Spring Boot Actuator Interview Questions and Answers

Master Spring Boot Actuator with interview questions covering health checks, endpoints, metrics, Micrometer, Prometheus, custom endpoints, monitoring, Kubernetes readiness/liveness probes, and production best practices.

Introduction

Modern enterprise applications must be observable in production.

Operations teams need answers to questions like:

Is the application healthy?
How much memory is being used?
What is the CPU usage?
How many HTTP requests are received?
Which endpoints are slow?
Is the database available?
Are Kafka and Redis connected?

Spring Boot Actuator provides production-ready monitoring and management capabilities through built-in endpoints.

Actuator is widely used with:

Micrometer
Prometheus
Grafana
ELK Stack
Datadog
Dynatrace
Kubernetes

Spring Boot Observability Architecture

flowchart LR

Client --> SpringBootApp

SpringBootApp --> Actuator

Actuator --> Micrometer

Micrometer --> Prometheus

Prometheus --> Grafana

Actuator --> HealthEndpoint

Actuator --> MetricsEndpoint

Actuator --> InfoEndpoint

Q1. What is Spring Boot Actuator?

Answer

Spring Boot Actuator is a production-ready module that exposes application monitoring and management endpoints.

It provides information about:

Health
Metrics
Environment
Beans
Mappings
Configuration
Loggers
Thread Dumps

Dependency

<dependency>

<groupId>
org.springframework.boot
</groupId>

<artifactId>
spring-boot-starter-actuator
</artifactId>

</dependency>

Q2. What are Actuator Endpoints?

Endpoints expose runtime information.

Common endpoints

Endpoint	Purpose
/actuator/health	Application health
/actuator/info	Application information
/actuator/metrics	Performance metrics
/actuator/env	Environment properties
/actuator/beans	Spring beans
/actuator/mappings	REST mappings
/actuator/loggers	Logging levels
/actuator/prometheus	Prometheus metrics

Architecture

flowchart TD

Actuator --> Health

Actuator --> Metrics

Actuator --> Beans

Actuator --> Loggers

Actuator --> Prometheus

Q3. What is the Health Endpoint?

The Health endpoint reports application status.

Example

GET

/actuator/health

Response

{
  "status":"UP"
}

Health indicators include

Database
Redis
Kafka
RabbitMQ
Disk Space
Elasticsearch

Q4. What is Micrometer?

Micrometer is Spring Boot's metrics abstraction library.

It collects metrics from

JVM
CPU
Memory
HTTP Requests
Database
Cache
Custom Metrics

Architecture

flowchart LR

Application --> Micrometer

Micrometer --> Prometheus

Micrometer --> Datadog

Micrometer --> CloudWatch

Micrometer --> Dynatrace

Micrometer allows one codebase to publish metrics to multiple monitoring systems.

Q5. What metrics does Actuator expose?

Common metrics

JVM Memory
CPU Usage
Heap Usage
Garbage Collection
HTTP Requests
Database Connections
Thread Count
Cache Statistics

Example

GET

/actuator/metrics

Retrieve a specific metric

/actuator/metrics/

jvm.memory.used

Q6. How does Prometheus integration work?

Spring Boot exposes metrics in Prometheus format.

Configuration

management.endpoints.web.exposure.include=

health,info,prometheus

Monitoring Flow

flowchart LR

SpringBoot --> Actuator

Actuator --> Prometheus

Prometheus --> Grafana

Grafana --> Dashboard

Prometheus periodically scrapes metrics from the application.

Q7. What are Custom Health Indicators?

Developers can implement custom health checks.

Example

@Component

public class PaymentHealthIndicator

implements HealthIndicator{

    @Override

    public Health health(){

        return Health.up().build();

    }

}

Typical custom checks

Payment Gateway
External REST API
Banking Core System
FTP Server
Cloud Storage

Q8. How do Liveness and Readiness Probes work?

Spring Boot supports Kubernetes probes.

Endpoints

/actuator/health/liveness

/actuator/health/readiness

Kubernetes Flow

flowchart LR

Kubernetes --> ReadinessProbe

ReadinessProbe --> SpringBoot

SpringBoot --> Database

SpringBoot --> Kafka

SpringBoot --> Redis

Purpose

Liveness determines whether the application should be restarted.
Readiness determines whether the application is ready to receive traffic.

Q9. How do you secure Actuator Endpoints?

Never expose all endpoints publicly.

Example

management.endpoints.web.exposure.include=

health,info

Secure with Spring Security.

Typical production exposure

health
info
prometheus

Restrict

beans
env
mappings
configprops

These endpoints may reveal sensitive information.

Q10. Actuator Best Practices

Enable Only Required Endpoints

Reduce attack surface.

Secure Management Endpoints

Require authentication for sensitive endpoints.

Use Micrometer

Collect standard and custom metrics.

Integrate with Prometheus

Use Grafana dashboards for visualization.

Monitor Business Metrics

Examples

Payments Processed
Failed Transactions
Active Users
Loan Requests

Banking Example

flowchart TD

BankingService --> Actuator

Actuator --> Health

Actuator --> Metrics

Actuator --> Prometheus

Prometheus --> Grafana

Grafana --> OperationsTeam

Operations teams monitor system health in real time.

Common Interview Questions

What is Spring Boot Actuator?
What are Actuator endpoints?
What is the Health endpoint?
What is Micrometer?
How does Prometheus integration work?
What metrics are available?
What are Custom Health Indicators?
What are Liveness and Readiness probes?
How do you secure Actuator?
Actuator best practices?

Quick Revision

Topic	Summary
Actuator	Production monitoring module
Health	Application status
Metrics	JVM, HTTP, Database metrics
Micrometer	Metrics abstraction
Prometheus	Metrics collection
Grafana	Visualization
HealthIndicator	Custom health checks
Readiness	Ready for traffic
Liveness	Should application restart?
Security	Protect sensitive endpoints

Actuator Request Lifecycle

sequenceDiagram
Prometheus->>Actuator: GET /actuator/prometheus
Actuator->>Micrometer: Collect Metrics
Micrometer-->>Actuator: Metrics
Actuator-->>Prometheus: Response
Prometheus->>Grafana: Store Metrics
Grafana-->>Operations Team: Dashboard

Production Example – Banking Payment Platform

A banking payment microservice processes 2 million transactions daily.

Production Monitoring Stack

Spring Boot Actuator exposes health and metrics.
Micrometer collects JVM, HTTP, HikariCP, and custom payment metrics.
Prometheus scrapes /actuator/prometheus every 15 seconds.
Grafana displays dashboards for CPU usage, response times, throughput, and failed transactions.
Kubernetes uses /actuator/health/liveness and /actuator/health/readiness to manage container lifecycle.
Spring Security restricts access to management endpoints.

flowchart LR

SpringBootApp --> Actuator

Actuator --> Health

Actuator --> Metrics

Actuator --> Prometheus

Prometheus --> Grafana

Grafana --> DevOps

Kubernetes --> LivenessProbe

Kubernetes --> ReadinessProbe

This monitoring architecture enables operations teams to detect failures, analyze performance, and maintain high availability.

Key Takeaways

Spring Boot Actuator provides production-ready monitoring and management endpoints.
Built-in endpoints expose application health, metrics, environment details, bean information, mappings, and logging configuration.
Micrometer serves as the metrics abstraction layer and integrates with monitoring systems such as Prometheus, Datadog, CloudWatch, and Dynatrace.
Prometheus collects metrics, while Grafana visualizes them through dashboards.
Custom HealthIndicator implementations allow applications to monitor external systems such as payment gateways and messaging platforms.
Kubernetes uses Liveness and Readiness probes to determine application lifecycle and traffic routing.
Only expose the endpoints required for production and secure sensitive endpoints using Spring Security.
Combining Actuator with Micrometer, Prometheus, and Grafana provides complete observability for enterprise Spring Boot applications.