How do you implement custom health checks in Spring Boot?

Table of Contents

• Introduction
• Steps to Implement Custom Health Checks in Spring Boot
  • 1. Add Spring Boot Actuator Dependency
    • For Maven:
    • For Gradle:
  • 2. Create a Custom Health Check with @HealthIndicator
    • Example: Checking an External API
  • 3. Accessing Custom Health Checks
    • Example Health Check Response:
  • 4. Using **Health.Builder** for Advanced Health Checks
    • Example: Adding Custom Status Details
  • 5. Handling Different Health States
    • Example: Checking Database and External Service
• Conclusion

Introduction

In a Spring Boot application, health checks are essential for monitoring the application's state, particularly in production environments. By default, Spring Boot Actuator provides several built-in health checks (e.g., for the database, disk space, and JVM). However, you often need to implement custom health checks to monitor services that are specific to your application, such as external APIs, custom databases, or file systems. The @HealthIndicator annotation in Spring Boot allows you to define these custom health checks, integrate them with Spring Boot Actuator, and expose them via the /actuator/health endpoint.

This guide demonstrates how to implement custom health checks in Spring Boot, helping you track the status of critical components in your application.

Steps to Implement Custom Health Checks in Spring Boot

1. Add Spring Boot Actuator Dependency

First, ensure that your project has the Spring Boot Actuator dependency, which provides health check functionality, along with many other production-ready features.

For Maven:

For Gradle:

This will bring in the necessary components to expose health checks and other actuator endpoints.

2. Create a Custom Health Check with @HealthIndicator

Once the actuator dependency is added, you can start creating custom health checks by implementing the **HealthIndicator** interface and using the @Component annotation to mark the health check as a Spring-managed bean.

The HealthIndicator interface has a single method, **health()**, which contains the custom logic for your health check. You can use this method to check the status of a service, resource, or external dependency.

Example: Checking an External API

Here’s an example of creating a custom health indicator that checks the health of an external API.

In this example:

• The ExternalApiHealthIndicator class performs an HTTP request to an external API's health check endpoint.
• If the API responds with "OK", the health check returns a **UP** status.
• If the response is anything other than "OK" or an error occurs, the health check returns a **DOWN** status.

3. Accessing Custom Health Checks

Once your custom health checks are created, they are automatically exposed in the **/actuator/health** endpoint. By default, Spring Boot exposes several built-in health checks (like the database and disk space checks), and any custom checks you implement are included in the response.

To ensure that the health endpoint is exposed, add the following property to your application.properties or application.yml:

This will ensure that the /actuator/health endpoint is available, and your custom health check will be visible when accessing the endpoint.

Example Health Check Response:

In this example, the health check for the external API is listed as "Healthy".

4. Using **Health.Builder** for Advanced Health Checks

Spring Boot allows you to include additional information or custom status details in your health checks. You can use the **Health.Builder** to add more granular details, such as error messages, response times, or other metadata.

Example: Adding Custom Status Details

In this example:

• If the database connection is healthy, the response will include "Database": "Connected".
• If the database is down, it will include "Database": "Connection failed".

This can be useful for more detailed health information in the health check output.

5. Handling Different Health States

The Health class provides multiple states, including UP, DOWN, OUT_OF_SERVICE, and UNKNOWN. These states represent the overall health of a component.

• **Health.up()**: Indicates that the component is healthy and operating normally.
• **Health.down()**: Indicates that the component is unhealthy or unavailable.
• **Health.outOfService()**: Indicates that the component is temporarily out of service.
• **Health.unknown()**: Indicates that the status of the component is unknown.

You can customize the response based on the actual status of your services.

Example: Checking Database and External Service

In this example, a composite health check aggregates the results of multiple health indicators, and the overall health status is determined based on the individual components.

Conclusion

Implementing custom health checks using the @HealthIndicator annotation in Spring Boot is an essential practice for monitoring the health of critical components in your application. With Spring Boot Actuator, you can easily expose these health checks via the /actuator/health endpoint. This allows you to monitor the status of internal services, external APIs, databases, and more. Custom health checks improve your ability to detect and respond to issues early, providing valuable insights into your application's operational state.

By creating robust and meaningful health indicators, you can ensure that your Spring Boot application is production-ready and well-maintained, enhancing both application stability and performance monitoring.