Lesson 16 · Spring Boot · completes the course 🎓

Spring Boot Actuator

Production-ready endpoints for health, metrics and info — and the exposure rules the exam loves to test.

What you'll be tested on The difference between an endpoint being enabled vs exposed; the default exposure over HTTP vs JMX; how to expose more; the health statuses and how to customise health and metrics.

What Actuator gives you

Add spring-boot-starter-actuator and Boot exposes endpoints that report on and let you manage a running app — health, info, metrics, beans, env, loggers, mappings, threaddump, shutdown, and more. Over HTTP they live under the base path /actuator (e.g. /actuator/health).

Enabled vs exposed — the key distinction

Every endpoint has two independent switches:

Concern	Means	Default
Enabled	the endpoint bean exists at all	All enabled except `shutdown`
Exposed (HTTP)	reachable over the web	Only `health`
Exposed (JMX)	reachable over JMX	All endpoints

The classic exam question Over HTTP, only health is exposed by default. Over JMX, all endpoints are. An endpoint can be enabled but not exposed — it exists, but you can't reach it over HTTP until you include it. And shutdown is the one endpoint disabled by default.

Exposing more endpoints

# expose everything over HTTP
management.endpoints.web.exposure.include=*

# or a specific set, and exclude some
management.endpoints.web.exposure.include=health,info,metrics
management.endpoints.web.exposure.exclude=env,beans

The health endpoint

Aggregates health indicators (database, disk space, etc.) into one overall status.
Statuses: UP, DOWN, OUT_OF_SERVICE, UNKNOWN. Severity order is configurable via management.endpoint.health.status.order.
Full details are hidden by default — management.endpoint.health.show-details = never (default), when-authorized, or always.
Add your own check by implementing HealthIndicator (its health() returns a Health).

@Component
public class QueueHealthIndicator implements HealthIndicator {
  @Override public Health health() {
    return queueOk() ? Health.up().build()
                     : Health.down().withDetail("queue", "full").build();
  }
}

Metrics & securing endpoints

Metrics are powered by Micrometer. Record custom metrics by injecting a MeterRegistry and creating counters/gauges/timers.
Securing: Actuator endpoints are just URLs — protect them with Spring Security (Lesson 14), e.g. restrict /actuator/** to an ADMIN role.
Move endpoints to a separate port with management.server.port, or change the base path with management.endpoints.web.base-path.

Primary source — read this

Spring Boot 2.5 — Actuator: Exposing Endpoints, Health & Metrics

Read "Enabling/Exposing Endpoints" (the default table), "Health Information", and "Metrics".

Check yourself

The exposure defaults and the enabled-vs-exposed distinction are the money questions. All answers verified against the Boot 2.5 docs. Options shuffle on every load.

🎓 That's the whole course You've now covered all six exam sections — Core, Data, MVC, Testing, Security, and Boot (with Actuator). Second pass: your book's Boot Actuator section. Then move to the full-length mock in the book.

I'm your teacher — ask me anything. Now take the Full Mock Exam → — 60 questions, a 130-minute timer, all six sections, scored under real conditions. Tell me your weakest section and I'll drill it. And when you sit the exam — good luck. You've earned the confidence.

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