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spring-boot/spring-boot-project/spring-boot-actuator
Brian Clozel fd0b2f6695 Add Kubernetes Liveness and Readiness Probes support
Prior to this commit and as of Spring Boot 2.2.0, we would advise
developers to use the Actuator health groups to define custom "liveness"
and "readiness" groups and configure them with subsets of existing
health indicators.

This commit addresses several limitations with that approach.

First, `LivenessState` and `ReadinessState` are promoted to first class
concepts in Spring Boot applications. These states should not only based
on periodic health checks. Applications should be able to track changes
(and adapt their behavior) or update states (when an error happens).

The `ApplicationStateProvider` can be injected and used by applications
components to get the current application state. Components can also
track specific `ApplicationEvent` to be notified of changes, like
`ReadinessStateChangedEvent` and `LivenessStateChangedEvent`.
Components can also publish such events with an
`ApplicationEventPublisher`. Spring Boot will track startup event and
application context state to update the liveness and readiness state of
the application. This infrastructure is available in the
main spring-boot module.

If Spring Boot Actuator is on the classpath, additional
`HealthIndicator` will be contributed to the application:
`"LivenessProveHealthIndicator"` and `"ReadinessProbeHealthIndicator"`.
Also, "liveness" and "readiness" Health groups will be defined if
they're not configured already.

Closes gh-19593
5 years ago
..
src Add Kubernetes Liveness and Readiness Probes support 5 years ago
README.adoc Revisit documentation that mentions Gradle "compile" configuration 5 years ago
build.gradle Add R2BC connection pool metrics 5 years ago

README.adoc

= Spring Boot - Actuator

Spring Boot Actuator includes a number of additional features to help you monitor and
manage your application when it's pushed to production. You can choose to manage and
monitor your application using HTTP or JMX endpoints. Auditing, health and metrics
gathering can be automatically applied to your application. The
https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#production-ready[user guide]
covers the features in more detail.

== Enabling the Actuator
The simplest way to enable the features is to add a dependency to the
`spring-boot-starter-actuator` '`Starter`'. To add the actuator to a Maven-based project,
add the following '`Starter`' dependency:

[source,xml,indent=0]
----
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-actuator</artifactId>
		</dependency>
	</dependencies>
----

For Gradle, use the following declaration:

[indent=0]
----
	dependencies {
		implementation 'org.springframework.boot:spring-boot-starter-actuator'
	}
----

== Features
* **Endpoints** Actuator endpoints allow you to monitor and interact with your
  application. Spring Boot includes a number of built-in endpoints and you can also add
  your own. For example the `health` endpoint provides basic application health
  information. Run up a basic application and look at `/actuator/health`.
* **Metrics** Spring Boot Actuator provides dimensional metrics by integrating with
  https://micrometer.io[Micrometer].
* **Audit** Spring Boot Actuator has a flexible audit framework that will publish events
  to an `AuditEventRepository`. Once Spring Security is in play it automatically publishes
  authentication events by default. This can be very useful for reporting, and also to
  implement a lock-out policy based on authentication failures.