Cách tạo custom HealthIndicator trong Spring Boot Actuator?

@Component("externalApi")
class ExternalApiHealthIndicator implements HealthIndicator {
  private final RestClient restClient;

  @Override public Health health() {
    try {
      var resp = restClient.get().uri("https://api.external.com/health")
        .retrieve().toEntity(String.class);
      return resp.getStatusCode().is2xxSuccessful()
        ? Health.up().withDetail("status", "reachable").build()
        : Health.down().withDetail("statusCode", resp.getStatusCode()).build();
    } catch (Exception e) {
      return Health.down(e).withDetail("message", "External API unreachable").build();
    }
  }
}

management.endpoint.health.group:
  liveness.include: livenessState
  readiness.include: readinessState, db, externalApi