Health Checks & Resilience Patterns
Design robust health checks, implement circuit breakers, and apply other resilience patterns for fault-tolerant systems.
Health Checks & Resilience Patterns is a free Spring Boot 4 Complete Guide lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Boot 4 Complete Guide learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Introduction to Health Checks
In production, applications need to be robust. Health checks are automated ways to verify if an application or service is running correctly and ready to receive traffic.
- They tell orchestrators (like Kubernetes) if your app is alive.
- They prevent traffic from being sent to unhealthy instances.
- They help in automatic recovery and scaling decisions.
Spring Boot Actuator Health
Spring Boot Actuator provides a built-in /actuator/health endpoint. By default, it aggregates health information from various components like databases, disk space, and more.
When accessed, it returns a status, typically UP or DOWN, along with details about included components.
Accessing Health Endpoint
To see the health status, you just need to enable Actuator and access the endpoint. Here's how you might configure it in application.properties:
management.endpoints.web.exposure.include=health
management.endpoint.health.show-details=alwaysCustom Health Indicators
Sometimes, the default health checks aren't enough. You might have an external API, a custom cache, or a specific business logic that needs monitoring.
You can create custom health indicators by implementing the HealthIndicator interface to add your own checks to the /actuator/health endpoint.
Implementing a Custom Indicator
Let's create a simple custom health indicator for a hypothetical external service. If the service is 'available', it reports UP; otherwise, DOWN.
import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;
@Component
public class ExternalServiceHealthIndicator implements HealthIndicator {
private final String SERVICE_NAME = "MyExternalService";
@Override
public Health health() {
if (isExternalServiceUp()) {
return Health.up().withDetail(SERVICE_NAME, "Available").build();
} else {
return Health.down().withDetail(SERVICE_NAME, "Not Available").build();
}
}
private boolean isExternalServiceUp() {
// Simulate checking external service status
// In a real app, this would involve network calls, DB queries, etc.
return Math.random() > 0.3; // 70% chance of being up
}
public static void main(String[] args) {
ExternalServiceHealthIndicator indicator = new ExternalServiceHealthIndicator();
System.out.println("Service Health: " + indicator.health().getStatus());
}
}Liveness vs. Readiness Probes
When deploying to container orchestrators like Kubernetes, two types of probes are crucial:
- Liveness Probe: Determines if an application instance is running. If it fails, Kubernetes restarts the container.
- Readiness Probe: Determines if an application instance is ready to serve traffic. If it fails, Kubernetes stops sending traffic to it.
Spring Boot 2.3+ introduced distinct health groups for these, often mapped to /actuator/health/liveness and /actuator/health/readiness.
Introduction to Resilience
Even with health checks, external dependencies can fail, causing your application to crash or slow down. Resilience patterns help your application gracefully handle failures and continue operating under adverse conditions.
- They improve fault tolerance and stability.
- They prevent cascading failures across services.
- They ensure a better user experience even when parts of the system are struggling.
The Circuit Breaker Pattern
The Circuit Breaker pattern prevents an application from repeatedly trying to execute an operation that is likely to fail. It's like an electrical circuit breaker: if too much current flows, it trips to prevent damage.
- CLOSED: Requests pass through. If failures exceed a threshold, it trips to OPEN.
- OPEN: Requests immediately fail (fast-fail). After a timeout, it transitions to HALF_OPEN.
- HALF_OPEN: A limited number of test requests are allowed. If they succeed, it closes; otherwise, it opens again.
Circuit Breaker with Resilience4j
Resilience4j is a popular library for implementing resilience patterns. Here's a simplified example of a circuit breaker protecting a slow method call.
import io.github.resilience4j.circuitbreaker.CircuitBreaker;
import io.github.resilience4j.circuitbreaker.CircuitBreakerConfig;
import io.github.resilience4j.circuitbreaker.CircuitBreakerRegistry;
import java.time.Duration;
public class CircuitBreakerDemo {
private final CircuitBreaker circuitBreaker;
public CircuitBreakerDemo() {
CircuitBreakerConfig circuitBreakerConfig = CircuitBreakerConfig.custom()
.failureRateThreshold(50) // 50% failure rate to open
.waitDurationInOpenState(Duration.ofSeconds(5)) // 5s before HALF_OPEN
.ringBufferSizeInHalfOpenState(2) // 2 calls in HALF_OPEN
.ringBufferSizeInClosedState(5) // 5 calls in CLOSED for failure rate calc
.build();
CircuitBreakerRegistry circuitBreakerRegistry =
CircuitBreakerRegistry.of(circuitBreakerConfig);
circuitBreaker = circuitBreakerRegistry.circuitBreaker("myService");
}
public String callExternalService() {
return circuitBreaker.executeSupplier(() -> {
if (Math.random() < 0.6) { // Simulate 60% failure rate
throw new RuntimeException("Service failed!");
}
return "Service Data";
});
}
public static void main(String[] args) {
CircuitBreakerDemo demo = new CircuitBreakerDemo();
for (int i = 0; i < 15; i++) {
try {
System.out.println(i + ": " + demo.callExternalService());
} catch (Exception e) {
System.err.println(i + ": Error - " + e.getMessage() +
" | CB State: " + demo.circuitBreaker.getState());
try { Thread.sleep(500); } catch (InterruptedException ie) {}
}
}
}
}Fallback Methods
When a circuit breaker is open or a service call fails, you don't always want to just throw an error. A fallback method provides an alternative response or action when the primary operation fails.
This allows your application to degrade gracefully, perhaps by returning cached data, a default response, or an empty list, instead of crashing or showing a full error page.
Quick Check on Resilience
Which of the following are benefits of implementing resilience patterns like the Circuit Breaker?
Recap: Health & Resilience
We've explored how health checks, particularly with Spring Boot Actuator and custom indicators, help monitor application status and readiness for traffic.
We also learned about resilience patterns, focusing on the Circuit Breaker, to prevent cascading failures and ensure graceful degradation when external services or components fail. Implementing these patterns is key for building robust, production-ready microservices.
Frequently asked questions
Is the “Health Checks & Resilience Patterns” lesson free?
Yes — the full text of “Health Checks & Resilience Patterns” is free to read here on the web, and the Spring Boot 4 Complete Guide course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Boot 4 Complete Guide course, upgrade to CoddyKit PRO.
What will I learn in “Health Checks & Resilience Patterns”?
Design robust health checks, implement circuit breakers, and apply other resilience patterns for fault-tolerant systems. You practise Spring Boot 4 Complete Guide with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Spring Boot 4 Complete Guide?
No prior experience is required. Spring Boot 4 Complete Guide on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Health Checks & Resilience Patterns” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Spring Boot 4 Complete Guide lesson?
Yes. Every Spring Boot 4 Complete Guide lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Kubernetes Orchestration Basics
- Distributed Tracing with Sleuth & Zipkin
- Health Checks & Resilience Patterns
- Metrics and Dashboards with Micrometer and Prometheus