Top 90 Software Architecture Interview Questions And Answers

Question 1

What Is CAP Theorem?

Accepted Answer

**The CAP Theorem for distributed computing** was published by Eric Brewer. This states that it is not possible for a distributed computer system to simultaneously provide all three of the following guarantees:

1.  *Consistency* (all nodes see the same data even at the same time with concurrent updates )
2.  *Availability* (a guarantee that every request receives a response about whether it was successful or failed)
3.  *Partition tolerance* (the system continues to operate despite arbitrary message loss or failure of part of the system)

The CAP acronym corresponds to these three guarantees. This theorem has created the base for modern distributed computing approaches. Worlds most high volume traffic companies (e.g. Amazon, Google, Facebook) use this as basis for deciding their application architecture. It's important to understand that only two of these three conditions can be guaranteed to be met by a system.

Question 2

What Is Load Balancing?

Accepted Answer

**Load balancing** is simple technique for distributing workloads across multiple machines or clusters. The most common and simple load balancing algorithm is Round Robin. In this type of load balancing the request is divided in circular order ensuring all machines get equal number of requests and no single machine is overloaded or underloaded.  
  
**The Purpose of load balancing is to**  
  
*   Optimize resource usage (avoid overload and under-load of any machines)
*   Achieve Maximum Throughput
*   Minimize response time

**Most common load balancing techniques in web based applications are**

1.  Round robin
2.  Session affinity or sticky session
3.  IP Address affinity

Question 3

Why use WebSocket over HTTP?

Accepted Answer

A **WebSocket** is a continuous connection between client and server. That continuous connection allows the following:

1.  Data can be sent from server to client at any time, without the client even requesting it. This is often called server\-push and is very valuable for applications where the client needs to know fairly quickly when something happens on the server (like a new chat messages has been received or a new price has been udpated). A client cannot be pushed data over http. The client would have to regularly poll by making an http request every few seconds in order to get timely new data. Client polling is not efficient.

2.  Data can be sent either way very efficiently. Because the connection is already established and a webSocket data frame is very efficiently organized, one can send data a lot more efficiently that via an HTTP request that necessarily contains headers, cookies, etc...

Question 4

What is Domain Driven Design?

Accepted Answer

**Domain Driven Design** is a methodology and process prescription for the development of complex systems whose focus is mapping activities, tasks, events, and data within a problem domain into the technology artifacts of a solution domain.

It is all about trying to make your software a model of a real-world system or process.

Question 5

Why Do You Need Clustering?

Accepted Answer

*Clustering* is needed for achieving high availability for a server software. The main purpose of clustering is to achieve 100% availability or a zero down time in service. A typical server software can be running on one computer machine and it can serve as long as there is no hardware failure or some other failure. By creating a cluster of more than one machine, we can reduce the chances of our service going un-available in case one of the machine fails.  
  
Doing clustering does not always guarantee that service will be 100% available since there can still be a chance that all the machine in a cluster fail at the same time. However it in not very likely in case you have many machines and they are located at different location or supported by their own resources.

Question 6

Define Microservice Architecture

Accepted Answer

**Microservices**, aka **_Microservice Architecture_**, is an architectural style that structures an application as a collection of small autonomous services, modeled around a **business domain.**

Question 7

What Is A Cluster?

Accepted Answer

A cluster is group of computer machines that can individually run a software. Clusters are typically utilized to achieve high availability for a server software. Clustering is used in many types of servers for high availability.

*   **App Server Cluster**  
    An app server cluster is group of machines that can run a application server that can be reliably utilized with a minimum of down-time.
*   **Database Server Cluster**  
    An database server cluster is group of machines that can run a database server that can be reliably utilized with a minimum of down-time.

Question 8

What defines a software architect?

Accepted Answer

An **architect** is the captain of the ship, making the decisions that cross multiple areas of concern (navigation, engineering, and so on), taking final responsibility for the overall health of the ship and its crew (project and its members), able to step into any station to perform those duties as the need arises (write code for any part of the project should they lose a member). He has to be familiar with the problem domain, the technology involved, and keep an eye out on new technologies that might make the project easier or answer new customers' feature requests.

Question 9

What Is Scalability?

Accepted Answer

Scalability is the ability of a system, network, or process to handle a growing amount of load by adding more resources. The adding of resource can be done in two ways

*   **Scaling Up**  
    This involves adding more resources to the existing nodes. For example, adding more RAM, Storage or processing power.
*   **Scaling Out**  
    This involves adding more nodes to support more users.

Any of the approaches can be used for scaling up/out a application, however the cost of adding resources (per user) may change as the volume increases. If we add resources to the system It should increase the ability of application to take more load in a proportional manner of added resources.  
  
An ideal application should be able to serve high level of load in less resources. However, in practical, linearly scalable system may be the best option achievable. Poorly designed applications may have really high cost on scaling up/out since it will require more resources/user as the load increases.

Question 10

What do you mean by _lower latency interaction_?

Accepted Answer

**Low latency** means that there is very little delay between the time you request something and the time you get a response. As it applies to webSockets, it just means that data can be sent quicker (particularly over slow links) because the connection has already been established so no extra packet roundtrips are required to establish the TCP connection.

Top 90 Software Architecture Interview Questions

What Is CAP Theorem?

What Is Load Balancing?

What do you mean by lower latency interaction?

What Is A Cluster?

Why Do You Need Clustering?

What defines a software architect?

What does the expression “Fail Early” mean, and when would you want to do so?

What Is Scalability?

Why use WebSocket over HTTP?

Define Microservice Architecture

What do you understand by Clean Architecture approach?

What is Test Driven Development?

What is meant by the KISS principle?

What is Domain Driven Design?

Why is it a good idea for “lower” application layers not to be aware of “higher” ones?

What is a Model in DDD?

What is Domain in DDD?

In OOP, what is the difference between the Repository Pattern and a Service Layer?

Is Unit Of Work equals Transaction? Or it is more than that?

Explain the Single Responsibility Principle (SRP)?

What is difference between Fault Tolerance and Fault Resilience?

What is the difference between Concurrency and Parallelism?

What does program to interfaces, not implementations mean?

What is the difference between DTOs and ViewModels in DDD?

What Is Load Balancing Fail Over?

What are the DRY and DIE principles?

What does SOLID stand for? What are its principles?

Is it better to return NULL or empty values from functions/methods where the return value is not present?

Name some Performance Testing metrics to measure

"People who like this also like... ". How would you implement this feature in an e-commerce shop?

How can you keep one copy of your utility code and let multiple consumer components use and deploy it?

Name some Performance Testing best practices

Name some benefits of CQRS Pattern

Describe what is the Event Sourcing Pattern

Explain what is Interface Segregation Principle (ISP) in Clean Architecture and what are some of its benefits?

WebSockets vs Rest API for real time data? Which to choose?

What is the difference between Monolithic, SOA and Microservices Architecture?

What Is Session Replication?

What Is Middle Tier Clustering?

How Do you update a live heavy traffic site with minimum or Zero Down Time?

What Is ACID Property Of A System?

What Is Sticky Session Load Balancing? What Do You Mean By "Session Affinity"?

Explain the purpose of Clean Architecture Inner and Outer layers

What is Back-Pressure?

What is Elasticity (in contrast to Scalability)?

What Do You Mean By High Availability (HA)?

What is the Command and Query Responsibility Segregation (CQRS) Pattern?

What is the difference between the Clean and the N-Tier Architectures?

What is the difference between Behavior-Driven Development (BDD) vs Domain-Driven Design (DDD)?

What does it mean "System Shall Be Resilient"?

What is Bad Design?

Compare Onion vs Clean vs Hexagonal Architectures

What is relationship between Repository and Unit of Work?

What is Unit test, Integration Test, Smoke test, Regression Test and what are the differences between them?

How do you off load work from the Database?

Explain what is Cache Stampede

Compare "Fail Fast" vs "Robust" approaches of building software

What will you choose: Repository Pattern or "smart" business objects?

Is Repository Pattern as same as Active Record Pattern?

How should I be grouping my Repositories when using Repository Pattern?

What is the Dependency Inversion Principle (DIP) and why is it important?

What is GOD class and why should we avoid it?

Two customers add a product to the basket in the same time whose the stock was only one (1). What will you do?

Explain Failure in contrast to Error

Provide Definition Of Location Transparency

What Is Sharding?

Why layering your application is important? Provide some bad layering example.

What's the difference between principles YAGNI and KISS?

Why should you structure your solution by components?

What is BASE property of a system?

Defend the monolithic architecture.

How to handle exceptions in a layered application?

Why should I isolate my domain entities from my presentation layer?

What is actor model in context of a programming language?

What Is IP Address Affinity Technique For Load Balancing?

Explain threads to your grandparents

Are you familiar with The Twelve-Factor App principles?

What does Amdahl's Law mean?

What is the most accepted transaction strategy for microservices?

How do I test a `private` function or a class that has `private` methods, fields or inner classes?