Capstone – Article 14: Logging, Monitoring & Actuator (Expense Tracker)

1. Introduction

A production system is not complete if you cannot observe it.

Logging and monitoring help you:

• Debug issues quickly
• Understand system behavior
• Detect failures early

In this article, we will make the Expense Tracker observable and production-ready.

---

2. Logging Strategy

Spring Boot uses:

• SLF4J (API)
• Logback (implementation)

Good logging answers:

• What happened?
• When did it happen?
• Why did it fail?

---

3. Adding Loggers in Code

Example in service layer:

private static final Logger log =
        LoggerFactory.getLogger(ExpenseService.class);

public ExpenseResponse createExpense(ExpenseRequest request) {
    log.info("Creating expense for logged-in user");
    ExpenseResponse response = saveExpense(request);
    log.debug("Expense created with id {}", response.getId());
    return response;
}

Guidelines: ✔ Use INFO for business flow
✔ DEBUG for details
✔ ERROR for failures

---

4. Configuring Log Levels

In application.properties:

logging.level.root=INFO
logging.level.com.example.expensetracker=DEBUG

This:

• Keeps logs readable
• Enables debugging for your code only

---

5. Log Format

logging.pattern.console=%d{yyyy-MM-dd HH:mm:ss} %-5level %logger - %msg%n

Readable logs save time during incidents.

---

6. Introducing Spring Boot Actuator

Actuator provides:

• Health checks
• Metrics
• App info
• Environment visibility

Add dependency (if not already added):

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

---

7. Important Actuator Endpoints

Endpoint	Purpose
/actuator/health	App health
/actuator/info	App info
/actuator/metrics	Metrics
/actuator/env	Environment

---

8. Exposing Actuator Endpoints

management.endpoints.web.exposure.include=health,info,metrics

Test:

GET /actuator/health

---

9. Custom Health Indicator

@Component
public class DatabaseHealthIndicator implements HealthIndicator {

    @Override
    public Health health() {
        boolean dbUp = true; // simulate DB check

        if (dbUp) {
            return Health.up().build();
        }
        return Health.down().withDetail("Database", "Not reachable").build();
    }
}

Custom health checks are used heavily in production.

---

10. Securing Actuator Endpoints

Never expose sensitive endpoints publicly.

management.endpoints.web.exposure.include=health

Secure others using Spring Security.

---

11. Observing Metrics

Example metric:

/actuator/metrics/jvm.memory.used

Useful for:

• Memory leaks
• Performance tuning

---

12. Common Logging & Monitoring Mistakes

❌ Logging sensitive data
❌ Excessive DEBUG logs in prod
❌ No health checks
❌ Ignoring logs until failure

---

13. Git Commit (Important)

git add .
git commit -m "Add logging and actuator monitoring"

---

14. What You Should Have Now

At this point:

• Logs are structured
• Health endpoints work
• Metrics are available
• App is observable

---

15. What’s Next?

➡ Capstone – Article 15: Dockerization & Deployment

• Dockerfile
• Containerization
• Cloud deployment

Type Next when you’re ready 🚀