Why monitoring matters in Spring Boot - See It in Action

Why monitoring matters

📖 Scenario: You are running a small Spring Boot web application that serves users. To keep your app healthy and responsive, you want to monitor its status and key metrics like uptime and request count.

🎯 Goal: Build a simple Spring Boot app with a health check endpoint and a counter for requests. Then add monitoring logic to track and display these metrics.

📋 What You'll Learn

Create a Spring Boot application class

Add a REST controller with a health check endpoint

Add a request counter variable

Increment the counter on each request

Print the current health status and request count

💡 Why This Matters

🌍 Real World

Monitoring helps keep applications running smoothly by alerting you to problems early. This simple app shows how to track basic health and usage.

💼 Career

DevOps engineers and backend developers often build and maintain monitoring endpoints to ensure system reliability and performance.

1

Create Spring Boot application class

Create a Spring Boot application class called MonitoringApp with the @SpringBootApplication annotation and a main method that runs the app using SpringApplication.run(MonitoringApp.class, args).

Spring Boot

// Your code here

Hint

Use @SpringBootApplication on the class and write a main method that calls SpringApplication.run.

2

Add REST controller with health check

Add a REST controller class called HealthController with the @RestController annotation. Inside it, create a method healthCheck mapped to /health using @GetMapping that returns the string "UP".

Spring Boot

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;

// Your code here

Hint

Use @RestController on the class and @GetMapping("/health") on the method that returns "UP".

3

Add request counter and increment logic

Inside the HealthController class, add a private integer variable called requestCount initialized to 0. Modify the healthCheck method to increment requestCount by 1 each time it is called.

Spring Boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;

@SpringBootApplication
public class MonitoringApp {
    public static void main(String[] args) {
        SpringApplication.run(MonitoringApp.class, args);
    }
}

@RestController
class HealthController {
    private int requestCount = 0;

    @GetMapping("/health")
    public String healthCheck() {
        // Your code here
    }
}

Hint

Declare private int requestCount = 0; and add requestCount++; inside the healthCheck method.

4

Print health status and request count

Modify the healthCheck method to return a string showing both the health status and the current requestCount in this format: "Status: UP, Requests: X" where X is the value of requestCount. Use String.format to build the string.

Spring Boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;

@SpringBootApplication
public class MonitoringApp {
    public static void main(String[] args) {
        SpringApplication.run(MonitoringApp.class, args);
    }
}

@RestController
class HealthController {
    private int requestCount = 0;

    @GetMapping("/health")
    public String healthCheck() {
        requestCount++;
        // Your code here
    }
}

Hint

Use return String.format("Status: UP, Requests: %d", requestCount); to show the status and count.

Practice

1. Why is monitoring important in a Spring Boot application?

easy

A. It replaces the need for writing tests.

B. It automatically fixes all bugs without developer input.

C. It slows down the application to prevent overload.

D. It helps detect problems early and keeps the app running smoothly.

Solution

1. Step 1: Understand monitoring purpose

   Monitoring tracks app health and performance in real time.

2. Step 2: Identify benefits in Spring Boot context

   It helps find and fix issues quickly, ensuring smooth operation.

3. Final Answer:

   It helps detect problems early and keeps the app running smoothly. -> Option D

4. Quick Check:

   Monitoring = Early problem detection [OK]

Hint: Monitoring = early problem detection and smooth running [OK]

Common Mistakes:

• Thinking monitoring fixes bugs automatically
• Believing monitoring slows the app down
• Confusing monitoring with testing

2. Which Spring Boot dependency is commonly used to add monitoring features?

easy

A. spring-boot-starter-web

B. spring-boot-starter-actuator

C. spring-boot-starter-data-jpa

D. spring-boot-starter-security

Solution

1. Step 1: Identify monitoring-related starter

   Spring Boot Actuator provides built-in monitoring endpoints.

2. Step 2: Match dependency to monitoring

   spring-boot-starter-actuator adds monitoring and health check features.

3. Final Answer:

   spring-boot-starter-actuator -> Option B

4. Quick Check:

   Actuator = monitoring starter [OK]

Hint: Actuator starter adds monitoring endpoints easily [OK]

Common Mistakes:

• Choosing web starter which is for web apps
• Confusing data-jpa with monitoring
• Selecting security starter unrelated to monitoring

3. Given this Spring Boot Actuator endpoint configuration:
management.endpoints.web.exposure.include=health,info
What will be the output when accessing /actuator/health?

medium

A. {"status":"DOWN"}

B. {"error":"Endpoint not found"}

C. {"status":"UP"}

D. {"info":"No data"}

Solution

1. Step 1: Check exposed endpoints

   Only 'health' and 'info' endpoints are exposed via web.

2. Step 2: Understand default health output

   By default, health endpoint returns {"status":"UP"} if app is running well.

3. Final Answer:

   {"status":"UP"} -> Option C

4. Quick Check:

   Health endpoint = {"status":"UP"} when healthy [OK]

Hint: Health endpoint shows status UP if app is healthy [OK]

Common Mistakes:

• Expecting error when endpoint is exposed
• Confusing info endpoint output with health
• Assuming status DOWN without failure

4. You added Spring Boot Actuator but /actuator/health returns 404 error. What is the likely cause?

medium

A. The endpoint is disabled or not exposed in configuration.

B. The URL path is incorrect; it should be /health.

C. The application is not running.

D. Actuator dependency is missing in the project.

Solution

1. Step 1: Confirm Actuator dependency presence

   If dependency was missing, app wouldn't compile or actuator endpoints wouldn't exist.

2. Step 2: Check endpoint exposure settings

   By default, some actuator endpoints are disabled or not exposed over web, causing 404.

3. Final Answer:

   The endpoint is disabled or not exposed in configuration. -> Option A

4. Quick Check:

   Disabled endpoint = 404 error [OK]

Hint: Check actuator endpoint exposure settings if 404 occurs [OK]

Common Mistakes:

• Assuming missing dependency without checking config
• Thinking app not running causes 404 instead of connection error
• Using wrong URL path for actuator endpoints

5. You want to monitor custom metrics in your Spring Boot app. Which approach best fits this need?

hard

A. Add custom metrics using Micrometer and expose them via Actuator endpoints.

B. Write logs manually and parse them later for metrics.

C. Use only the default health endpoint without changes.

D. Disable Actuator and rely on external monitoring tools only.

Solution

1. Step 1: Understand custom metrics requirement

   Custom metrics need to be collected and exposed in a structured way.

2. Step 2: Identify Spring Boot recommended method

   Micrometer integrates with Actuator to add and expose custom metrics easily.

3. Final Answer:

   Add custom metrics using Micrometer and expose them via Actuator endpoints. -> Option A

4. Quick Check:

   Micrometer + Actuator = custom metrics [OK]

Hint: Use Micrometer with Actuator for custom metrics [OK]

Common Mistakes:

• Relying only on logs for metrics
• Using default health endpoint for custom metrics
• Disabling Actuator loses monitoring benefits