ActiveMQ is a popular open-source Message Broker.  It is widely used for integration projects involving message based communication. For various jobs which involve Enterprise Application Integration (EAI), ActiveMQ is always among the top sought skills. Before going for an interview for any relevant integration role, this article about ActiveMQ Interview Questions and Answers will greatly help you to get yourself prepared for the interview and crack your job interview with confidence.

Top 20 ActiveMQ Interview Questions and Answers for Job Interview

While in another article,  I have already explained in detail about ActiveMQ concepts and Basics of ActiveMQ, this article will help you to understand ActiveMQ from Job interview perspective. ActiveMQ Interview Questions and Answers covered in this article should be helpful not only for entry level jobs but also in the interviews where intermediate as well as advanced level ActiveMQ Concepts of the candidates are being assessed.

1. What is the Use-case of ActiveMQ and How ActiveMQ helps in Integration Projects?

ActiveMQ can be a useful choice as a message broker for different types of integration projects where asynchronous messaging is required between different systems and applications. It can be used in scenarios where pub-sub messaging is needed and also for point to point communication scenarios.

As an example, Apache ActiveMQ as a message broker can be used for Healthcare projects, E-Commerce solutions, Financial Services domain and for plenty of other microservices based applications.

ActiveMQ helps achieving loosely coupled integration between heterogeneous applications and systems through its standardized messaging protocols.

2. What are ActiveMQ Queues and Topics and what is the difference between a queue and a topic in ActiveMQ?

ActiveMQ supports both point to point and publish subscribe messaging. In ActiveMQ, a topic is used for pub-sub messaging, where multiple subscribers can receive the same message sent to a single topic. On the other hand, queues are used for point-to-point messaging, where each message is consumed by a single recipient from a specific ActiveMQ queue.

3. How We can Achieve Message Persistence in ActiveMQ?

To avoid any loss of data due to system crashes or broker failure, ActiveMQ provides message persistence feature.  ActiveMQ supports several different message stores, including in-memory persistence , file-based persistence ,AMQP Persistence and JDBC-based stores.

4. What are the Supported Protocols by ActiveMQ?

Different type of protocols are supported by ActiveMQ including AMQP, STOMP, MQTT, OpenWire and WebSocket. With support of a variety of protocols, ActiveMQ helps integrating different types of legacy as well as latest technology enabled applications and systems in a very efficient and convenient manner.

5. How We can Monitor health and performance of ActiveMQ Broker?

ActiveMQ provides Advisory feature which helps in monitoring through real-time notifications of system events, such as connections, disconnections, and message delivery. It can be used to monitor the health and performance of the broker, as well as to detect and respond to potential problems.

6. How can we Achieve Load Balancing and Fault Tolerance in ActiveMQ?

ActiveMQ can be setup in a clustered environment which supports both load balancing and failover by allowing multiple brokers to be configured in a network of brokers (NOB) . In a clustered ActiveMQ environment, Clients can connect to any broker in the network.  Messages are routed automatically  to the appropriate broker based on configured rules. With clustering, ActiveMQ brokers are grouped in such a way that they provide a single logical broker to the clients in a seamless manner.

7. How does ActiveMQ handle message redelivery?

Message redelivery requirement can be fulfilled in ActiveMQ in different ways including delayed redelivery, exponential backoff, and dead-letter queues (DLQs). When a message fails to be delivered to a consumer, it can be configured to be automatically redelivered after a specified delay or sent to a dead-letter queue for further analysis.

8. How we can ensure Security in ActiveMQ Messaging?

In order to have secure messaging through ActiveMQ brokers, various security options can be availed. E.g. One way SSL or Mutual SSL to achieve secure and encrypted communication. For authentication, we can use basic authentication (username/password authentication) and we can also integrate with popular identity providers such as LDAP and Active Directory.

9. How We can deal with message priorities in ActiveMQ?

We can use the message header property (JMSPriority) to ensure that high priority and critical messages are delivered first. Using JMSPriority property, we can decide a priority of a message from 0 to 9.

9 is the highest, 0 is the lowest priority value.  4 is the default message priority value in ActiveMQ.

10. What is the usage of ActiveMQ Web Console?

ActiveMQ provides a graphical UI in the form of a web console.  It can be used to perform various monitoring and administrative tasks. E.g. you can perform user management, queues & topic management, message browsing and monitoring related activities using ActiveMQ Web Console from your browser.

11. What is a Dead Level Queue in ActiveMQ?

A DLQ (Dead Level Queue) is an ActiveMQ Queue which is used to store any dead messages which could not be delivered to the intended consumers. DLQ is a special queue provided by ActiveMQ for each destination (queue or topic). Messages once routed to Dead Level Queue can be analyzed to have troubleshooting and to have any other relevant analytical reports.

12. Why ActiveMQ Message Compression is used?

Message compression is used to reduce the message size and utilize the bandwidth in a better way. Message compression is recommended only in those use-cases where messages with large size are being sent with limited bandwidth available.

13. How can we filter ActiveMQ Messages?

JMS Message Selector can be used to filter messages based on their properties. It allows ActiveMQ message consumers to select only the messages of their interest that match specific criteria. The selector is specified using a SQL-like syntax and is evaluated by the broker when messages are sent to the consumer.

14. How Can we Ensure a message gets delivered to a subscriber even if the subscriber is unavailable when message was sent?

For this purpose, durable subscription is made. A durable subscription allows a subscriber to receive messages sent to a topic even if the subscriber is offline at the time of message delivery. When the subscriber reconnects, it will receive any messages sent to the topic while it was offline.

15. What is the difference between ActiveMQ and JMS?

JMS is a specification while ActiveMQ is an implementation of that specification. JMS API is a standard specification which is further enhanced, customized and utilized by various implementations and ActiveMQ is one of those implementations.

16. What is the role of the ConnectionFactory in ActiveMQ?

The ConnectionFactory is responsible for creating connections to the ActiveMQ broker, which can be used to send and receive messages. It encapsulates the details of creating and managing connections, providing a simple API for clients to use.

17. What is ActiveMQ Provides Flow Mechanism?

Flow of messages from producer to the broker and from the broker to the consumer is controlled through the Flow Control Mechanism provided by ActiveMQ. It helps to prevent message producers from overwhelming message consumers, which can lead to poor performance, increased message delivery times, and possible message loss.

18. What is Prefetch Policy in ActiveMQ?

On consumer side, prefetch policy helps ensuring that consumer is not flooded with too many messages which it can’t handle. Prefetch policy is a consumer-side flow control mechanism that allows the consumer to specify how many messages it wants to prefetch from the broker.

19. What is the difference between a producer and a consumer in ActiveMQ?

A producer is the one who sends messages to a destination (queue or topic) while a consumer is a client that receives messages from a queue or topic. Producers and consumers can be separate applications or parts of the same application. Both producer and consumer rely on the broker which sits in the middle of the two to enable message communication.

20. What is the difference between the OpenWire and STOMP protocols in ActiveMQ?

OpenWire is the native binary protocol used by ActiveMQ, providing high performance and a rich messaging API. STOMP, on the other hand, is a simple text-based protocol that can be used by clients written in a variety of languages and platforms.

That’s it from this article. I hope that the information will be useful for you in cracking relevant interview. Happy learning !