20 Akka Interview Questions and Answers

Akka is a toolkit and runtime for building highly concurrent, distributed, and resilient message-driven applications on the JVM. Akka is written in Scala and used by many companies including LinkedIn, Twitter, and the Guardian.

If you’re interviewing for a position that uses Akka, you can expect to be asked questions about your experience with the toolkit and your understanding of how it works. In this article, we’ll review some of the most common Akka interview questions and provide guidance on how to answer them.

Akka Interview Questions and Answers

Here are 20 commonly asked Akka interview questions and answers to prepare you for your interview:

1. What is Akka?

Akka is a toolkit and runtime for building highly concurrent, distributed, and resilient message-driven applications on the JVM.

2. How would you describe the reactive programming model?

The reactive programming model is a way of programming that is based on asynchronous message-passing. This means that instead of having one thread of execution, there are multiple threads that can communicate with each other by passing messages. This can make it easier to write concurrent and parallel programs.

3. Can you explain what a message broker in context with Akka is?

A message broker is a piece of software that helps facilitate communication between different parts of a system by routing messages between them. In the context of Akka, a message broker can be used to route messages between actors, or between different Akka systems.

4. What are some of the main features and benefits of using Akka?

Akka is a toolkit and runtime for building highly concurrent, distributed, and resilient message-driven applications on the JVM. Akka is designed to work with both Java and Scala, and it integrates with popular build tools like Maven and sbt. Akka is used in a variety of applications, including big data, Internet of Things, microservices, and more. Some of the main benefits of using Akka include its ability to handle high throughput and low latency, its scalability, and its fault tolerance.

5. Is it possible to use multiple actors per thread? If yes, then how?

Yes, it is possible to use multiple actors per thread. In order to do this, you will need to create a new ActorSystem for each thread that you wish to use actors on.

6. Why do you think Akka is more efficient than other solutions for handling concurrency?

Akka is more efficient than other solutions for handling concurrency because it uses a message-passing model to communicate between actors. This means that there is no need for locks or other synchronization mechanisms, which can lead to deadlocks. Additionally, Akka can be used on a distributed system, which further increases its efficiency.

7. What are routers and routees in the context of Akka?

Routers are components in Akka that are responsible for routing messages to the correct destination, while routees are the actual destinations that the messages are routed to. In order for a router to know where to route a message, it needs to have a list of routees that it can choose from. When a message is sent to a router, the router will select one of the routees from its list and send the message to that routee.

8. Can you explain how supervision works when using Akka?

Supervision is a mechanism for handling errors and restarting actors in Akka. When an actor fails, the supervisor will receive a message telling them what happened. The supervisor can then decide whether to restart the actor, stop the actor, or escalate the error to the parent supervisor.

9. Can you give me an example of how you would design a system where multiple actors can communicate with each other asynchronously?

There are a few different ways to design a system like this, but one approach would be to have each actor maintain a list of other actors that it can communicate with. When an actor wants to send a message to another actor, it would simply add the message to the list of messages that the other actor needs to process. The other actor would then process the message when it is able to.

10. What’s your understanding of actor paths in Akka?

Actor paths are used to uniquely identify each actor in an Akka system. The path consists of the actor’s name and the path to the actor’s mailbox. The actor’s name is used to identify the actor within the scope of the actor system, while the path to the mailbox is used to identify the actor across different actor systems.

11. Can you tell me some important methods that are provided by the Actor class?

Some important methods provided by the Actor class include the following:
– become: This method allows an actor to change its behavior, which is useful for implementing state machines.
– unbecome: This method allows an actor to revert back to its original behavior.
– receive: This method defines what an actor should do when it receives a message.
– sender: This method returns the actor who sent the current message.
– context: This method returns the actor’s context, which provides information about the actor’s environment.

12. What is the difference between a local and remote actor reference?

A local actor reference is a reference to an actor that is running on the same JVM as the actor that is holding the reference. A remote actor reference is a reference to an actor that is running on a different JVM.

13. What are the different types of messages that actors can send to each other?

Actors can send each other either synchronous or asynchronous messages. Synchronous messages are sent and received within the same actor, while asynchronous messages are sent to other actors.

14. What are the differences between Scala and Java when developing applications with Akka?

The main difference between Scala and Java when developing applications with Akka is that Scala is a functional programming language while Java is an object-oriented programming language. This means that Scala code is typically more concise and easier to read than Java code. Additionally, Scala provides some features that Java does not, such as support for higher-order functions and immutable data structures.

15. What is the best way to test actors?

There are a few different ways to test actors, but the best way depends on what you are trying to test. If you are trying to test the functionality of an actor, then you can use the Akka Testkit. This will allow you to test the actor in isolation, without having to worry about other actors in the system. If you are trying to test the interaction between actors, then you can use the Akka Persistence Testkit. This will allow you to test how actors interact with each other, and how they persist data.

16. What is the purpose of dispatchers in Akka?

Dispatchers are responsible for routing messages to actors. They determine which thread an actor runs on, and they can be configured to provide different guarantees with respect to message ordering and execution.

17. What are the different states an actor can be in?

There are four different states an actor can be in: created, started, suspended, and stopped.

18. What happens when an exception occurs while processing a message?

When an exception occurs while processing a message, the message is sent to the dead letter queue.

19. What are some key components of the Akka framework?

Akka is a toolkit and runtime for building highly concurrent, distributed, and resilient message-driven applications on the JVM. Akka is written in Scala and uses the Actor Model to provide a level of abstraction between the application code and the underlying hardware. The key components of Akka are:

– Actors: Actors are the basic building blocks of Akka applications. They are lightweight processes that can communicate with each other using messages.

– Dispatchers: Dispatchers are responsible for routing messages to the appropriate actors.

– Supervisors: Supervisors are responsible for monitoring and restarting actors in case of failure.

– Routers: Routers are responsible for routing messages to the appropriate actors in a round-robin fashion.

20. What is the main advantage of using Akka over traditional approaches to doing asynchronous processing?

The main advantage of using Akka is that it can provide much better performance than traditional approaches. Akka is able to do this by using a much more efficient message passing system than what is typically used. This allows for a much higher degree of parallelism, which can lead to significant speedups.