Top Quarkus Interview Questions Every Java Developer Should Know (2025 Edition)
Master Quarkus fundamentals, reactive APIs, native builds, and AI integrations with this comprehensive, real-world interview guide for modern Java developers.
When I first started talking about Quarkus, one question was always asked first by curious developers: Where can I find Quarkus interview questions? I love learning this way and they usually help me with preparations. As a matter of fact, there’s no official set of interview questions. Every team makes their own, often reinventing the wheel. So I decided to compile this fundamental collection based on real-world projects, community experience, and the many tutorials I’ve published on The Main Thread.
If you’re preparing for a Quarkus interview, hiring someone who claims to be a Quarkus expert, or just looking for a new way of learning Quarkus, this guide gives you a clear, structured view of what to ask and what to expect.
It covers everything from core architecture to reactive programming, native compilation, Dev Services, and advanced performance tuning couple of AI.
Each section includes further reading links to deeper hands-on tutorials.
Quarkus Fundamentals
Q: What is Quarkus and what problems does it solve?
Quarkus is a cloud-native Java framework designed for fast startup, low memory usage, and cloud efficiency. It rethinks traditional Java by moving much of the heavy lifting to build time.
Q: How does Quarkus differ from Spring Boot or Micronaut?
Quarkus performs build-time metadata processing, resulting in smaller, faster, and more memory-efficient apps.
See: What Spring Didn’t Teach You: Becoming a Modern Java Developer with Quarkus
Q: What are the two runtime modes of Quarkus?
JVM mode – standard execution on the JVM
Native mode – compiled with GraalVM for instant startup
Q: How does Quarkus achieve fast startup?
By analyzing classes, annotations, and configuration at build time instead of runtime.
Q: What role does GraalVM play in Quarkus?
It compiles your application into a native binary, removing the JVM startup overhead.
Dependency Injection (CDI & ArC)
Q: What DI framework does Quarkus use?
Quarkus uses ArC, its own implementation of Jakarta CDI lite.
Q: What CDI scopes are available?@ApplicationScoped, @RequestScoped, @Dependent, and @Singleton.
Q: How do you inject configuration in Quarkus?
With @ConfigProperty from MicroProfile Config.
Q: Difference between @Singleton and @ApplicationScoped?@ApplicationScoped beans can be proxied and follow CDI semantics. @Singleton beans are simpler and not proxied.
See: Understanding CDI in Quarkus
REST & Reactive APIs
Q: What are the two ways to build REST APIs in Quarkus?
REST (blocking, JAX-RS)
REST Reactive (non-blocking, event-loop friendly)
Both on the same stack!
Q: What is Mutiny?
The reactive programming library in Quarkus. It introduces Uni<T> and Multi<T> types, similar to Mono and Flux in Reactor.
Q: How do you handle blocking calls in a reactive route?
Use the @Blocking annotation to delegate work to a worker thread.
Q: What are the advantages of Quarkus REST?
Faster throughput, lower latency, and scalability under load.
See: Reactive Java with Quarkus Simplified
Data & Persistence
Q: Which ORMs are supported?
Hibernate ORM and Hibernate Reactive with Panache.
Q: What is Panache?
An abstraction layer that simplifies JPA with active record and repository patterns.
Q: How does Quarkus manage transactions?
With @Transactional, supporting both blocking and reactive contexts.
Q: How are database migrations handled?
Through Flyway or Liquibase extensions.
See: Mastering Transactions in Quarkus
Configuration & Profiles
Q: How does configuration work in Quarkus?
Through MicroProfile Config. Values can come from files, environment variables, or system properties.
Q: What are profiles in Quarkus?
Profiles (%dev, %test, %prod) allow environment-specific settings.
Q: Can you create custom profiles?
Yes, by setting quarkus.profile in application.properties.
Q: How do you externalize configuration?
Use ConfigMapping, ConfigSource, or Kubernetes Secrets.
See: Quarkus Questions Answered
Testing
Q: What test annotations does Quarkus provide?
@QuarkusTest– JVM tests@QuarkusIntegrationTest– Opaque Box Tests
Q: How do you mock beans in tests?
Use @InjectMock or QuarkusMock.installMockForType().
Q: What is continuous testing in Quarkus?
Dev mode automatically reruns tests after every change.
See: Testing Rest APIs in Quarkus
Native Compilation & Performance
Q: What are native image limitations?
Dynamic class loading and reflection can fail unless explicitly registered.
Q: How do you register reflection classes?
Using @RegisterForReflection or a reflect-config.json file.
Q: How does Quarkus optimize at build time?
Dead-code elimination, constant folding, and resource preloading.
Q: How do you analyze startup performance?
Enable startup metrics or use -Dquarkus.profile=prod for profiling.
See: The Secret to Quarkus Performance
Microservices & Cloud-Native
Q: How does Quarkus support microservices?
With MicroProfile, SmallRye, and Kubernetes-native extensions.
Q: What is SmallRye?
An implementation of MicroProfile specs (Config, Fault Tolerance, Metrics, etc.).
Q: How do you expose health and readiness probes?
Using @Liveness, @Readiness, and @Startup.
Q: How does Quarkus integrate with Kubernetes or OpenShift?
Automatically generates manifests when you add the Kubernetes extension.
See: Deploy Java Like A Pro on OpenShift
Security
Q: What security options are available?
Quarkus supports Basic Auth, OAuth2, OIDC, and JWT RBAC.
Q: How do you secure endpoints?
Use annotations like @RolesAllowed, @Authenticated, and inject SecurityIdentity.
Q: What is Quarkus Security JPA?
A simple username/password store backed by JPA entities.
See: The Secret Agent’s Guide to API Key & Token Management
Advanced Topics
Q: What is Dev Services?
Automatic provisioning of databases, Kafka, or Redis using Testcontainers.
Q: How does Quarkus support messaging?
Via SmallRye Reactive Messaging with Kafka, AMQP, or in-memory channels.
Q: What is an extension in Quarkus?
A modular plugin that adds capabilities at build and runtime.
Q: How does Quarkus handle observability?
Through OpenTelemetry, Micrometer, and Structured Logging.
See: Centralized Log Management with Quarkus
AI and LangChain4j Integration
Q: How can Quarkus be used to integrate Large Language Models (LLMs) into Java applications?
Quarkus supports AI integration through the LangChain4j extension, which provides declarative APIs for calling and orchestrating LLMs. Developers can connect to local models via Ollama or cloud models like OpenAI or Bedrock, leveraging CDI-managed AI services for safe, repeatable inference.
See: Quarkus + LangChain4j: Build AI-Infused Java Applications
Q: What is LangChain4j and how does it relate to Quarkus?
LangChain4j is a Java library that helps build AI-powered applications using composable building blocks—prompt templates, memory, tool calls, and model orchestration. Quarkus provides first-class support through the quarkus-langchain4j extension, integrating configuration, dependency injection, and Dev Services for local model setup.
See: Agentic AI Explained for Beginners
Q: How do you serve local AI models within a Quarkus application?
Use Ollama with Dev Services to automatically start a local model container. Quarkus LangChain4j will detect the model endpoint and configure it dynamically during development.
See: Running Local LLMs with Quarkus and Ollama
Q: What are common patterns for managing context and memory in AI-infused Quarkus apps?
Use persistent chat memory (e.g., PostgreSQL + Panache) and vector stores (pgvector or Redis) to maintain conversational state and retrieve relevant documents. These patterns are crucial for Retrieval-Augmented Generation (RAG) pipelines.
See: Building a Self-Organizing AI Memory with Quarkus
Q: How would you implement guardrails for AI output in Quarkus?
Use LangChain4j guardrails or input/output validators to ensure safe responses. For example, intercept and reject model outputs that violate business policies or contain sensitive data.
See: Guardrails for LLM Prompts in Quarkus
Q: What is the Model Context Protocol (MCP), and why is it relevant for Quarkus developers?
The MCP standardizes communication between LLMs and external tools. With quarkus-mcp-server extensions, Quarkus can act as a tool provider, exposing APIs or databases as structured actions callable by AI agents.
See: Building MCP Servers with Quarkus
Q: How would you deploy an AI-infused Quarkus application to Kubernetes?
Containerize it with quarkus-container-image-jib and include GPU resource configuration or model-serving sidecars (like Ollama or vLLM). The manifests can be generated automatically using the kubernetes extension.
Q: How do Quarkus build-time optimizations help with AI workloads?
They reduce cold start latency for model inference endpoints and make tool-calling agents deployable on lightweight environments such as edge devices or serverless functions.
Scenario-Based Questions
Scenario 1: Your native Quarkus app fails to start with reflection errors.
→ Check for missing @RegisterForReflection classes. Use --verbose to inspect build logs.
Scenario 2: Migrating a Spring Boot app to Quarkus.
→ Start with Quarkus CLI, add the spring-web and spring-di compatibility extensions, test modules gradually.
Scenario 3: Your app shows high CPU under load.
→ Profile event loop threads, ensure blocking calls are annotated with @Blocking.
Scenario 4: Need to handle millions of requests efficiently.
→ Use REST + Mutiny, enable Vert.x event loops, monitor metrics with SmallRye.
See:
Quarkus is evolving fast.
Whether you’re prepping for a job or assessing candidates, these questions reflect real-world enterprise scenarios.
If you can answer most of them confidently, you’re ready for any Quarkus technical interview.
For hands-on practice, start with Learn Quarkus: A Microlearning Path for Java Developers.
Stay curious. Build small, deploy fast.