What is Actuator? Common endpoints: /health, /info, /metrics, /env, /loggers, /threaddump, /heapdump.

Actuator is the Spring Boot starter that exposes operational endpoints for monitoring and managing a running application — health checks, metrics, environment, loggers, thread and heap dumps — over HTTP (or JMX) under the /actuator base path. You get it by adding one dependency:

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

The common endpoints

• /health — aggregate UP/DOWN status assembled from all HealthIndicator beans (datasource, disk space, Redis, …). The one endpoint your orchestrator polls.
• /info — arbitrary descriptive metadata: build version, git commit, custom key/values.
• /metrics — Micrometer meters; list names at /metrics, drill into one with /metrics/jvm.memory.used.
• /env — the resolved Environment: every property source and value. Includes secrets, so it is sensitive.
• /loggers — view and change log levels at runtime with a POST, no restart. Hugely useful for debugging production: POST /actuator/loggers/com.acme {"configuredLevel":"DEBUG"}.
• /threaddump — a full JVM thread dump for diagnosing deadlocks and stuck threads.
• /heapdump — downloads a binary .hprof heap dump for memory-leak analysis. Heavy and sensitive.
• /prometheus — metrics in Prometheus scrape format (when the Prometheus registry is on the classpath).

The default you must know

By default, only /health and /info are exposed over HTTP. All others are enabled but not web-exposed; you opt in explicitly:

management:
  endpoints:
    web:
      exposure:
        include: health,info,metrics,loggers,prometheus

exposure.exclude blacklists, and * exposes everything (never in production). Endpoints can also be individually enabled/disabled via management.endpoint.<id>.enabled.

The base path defaults to /actuator and is configurable with management.endpoints.web.base-path. Each endpoint also surfaces over JMX independently of HTTP exposure.