How do you create custom metrics in Spring Boot Actuator?

Table of Contents

Introduction

Spring Boot Actuator offers a powerful set of tools for managing and monitoring Spring Boot applications. One of the most valuable features it provides is the ability to define custom metrics. Custom metrics allow you to track specific aspects of your application's behavior, performance, or business logic, which can help with monitoring, debugging, and optimizing your application.

In this guide, we'll explore how to create custom metrics in Spring Boot Actuator, register them, and expose them for monitoring purposes.

1. What are Custom Metrics?

In Spring Boot, metrics represent the numerical data that gives insight into the behavior of an application. These can include things like request counts, error rates, memory usage, and much more. Spring Boot provides built-in metrics such as HTTP request counts, JVM memory stats, and database connection metrics. However, sometimes you may need to track custom business metrics (e.g., number of orders processed, inventory levels, etc.).

Custom metrics can be exposed through the /actuator/metrics endpoint, where they can be visualized and monitored.

2. How to Create Custom Metrics

To create custom metrics, follow these steps:

Step 1: Add Required Dependencies

Ensure that the Spring Boot Actuator and Micrometer dependencies are added to your project.

If you're using Maven, add the following dependencies:

<dependency>    <groupId>org.springframework.boot</groupId>    <artifactId>spring-boot-starter-actuator</artifactId> </dependency> <dependency>    <groupId>io.micrometer</groupId>    <artifactId>micrometer-core</artifactId> </dependency>

Step 2: Define Custom Metrics

You can define custom metrics using **MeterRegistry** (provided by Micrometer). A **MeterRegistry** is used to register and manage various types of metrics.

For example, you might want to create a custom counter to track how many times a particular action is performed:

Explanation:

  • **MeterRegistry**: The MeterRegistry object is used to register and manage your custom metrics (in this case, a **Counter**).
  • **counter()**: The counter() method creates a custom metric of type Counter with specific tags. In the example, the counter is used to track the number of user logins, and the tag action=user_login is added for better categorization.
  • **increment()**: This method increments the counter each time a user logs in (or the relevant action occurs).

Step 3: Exposing Custom Metrics

Once you've defined your custom metric, it is automatically registered in the Micrometer registry. You can then expose it through the /actuator/metrics endpoint.

Make sure the following property is configured in your application.properties or application.yml to expose the necessary actuator endpoints:

Now, after calling incrementLoginCount() in your application, you can access the custom metric at the /actuator/metrics/custom_counter endpoint.

Example request:

The output would look like:

3. Types of Custom Metrics

Spring Boot supports a variety of metric types through Micrometer. You can create counters, gauges, timers, and more. Here’s a brief overview of each type:

1. Counter:

Counters are used for counting occurrences of events, such as how many times an action has been performed. This is a simple incremental metric.

2. Gauge:

Gauges measure values that can go up or down, such as the current number of active users or the current system load.

3. Timer:

Timers measure the time taken for a particular operation (e.g., the response time for an HTTP request or database query).

4. Distribution Summary:

A distribution summary is used to track the distribution of numeric values, such as request durations or sizes.

4. Visualizing and Monitoring Custom Metrics

Once your custom metrics are exposed, you can visualize and monitor them using various tools. For instance:

1. Prometheus Integration:

Spring Boot Actuator integrates with Prometheus to scrape metrics at regular intervals. To integrate Prometheus, add the Prometheus dependency and configure it to scrape /actuator/metrics.

You can then access the Prometheus metrics endpoint:

2. Grafana:

Grafana can be used to visualize Prometheus metrics by creating custom dashboards that include your Spring Boot custom metrics.

5. Securing Custom Metrics

It's essential to secure sensitive metrics, especially in production environments. You can restrict access to the /actuator/metrics endpoint using Spring Security.

Example: Securing Actuator Endpoints with Basic Authentication

This ensures that only authenticated users can access the custom metrics endpoints.

Conclusion

Creating custom metrics in Spring Boot Actuator allows you to monitor key aspects of your application and gain valuable insights into its performance. With the help of Micrometer, you can define various types of metrics—counters, gauges, timers, and distribution summaries—and expose them via the /actuator/metrics endpoint. These custom metrics can then be integrated with external monitoring systems like Prometheus and Grafana for more in-depth visualization and alerting.

Key Takeaways:

  • Micrometer provides an easy way to define custom metrics in Spring Boot.
  • Custom metrics can be exposed through the /actuator/metrics endpoint.
  • Various types of metrics such as counters, gauges, timers, and distribution summaries can be used.
  • Secure custom metrics endpoints to protect sensitive data.
  • Integrate with external monitoring tools like Prometheus and Grafana for advanced tracking and visualization.
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