Health endpoint customization in Spring Boot

Introduction

The health endpoint shows if your app is working well. Customizing it helps you add extra checks or change what info it shows.

You want to check if your database is connected.

You need to see if an external service your app uses is up.

You want to hide some details from the health report for security.

You want to add a custom message or status to the health check.

Syntax

Spring Boot

import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;

@Component
public class CustomHealthIndicator implements HealthIndicator {
    @Override
    public Health health() {
        // Your custom health check logic
        boolean serviceUp = checkService();
        if (serviceUp) {
            return Health.up().withDetail("service", "Available").build();
        } else {
            return Health.down().withDetail("service", "Not Available").build();
        }
    }

    private boolean checkService() {
        // Check your service here
        return true;
    }
}

Implement HealthIndicator and override health() to add custom checks.

Use Health.up() or Health.down() to set status and add details with withDetail().

Examples

This example adds a database check to the health endpoint.

Spring Boot

import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;

@Component
public class DatabaseHealthIndicator implements HealthIndicator {
    @Override
    public Health health() {
        boolean dbUp = checkDatabase();
        if (dbUp) {
            return Health.up().withDetail("database", "Connected").build();
        } else {
            return Health.down().withDetail("database", "Disconnected").build();
        }
    }

    private boolean checkDatabase() {
        // Simulate DB check
        return true;
    }
}

This example adds a simple custom message to the health status.

Spring Boot

import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;

@Component
public class CustomMessageHealthIndicator implements HealthIndicator {
    @Override
    public Health health() {
        return Health.up().withDetail("message", "All systems go!").build();
    }
}

Sample Program

This Spring Boot app has a custom health indicator that adds a "service" detail to the health endpoint. It returns "up" status with a message if the service is running.

Spring Boot

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;

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

@Component
class CustomHealthIndicator implements HealthIndicator {
    @Override
    public Health health() {
        boolean serviceRunning = checkService();
        if (serviceRunning) {
            return Health.up().withDetail("service", "Running smoothly").build();
        } else {
            return Health.down().withDetail("service", "Service down").build();
        }
    }

    private boolean checkService() {
        // Simulate service check logic
        return true;
    }
}

Important Notes

Custom health indicators automatically add their info to the main health endpoint at /actuator/health.

You can combine multiple health indicators for a full health report.

Remember to enable actuator endpoints in your application.properties if needed.

Summary

Health endpoint shows app status and can be customized to add checks.

Create a class implementing HealthIndicator and override health().

Use Health.up() or Health.down() with details to customize output.

Practice

1. What is the main purpose of customizing the health endpoint in Spring Boot?

easy

A. To automatically restart the application on failure

B. To change the port number of the application

C. To add specific checks that show detailed app status

D. To disable all health checks

Solution

1. Step 1: Understand the health endpoint role

   The health endpoint shows the app's status and can be extended to include custom checks.

2. Step 2: Identify customization purpose

   Customizing allows adding specific checks to provide detailed status beyond default info.

3. Final Answer:

   To add specific checks that show detailed app status -> Option C

4. Quick Check:

   Health endpoint customization = detailed app status [OK]

Hint: Health endpoint customization means adding detailed status checks [OK]

Common Mistakes:

• Thinking it changes app port
• Assuming it disables health checks
• Believing it restarts app automatically

2. Which interface must you implement to create a custom health check in Spring Boot?

easy

A. HealthIndicator

B. HealthCheck

C. HealthService

D. HealthStatus

Solution

1. Step 1: Recall Spring Boot health customization

   Custom health checks require implementing a specific interface.

2. Step 2: Identify correct interface

   The interface to implement is HealthIndicator, which requires overriding health().

3. Final Answer:

   HealthIndicator -> Option A

4. Quick Check:

   Custom health check interface = HealthIndicator [OK]

Hint: Custom health checks need HealthIndicator interface [OK]

Common Mistakes:

• Using HealthCheck instead of HealthIndicator
• Confusing with HealthService or HealthStatus
• Not overriding health() method

3. Given this custom health indicator code, what will the health endpoint show?

public class MyHealth implements HealthIndicator {
  @Override
  public Health health() {
    return Health.up().withDetail("db", "reachable").build();
  }
}

medium

A. {"status":"UP","details":{"db":"reachable"}}

B. {"status":"DOWN","details":{"db":"reachable"}}

C. {"status":"UP"}

D. {"status":"DOWN"}

Solution

1. Step 1: Analyze health() method return

   The method returns Health.up() with a detail key "db" set to "reachable".

2. Step 2: Understand output format

   The health endpoint shows status "UP" and includes the details map with "db":"reachable".

3. Final Answer:

   {"status":"UP","details":{"db":"reachable"}} -> Option A

4. Quick Check:

   Health.up() with details = status UP plus details [OK]

Hint: Health.up() withDetail adds details and sets status UP [OK]

Common Mistakes:

• Confusing UP with DOWN status
• Ignoring details in output
• Assuming default status without details

4. Identify the error in this custom health indicator code:

public class CustomHealth implements HealthIndicator {
  public Health health() {
    return Health.down().withDetails("error", "Database unreachable").build();
  }
}

medium

A. Method should be annotated with @Override

B. withDetails() method does not exist, should be withDetail()

C. Method name should be checkHealth() instead of health()

D. Health.down() cannot be used in custom indicators

Solution

1. Step 1: Check method signature and annotations

   The method correctly named health() matches interface; @Override annotation is optional but recommended.

2. Step 2: Verify method calls on Health builder

   The method withDetails() does not exist; correct method is withDetail() for adding one detail.

3. Final Answer:

   withDetails() method does not exist, should be withDetail() -> Option B

4. Quick Check:

   Use withDetail() to add single detail [OK]

Hint: Use withDetail() not withDetails() to add details [OK]

Common Mistakes:

• Missing @Override annotation (not error but best practice)
• Wrong method name instead of health()
• Thinking Health.down() is invalid

5. You want to customize the health endpoint to show "UP" only if both database and cache are reachable. Which approach correctly implements this logic?

hard

A. Use two separate HealthIndicator classes without combining results

B. Return Health.up() always and add details for database and cache status

C. Return Health.down() always and ignore individual checks

D. Return Health.up() if both checks pass; else Health.down() with details for each failure

Solution

1. Step 1: Understand combined health logic

   The health status should be UP only if both database and cache are reachable; otherwise DOWN.

2. Step 2: Implement conditional return with details

   Return Health.up() if both pass; else return Health.down() and include details explaining which failed.

3. Final Answer:

   Return Health.up() if both checks pass; else Health.down() with details for each failure -> Option D

4. Quick Check:

   Combined checks control status UP or DOWN with details [OK]

Hint: Return UP only if all checks pass; else DOWN with failure details [OK]

Common Mistakes:

• Returning UP regardless of failures
• Ignoring combined status logic
• Splitting checks without combining results