuitbreaker.calls
• resilience4j.circuitbreaker.state
• resilience4j.circuitbreaker.slow.calls

Exporting Metrics to Prometheus

To export metrics for visualization, integrate Prometheus with your Spring Boot application:

1. Add the micrometer-registry-prometheus dependency to your project;
2. Enable the /actuator/prometheus endpoint in your application.properties:

   management.endpoints.web.exposure.include=prometheus
   

3. Configure Prometheus to scrape the /actuator/prometheus endpoint.

Visualizing Metrics with Grafana

Grafana lets you create dashboards and alerts based on Prometheus data. You can:

• Build panels to display the current state of each circuit breaker;
• Chart the failure rate and the number of slow calls over time;
• Set up alerts to notify you when the failure rate exceeds a safe threshold or when a circuit breaker enters the OPEN state.

Example: Setting Up a Dashboard

1. Connect Grafana to your Prometheus data source.
2. Create a new dashboard and add a graph panel.
3. Use a query like:

   resilience4j_circuitbreaker_calls{result="failure", name="yourCircuitBreakerName"}
   

   to visualize failure counts for a specific circuit breaker.
4. Add alert conditions, such as sending a notification if the failure rate remains above 50% for five minutes.

By monitoring these metrics, you can quickly detect issues, respond to outages, and ensure your application remains robust and responsive.