Spring Boot Actuator

@RestController
public class HealthEndpoint {

    @Autowired
    private DataSource dataSource;

    @GetMapping("/health")
    public Map<String, Object> health() {
        Map<String, Object> health = new HashMap<>();

        // => Manual database check
        try (Connection conn = dataSource.getConnection()) {
            health.put("database", "UP");
        } catch (SQLException e) {
            health.put("database", "DOWN");
            health.put("status", "DOWN");
            return health;
        }

        // => Manual disk space check
        File root = new File("/");
        long freeSpace = root.getFreeSpace();
        health.put("diskSpace", freeSpace > 10_000_000 ? "UP" : "DOWN");

        health.put("status", "UP");
        return health;
    }
}

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

management:
  endpoints:
    web:
      exposure:
        include: health,info,metrics,prometheus
        # => Expose specific endpoints (security-conscious)
        # => Production: selective exposure (not "*")
      base-path: /actuator # => Base path for all endpoints

  endpoint:
    health:
      show-details: when-authorized
      # => Show details only for authorized users
      # => Production: hide internal details from public
      probes:
        enabled: true # => Kubernetes liveness/readiness probes

  health:
    livenessState:
      enabled: true
    readinessState:
      enabled: true

# => Health check (Kubernetes liveness probe)
curl http://localhost:8080/actuator/health
# => {"status":"UP"}

# => Detailed health (authenticated)
curl -H "Authorization: Bearer $TOKEN" http://localhost:8080/actuator/health
# => {
#   "status": "UP",
#   "components": {
#     "db": { "status": "UP", "details": { "database": "PostgreSQL", "validationQuery": "isValid()" } },
#     "diskSpace": { "status": "UP", "details": { "total": 500GB, "free": 200GB } }
#   }
# }

# => Metrics
curl http://localhost:8080/actuator/metrics
# => {"names": ["jvm.memory.used", "http.server.requests", ...]}

curl http://localhost:8080/actuator/metrics/jvm.memory.used
# => {"name": "jvm.memory.used", "measurements": [{"statistic": "VALUE", "value": 512MB}]}

@Component
public class ZakatServiceHealthIndicator implements HealthIndicator {

    @Autowired
    private ZakatCalculationService calculationService;

    @Override
    public Health health() {
        try {
            // => Custom health check: verify service works
            BigDecimal testResult = calculationService.calculateNisab();

            if (testResult.compareTo(BigDecimal.ZERO) > 0) {
                return Health.up()
                    .withDetail("nisab", testResult)
                    .withDetail("service", "operational")
                    .build();  // => Status: UP
            } else {
                return Health.down()
                    .withDetail("error", "Invalid nisab calculation")
                    .build();  // => Status: DOWN
            }
        } catch (Exception e) {
            return Health.down(e)
                .withDetail("error", e.getMessage())
                .build();  // => Status: DOWN with exception details
        }
    }
}

# => Kubernetes deployment with Actuator health probes
apiVersion: apps/v1
kind: Deployment
metadata:
  name: zakat-api
spec:
  template:
    spec:
      containers:
        - name: zakat-api
          image: zakat-api:1.0.0
          ports:
            - containerPort: 8080

          # => Liveness probe: restart if fails
          livenessProbe:
            httpGet:
              path: /actuator/health/liveness
              port: 8080
            initialDelaySeconds: 30
            periodSeconds: 10
            timeoutSeconds: 5
            failureThreshold: 3

          # => Readiness probe: remove from service if fails
          readinessProbe:
            httpGet:
              path: /actuator/health/readiness
              port: 8080
            initialDelaySeconds: 10
            periodSeconds: 5
            timeoutSeconds: 3
            failureThreshold: 3

# => application.yml
management:
  metrics:
    export:
      prometheus:
        enabled: true # => Enable Prometheus format
  endpoints:
    web:
      exposure:
        include: prometheus # => Expose /actuator/prometheus

# => prometheus.yml
scrape_configs:
  - job_name: "spring-boot-zakat-api"
    metrics_path: "/actuator/prometheus"
    static_configs:
      - targets: ["zakat-api:8080"]