How do you create a custom health indicator in Spring Boot?

Table of Contents

• Introduction
• Creating a Custom Health Indicator
  • 1. Implementing the **HealthIndicator** Interface
  • 2. Explanation of the Code
  • 3. Accessing Custom Health Indicator via Actuator
  • 4. Customizing Health Indicator with Severity
  • 5. Registering Multiple Custom Health Indicators
  • 6. Testing Your Custom Health Indicator
  • 7. Security Considerations
• Practical Example: Full Code for a Custom Health Indicator
  • 8. Viewing the Health Endpoint
• Conclusion

Introduction

In Spring Boot applications, health checks are essential for monitoring the health and status of the application in production environments. Spring Boot Actuator provides a variety of built-in health checks (like checking database connectivity or disk space), but sometimes you may need to implement a custom health check for your specific use case. A custom health indicator allows you to integrate your application’s specific logic into the Spring Boot health check system.

A custom health indicator can be used to monitor things like:

• External services.
• APIs or endpoints.
• Business logic that’s critical for your application.

In this guide, we'll show you how to create a custom health indicator in Spring Boot using the HealthIndicator interface.

Creating a Custom Health Indicator

1. Implementing the **HealthIndicator** Interface

To create a custom health indicator, you need to implement the HealthIndicator interface provided by Spring Boot Actuator. This interface requires you to override the health() method, where you define the logic to check the health status of your application.

Here’s the basic structure of a custom health indicator:

2. Explanation of the Code

• HealthIndicator interface: This is the interface you need to implement to create a custom health indicator. It contains a single method, health(), which returns a Health object.
• **health()** method: This is where you define the logic to check the health of a component or service. In the example, the method checks the status of some service (could be a database, an external API, or any application-specific logic).
• Health Status: You can return either a healthy (Health.up()) or unhealthy (Health.down()) status. You can also add extra details using the withDetail() method, which will include additional information in the response.
• **@Component** annotation: The @Component annotation ensures that Spring Boot automatically discovers and registers the health indicator as a Spring Bean. If you're using Spring Boot's component scanning, it will automatically find this class.

3. Accessing Custom Health Indicator via Actuator

Once you’ve implemented your custom health indicator, it will be automatically registered by Spring Boot Actuator, and you can access it through the /actuator/health endpoint.

Here’s an example of how the output might look after implementing a custom health indicator:

Example Response:

If your health check logic fails, the status will change to "DOWN":

4. Customizing Health Indicator with Severity

In addition to the basic up() and down() statuses, Spring Boot allows you to customize the health status further by adding a severity level. You can use Health.outOfService() or Health.unknown() to represent the status of your service more accurately.

For example:

5. Registering Multiple Custom Health Indicators

You can create multiple custom health indicators in your application. Each indicator can be responsible for monitoring a different aspect of your system. Spring Boot will automatically discover and expose all of them.

With this setup, both MyCustomHealthIndicator and AnotherCustomHealthIndicator will be exposed in the /actuator/health endpoint.

6. Testing Your Custom Health Indicator

To test the custom health indicator, you can use tools like Postman or a simple browser to access the /actuator/health endpoint of your application.

Assuming the Spring Boot application is running on port 8080, you can visit:

You should see the health status of your custom service along with any other built-in health checks provided by Actuator.

7. Security Considerations

By default, Actuator endpoints, including /actuator/health, are publicly accessible. However, in production environments, you may want to secure these endpoints to prevent unauthorized access. You can use Spring Security to configure role-based access to Actuator endpoints.

For example, to require authentication for health endpoints:

This will secure the /actuator/health endpoint and require authentication with the username and password specified.

Practical Example: Full Code for a Custom Health Indicator

Here’s the full code for a custom health indicator checking the status of a hypothetical external service:

8. Viewing the Health Endpoint

Once your custom health indicator is set up, you can view it at:

The response might look like this:

Conclusion

Creating a custom health indicator in Spring Boot is a straightforward process that allows you to extend the built-in health checks provided by Spring Boot Actuator. By implementing the HealthIndicator interface, you can integrate custom logic for monitoring your application's health, whether it's checking external services, APIs, or critical application components. With the flexibility to add custom metrics and detailed information, you can ensure that your application’s health status is accurately monitored and easily accessible through the Actuator endpoints.