Spring Boot Actuator

 Spring Boot Actuator is a powerful module that provides production-ready features to help you monitor and manage your Spring Boot application.

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📌 What is Actuator?

Spring Boot Actuator exposes several built-in endpoints that give insights into your application:

• Health

• Metrics

• Environment

• Beans

• Thread dumps

• HTTP trace

• Custom endpoints

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✅ Step-by-Step Setup

🧱 1. Add Dependency

Maven:

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

Gradle:

groovy
implementation 'org.springframework.boot:spring-boot-starter-actuator'

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⚙️ 2. Configuration (application.yml or .properties)

application.yml (Recommended)

yaml
management:
  endpoints:
    web:
      exposure:
        include: "*"        # Expose all endpoints
  endpoint:
    health:
      show-details: always # Show health details (disk, db, etc.)
  info:
    env:
      enabled: true

If using .properties

properties
management.endpoints.web.exposure.include=*
management.endpoint.health.show-details=always

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🚀 3. Access Endpoints

Once Actuator is enabled and running (on default port 8080), you can hit these endpoints:

Endpoint	Description	URL Example
/actuator	List all enabled endpoints	http://localhost:8080/actuator
/actuator/health	Application health status	http://localhost:8080/actuator/health
/actuator/metrics	Performance metrics (memory, etc.)	http://localhost:8080/actuator/metrics
/actuator/beans	All Spring beans	http://localhost:8080/actuator/beans
/actuator/env	All environment variables	http://localhost:8080/actuator/env
/actuator/info	Project info (from info.*)	http://localhost:8080/actuator/info
/actuator/loggers	Log levels (change at runtime)	http://localhost:8080/actuator/loggers

🔐 4. Security with Spring Security (Optional)

By default, Actuator endpoints are secured if Spring Security is on the classpath.

To allow all endpoints without auth (not for production):

yaml
management:
  endpoints:
    web:
      exposure:
        include: "*"

spring:
  security:
    user:
      name: admin
      password: admin123

Login using admin/admin123 in browser when accessing endpoints.

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➕ Custom Info Endpoint

Add this to application.yml:

yaml
info:
  app:
    name: MyApp
    description: Custom Spring Boot app
    version: 1.0.0

Then check: http://localhost:8080/actuator/info

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➕ Custom Health Indicator

java
import org.springframework.boot.actuate.health.*;
import org.springframework.stereotype.Component;

@Component
public class CustomHealthIndicator implements HealthIndicator {
    @Override
    public Health health() {
        boolean appIsUp = true; // your custom logic
        if (appIsUp) {
            return Health.up().withDetail("custom", "Everything is OK!").build();
        }
        return Health.down().withDetail("custom", "Something is wrong").build();
    }
}

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🛠 Expose Actuator on a Different Port (Optional)

yaml
management:
  server:
    port: 9090

Now actuator is accessible at http://localhost:9090/actuator.

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📦 Use Cases

Use Case	Benefit
Kubernetes liveness/readiness	Check app status automatically
Prometheus/Grafana	Integrate metrics and monitoring
Debugging	View beans, thread dumps, env vars
DevOps Friendly	Health, metrics, restart, shutdown

📌 Summary

Feature	Default Status	Configurable
/actuator/health	✅ Enabled	Yes
/actuator/info	✅ Enabled	Yes
Others like /metrics, /beans	❌ Disabled by default	✅ Enable via config

✅ 2. Expose Custom Metrics using Micrometer

📌 Custom Metric Example

java
import io.micrometer.core.instrument.Counter;
import io.micrometer.core.instrument.MeterRegistry;
import org.springframework.stereotype.Component;

@Component
public class OrderMetrics {

    private final Counter orderCounter;

    public OrderMetrics(MeterRegistry registry) {
        this.orderCounter = registry.counter("orders.created.count");
    }

    public void incrementOrderCount() {
        orderCounter.increment();
    }
}

Use orderMetrics.incrementOrderCount() inside your service when an order is created.

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✅ 3. Write a Custom Actuator Endpoint

📦 Step-by-Step Custom Endpoint

a. Add a dependency for custom actuator endpoint support (optional)

No extra dependency needed unless you're using older Spring Boot (<2.0)

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b. Custom Endpoint Code

import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
import org.springframework.stereotype.Component;

import java.util.Map;

@Component
@Endpoint(id = "customstatus")
public class CustomStatusEndpoint {

    @ReadOperation
    public Map<String, String> customHealth() {
        return Map.of("app-status", "running", "uptime", "5h 23m");
    }
}

This exposes: http://localhost:8080/actuator/customstatus

You must explicitly expose it:

yaml
management:
  endpoints:
    web:
      exposure:
        include: health, prometheus, customstatus

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✅ Bonus: Custom HealthIndicator

java
import org.springframework.boot.actuate.health.*;
import org.springframework.stereotype.Component;

@Component
public class CustomHealthIndicator implements HealthIndicator {

    @Override
    public Health health() {
        boolean appHealthy = true; // your logic
        if (appHealthy) {
            return Health.up().withDetail("custom-check", "All good").build();
        } else {
            return Health.down().withDetail("custom-check", "Something failed").build();
        }
    }
}

It becomes part of /actuator/health.