How do you configure custom health indicators in Spring Boot?

Table of Contents

• Introduction
  • How Health Indicators Work in Spring Boot
  • Step-by-Step Guide to Creating Custom Health Indicators
    • 1. Implement the HealthIndicator Interface
    • 2. Register the Custom Health Indicator
    • 3. Access the Custom Health Indicator
  • Practical Example: Custom Health Indicator for File System
  • Additional Configuration and Customization
    • 1. Show Health Details
    • 2. Health Check Thresholds
    • 3. Customizing Health Status Codes
• Conclusion

Introduction

Health checks are an essential part of monitoring any production application. They help ensure that your application and its dependencies (like databases, messaging queues, etc.) are functioning correctly. Spring Boot, through the Spring Boot Actuator, provides a default set of health indicators, such as database health, disk space, and system health checks.

However, in many real-world applications, you might need to implement custom health checks to monitor application-specific conditions, such as the availability of third-party services, internal configurations, or business-critical processes.

Spring Boot Actuator allows you to create custom health indicators that extend the standard health checks. These custom indicators can then be included in the /actuator/health endpoint response, providing detailed health status for your application.

How Health Indicators Work in Spring Boot

In Spring Boot, health indicators are implemented using the HealthIndicator interface. This interface allows you to define the health status of a component, and Spring Boot aggregates all health indicators to create an overall application health report.

The health status can be one of the following:

• UP: The component is healthy and functioning correctly.
• DOWN: The component is unhealthy or failing.
• OUT_OF_SERVICE: The component is unavailable for use, usually due to planned maintenance.
• UNKNOWN: The health status could not be determined.

Spring Boot provides several built-in health indicators, like the DataSourceHealthIndicator (for database health) and DiskSpaceHealthIndicator (for disk space usage). You can extend the health check mechanism by creating your own custom HealthIndicator.

Step-by-Step Guide to Creating Custom Health Indicators

1. Implement the HealthIndicator Interface

To create a custom health indicator, you need to implement the HealthIndicator interface. This interface requires you to define a health() method that returns a Health object representing the health status of your component.

Here's an example of a custom health indicator that checks the availability of a third-party API:

In this example:

• We use a RestTemplate to make a request to the third-party API and check if it returns a healthy response.
• If the API responds positively, the health status is marked as UP.
• If there’s any exception (e.g., the API is unreachable), the health status is marked as DOWN.

2. Register the Custom Health Indicator

Once you have implemented the custom HealthIndicator, it will automatically be registered as a Spring Bean because of the @Component annotation. Spring Boot Actuator will detect all beans that implement the HealthIndicator interface and include them in the health check process.

3. Access the Custom Health Indicator

Once the custom health indicator is implemented and registered, it will be included in the /actuator/health endpoint response. You can access the health check as follows:

If your custom health indicator is UP, the output will look like this:

If it is DOWN or has any issues, the output might look like this:

Practical Example: Custom Health Indicator for File System

Let’s implement a custom health indicator to check the available space on a specific directory. This could be useful in scenarios where your application needs to ensure that there is enough disk space for file uploads or logs.

In this example:

• The custom health indicator checks the available space in a specific directory (/path/to/directory).
• If the available space is more than 1 GB, the health check is marked as UP.
• If the available space is below the threshold, it is marked as DOWN.

Additional Configuration and Customization

1. Show Health Details

By default, Spring Boot only shows the overall health status (UP/DOWN) in the /actuator/health endpoint. To show more details for health checks (such as the status of custom health indicators), configure the following property in your application.properties:

This will include detailed information for all health indicators in the health check response.

2. Health Check Thresholds

You can also specify thresholds for your custom health indicators, such as determining if a service or disk space falls below a certain threshold to mark the service as unhealthy. In this case, the threshold can be set dynamically via configuration properties:

You can inject and use this property within your custom health indicator.

3. Customizing Health Status Codes

You can also return custom health statuses, such as OUT_OF_SERVICE or UNKNOWN, based on your business logic or application needs:

Conclusion

Configuring custom health indicators in Spring Boot allows you to monitor the health of specific components or services within your application. By implementing the HealthIndicator interface, you can easily define custom checks for external services, disk space, database connections, and more. These custom indicators are automatically included in the /actuator/health endpoint, providing you with valuable insights into the application's health and performance.

Using Spring Boot Actuator and custom health indicators ensures that your application can be monitored effectively, improving reliability and helping you detect issues early.