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Spring Boot Actuators

3 min read

Definitions

Actuator: Spring Boot feature exposing operational management endpoints via HTTP or JMX. Provides runtime visibility into application metrics, health, environment, and configuration.

Endpoint: Specific actuator functionality exposed as HTTP endpoint (e.g., /actuator/health, /actuator/metrics). Configurable for inclusion/exclusion and web/JMX exposure.

Health Indicator: Component reporting health status of application and dependent systems (database, cache, message broker). Returns UP, DOWN, or OUT_OF_SERVICE status.

Metrics: Application measurements (counters, gauges, timers, histograms) tracked for performance monitoring and analysis. Integrated with Micrometer for vendor-neutral metrics.

Custom Actuator: User-defined endpoint or health indicator extending Spring Boot’s monitoring capabilities for application-specific metrics and checks.

Q&A

What is the purpose of Spring Boot Actuator?

Actuator provides production-ready monitoring and management capabilities. Exposes application internals (health, metrics, logs, environment) via REST endpoints or JMX, enabling operational teams to monitor performance, diagnose issues, and manage application runtime behavior without code changes.

How do you enable Actuator in a Spring Boot application?

Add spring-boot-starter-actuator dependency to POM/Gradle. Actuator automatically configures upon startup, exposing endpoints based on environment (web/JMX). Configure exposure via management.endpoints.web.exposure.include property (whitelist endpoints to expose). By default, only /actuator/health and /actuator/info are exposed.

What are some important Actuator endpoints?

Common endpoints include: /actuator/health (application health status), /actuator/metrics (list available metrics), /actuator/env (environment properties), /actuator/loggers (logger configuration), /actuator/threaddump (thread information), /actuator/httptrace (HTTP request/response history), /actuator/configprops (configuration properties).

How do you customize health indicators?

Implement HealthIndicator interface with health() method returning Health.up() or Health.down() with details. Component name derives from class name (e.g., DatabaseHealthIndicator → /actuator/health/database). Spring automatically detects and includes custom indicators.

Can you disable specific Actuator endpoints?

Yes, configure management.endpoints.web.exposure.exclude property to hide specific endpoints. Example: management.endpoints.web.exposure.exclude=env,configprops. Alternatively, use management.endpoint.*.enabled=false to disable individual endpoints. Security can further restrict access.

How do you add custom metrics to your application?

Use MeterRegistry (from Micrometer) to create counters, timers, gauges. Inject MeterRegistry bean, then call methods like registry.counter("myapp.counter").increment(). Metrics automatically exported to monitoring systems (Prometheus, Grafana, etc.). Custom metrics appear in /actuator/metrics endpoint.

Code Examples

Example - Maven Dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

Example - Enable Actuator Endpoints (application.yml):

management:
  endpoints:
    web:
      exposure:
        include: health,metrics,env,loggers
  endpoint:
    health:
      show-details: when-authorized

Example - Custom Health Indicator:

@Component
public class DatabaseHealthIndicator implements HealthIndicator {
    @Override
    public Health health() {
        try {
            // Check database connectivity
            boolean isHealthy = checkDatabase();
            if (isHealthy) {
                return Health.up().withDetail("database", "Connected").build();
            } else {
                return Health.down().withDetail("database", "Connection failed").build();
            }
        } catch (Exception e) {
            return Health.down().withException(e).build();
        }
    }
}

Example - Custom Metrics:

@RestController
public class MyController {
    private final MeterRegistry meterRegistry;
    
    public MyController(MeterRegistry meterRegistry) {
        this.meterRegistry = meterRegistry;
    }
    
    @GetMapping("/api/data")
    public ResponseEntity<?> getData() {
        meterRegistry.counter("myapp.api.calls").increment();
        meterRegistry.timer("myapp.api.duration").record(() -> {
            // Business logic
        });
        return ResponseEntity.ok("data");
    }
}

Key Points

  • Security: Actuator endpoints are operational; restrict access via Spring Security in production.
  • Performance: Enabling all endpoints may expose sensitive information; whitelist only necessary endpoints.
  • Health Details: show-details property controls what health information is exposed (never, when-authorized, always).
  • Metrics Integration: Micrometer supports multiple backends; configure via management.metrics.export.* properties.
  • Custom Endpoints: Implement @Endpoint annotation for custom actuator endpoints beyond predefined ones.

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