How do you create custom health indicators in Spring Boot?

Table of Contents

Introduction

In a Spring Boot application, health checks are crucial for monitoring the application's operational status. Spring Boot Actuator provides built-in health indicators that monitor the overall health of your application, such as database connections, disk space, and other system properties. However, you might want to monitor additional components that are unique to your application or infrastructure, such as a third-party service, custom APIs, or other application-specific metrics.

This is where custom health indicators come into play. By implementing the HealthIndicator interface, you can create custom health checks to monitor specific parts of your application and integrate them into Spring Boot’s existing health monitoring system.

In this guide, we’ll walk through the process of creating custom health indicators in Spring Boot.

What is a HealthIndicator?

The HealthIndicator interface is part of Spring Boot Actuator and is used to represent a single health check for your application. When implementing a custom health check, your health indicator must return a Health object, which encapsulates the status of the check (e.g., UP, DOWN, OUT_OF_SERVICE, or UNKNOWN), along with any optional details.

The HealthIndicator interface has a single method, health(), that performs the health check and returns a Health object:

You can use this method to define custom logic to determine whether a service, resource, or application component is healthy.

Steps to Create a Custom Health Indicator

Here’s how you can create and integrate a custom health indicator in your Spring Boot application:

1. Add Spring Boot Actuator Dependency

Before creating custom health indicators, ensure that you have Spring Boot Actuator added to your project. If not, add the following dependency to your pom.xml:

The Spring Boot Actuator will automatically expose the /actuator/health endpoint, which will aggregate all health checks, including custom ones.

2. Implement the Custom Health Indicator

To create a custom health indicator, implement the HealthIndicator interface and override the health() method. Inside the health() method, implement the logic for checking the health of your custom component or service.

Example 1: Custom Health Indicator for a Database Connection

Let’s create a custom health indicator to monitor the connection to a database (e.g., MySQL).

In this example:

  • If the database connection is established successfully, the health check will return UP.
  • If there’s any issue with the database connection, it will return DOWN, along with an error message.
Example 2: Custom Health Indicator for an External API

Another common use case for a custom health indicator is checking whether an external API or third-party service is available.

In this example:

  • The ExternalApiHealthIndicator performs a GET request to the API health check endpoint.
  • If the response contains the status "OK", the health indicator returns UP.
  • If the service is unreachable or returns an unexpected response, the health indicator returns DOWN.

3. Register the Custom Health Indicator

By annotating the custom health indicator class with @Component, it will automatically be registered as a Spring bean. Spring Boot Actuator will automatically detect and include it in the list of health indicators when you access the /actuator/health endpoint.

Alternatively, if you do not want to use the @Component annotation, you can register your health indicator explicitly in a @Configuration class:

4. Accessing the Health Status

Once the custom health indicator is implemented, it will automatically be included in the /actuator/health endpoint. You can access the health status of your application by navigating to:

For example, the response might look like this:

In this case:

  • The database is healthy (UP).
  • The external API is unavailable (DOWN).

5. Securing the Health Endpoint

In production environments, you might want to secure access to the /actuator/health endpoint to prevent unauthorized users from seeing sensitive application health data.

You can configure Spring Security to protect the /actuator/health endpoint as follows:

**application.properties**:

**SecurityConfig.java**:

This configuration will ensure that only users with the ADMIN role can access the /actuator/health endpoint, and the health details will only be shown when authorized.

Benefits of Creating Custom Health Indicators

  1. Tailored Monitoring: Custom health indicators allow you to monitor specific parts of your system that are critical to your application’s success, like external services, APIs, or custom business logic.
  2. Flexibility: You can implement any logic you need to monitor the health of your application’s components. Whether it's checking database health, verifying network connectivity, or ensuring a third-party API is responsive, custom health indicators offer great flexibility.
  3. Visibility: Custom health checks integrate seamlessly into Spring Boot Actuator’s /health endpoint, providing a unified view of your application’s health status in a centralized dashboard.
  4. Early Detection of Issues: By having custom health checks for crucial components, you can quickly detect and address issues before they affect users, ensuring high availability and reliability.

Conclusion

Creating custom health indicators in Spring Boot is a straightforward process that allows you to extend the health monitoring capabilities of your application. By implementing the HealthIndicator interface, you can monitor custom components or external dependencies and integrate them into Spring Boot Actuator’s health check system. This ensures that you can track the status of your entire application and respond proactively to potential issues.

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