Spring boot actuator

In this article, we introduce the Spring Boot Actuator, take a look at how to customize the Spring Boot Actuators’ /info endpoint and how to track and monitor this startup information.

1 Actuator

Actuator endpoints let you monitor and interact with your Spring Boot application.

1.1 Setup

By adding the following dependency to your project:

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-actuator</artifactId>
	</dependency>
</dependencies>

the actuator endpoints will become available in your project. : http://localhost:8080/actuator

Be aware that all actuators except for /health are disabled by default for security reasons. They might expose sensitive information. You can use the management.endpoints.web.exposure.include property to enable the actuators.

To expose all actuator endpoint :

management:
  endpoints:
    web:
      exposure:
        include: '*'

**To expose only info actuator endpoint :

management:
  endpoints:
    web:
      exposure:
        include: "info"

You can reach the info actuator on your local machine: http://localhost:8080/actuator/info once you start your Spring Boot application.

1.2 Spring Boot info actuator contributors

There are different info contributors that “contribute” to the information exposed by the actuator info endpoint:

build Enabled by default: true Goal: Exposes build information. Requires: you to generate build information Configuration property: management.info.build.enabled
env Enabled by default: false (since Spring Boot 2.6. For the older Spring Boot version, this contributor is enabled by default!) Goal: Exposes any property from the SpringEnvironment . Required: to specify properties with names that start with info.* in you application.yml or application.properties Configuration property: management.info.env.enabled
git Enabled by default: true Goal: exposes git information. Requires: you to generate git information Configuration property: management.info.git.enabled
java Enabled by default: false (since Spring Boot 2.6) Goal: exposes Java runtime information. Configuration property: management.info.java.enabled

1.3 Static Properties in /info

You can customize the environment info contributor by adding info.*properties to your application.yml or application.properties :

management.info:
  env.enabled: true
info:
  application:
    name: ${spring.application.name}
    description: spring actuator application
    version: '@project.version@'

1.4 GIT details in /info

We can add git details using the respective Maven dependency:

<dependency>
    <groupId>pl.project13.maven</groupId>
    <artifactId>git-commit-id-plugin</artifactId>
</dependency>

and enable management.info.git in configuration property:

management.info:
 git.enabled: true

1.5 GIT build information details in /info

We can also include build information including name, group, and version using the Maven plugin:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <executions>
        <execution>
            <goals>
                <goal>build-info</goal>
            </goals>
        </execution>
    </executions>
</plugin>

and enable management.info.build in configuration property:

management.info:
 build.enabled: true

2 Startup Tracking

Tracking the various steps during application startup can provide useful information that can help us to understand the time spent during various phases of application startup. Such instrumentation can also improve our understanding of the context lifecycle and the application startup sequence.

2.1 Setup

Add the spring-boot-starter-actuator dependency to our POM

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
  </dependency>
</dependencies>

Expose the required endpoint over HTTP by setting the configuration property in our application properties file:

management:
  endpoints:
    web:
      exposure:
        include: "startup"

2.2 Startup Endpoint

We need to set the application’s startup configuration to an instance of `BufferingApplicationStartup`. This is an in-memory implementation of the `ApplicationStartup` interface provided by Spring Boot. It captures the events during Spring’s startup process and stores them in an internal buffer.

Create a simple application with this implementation:

@SpringBootApplication
public class SpringActuatorApplication {
  public static void main(String[] args) {
    SpringApplication app = new SpringApplication(SpringActuatorApplication.class);
    app.setApplicationStartup(new BufferingApplicationStartup(2048));
    app.run(args);
  }
}

Now, we can start our application and query the startup actuator endpoint. http://localhost:8080/actuator/startup

Be aware before spring boot version 2.6 startup endpoint only allow POST method call.

2.3 Filtering Startup Events

The buffering implementation has a fixed capacity for storing events in memory. Therefore, it might not be desirable to store a large number of events in the buffer.

We can filter the instrumented events and only store those that may be of interest to us:

	public static void main(String[] args) {
		SpringApplication app = new SpringApplication(SpringActuatorApplication.class);
		BufferingApplicationStartup startup = new BufferingApplicationStartup(2048);
		startup.addFilter(startupStep -> startupStep.getName().matches("spring.boot.application.starting"));
		app.setApplicationStartup(startup);
		app.run(args);
	}