Back-End Interview Questions & Answers


Back-End Interview Questions & Answers

In the ever-evolving realm of technology, the backbone of any digital infrastructure lies in its back end. The back end ensures seamless functionality and data management, from powering web applications to supporting robust databases. Aspiring back-end developers and seasoned professionals often immerse themselves in the intense world of technical interviews, where their skills are tested. Whether you’re an aspiring developer preparing for your first back-end interview or a seasoned professional looking to brush up on your knowledge, this article aims to equip you with a comprehensive guide to common back-end interview questions and their answers.

C# Back-End Developer Interview Questions

  • Describe how synchronous and asynchronous database operations in C# vary.

Asynchronous operations let the execution continue while the operation is in progress, while synchronous operations halt it until it is finished. In back-end applications, asynchronous actions are frequently utilised to increase responsiveness and scalability.

  • What are stored procedures, and how can you execute them in C#?

Stored procedures are precompiled database queries stored on the database server. They can be executed using the SqlCommand object in C#. You pass the name of the stored procedure and any required parameters to the SqlCommand object and then execute it.

  • How do you handle transactions in C# when working with databases?

Transactions in C# can be handled using the System. Transactions namespace. You can create a TransactionScope object and wrap database operations within the scope. The transaction will be rolled back if any operation fails or an exception is thrown.

  • What is the purpose of an ORM (Object-Relational Mapping) framework in C#? Provide an example of an ORM.

An ORM framework like Entity Framework allows developers to work with databases using object-oriented concepts instead of writing raw SQL queries. It maps database tables to classes and provides an abstraction layer for querying and manipulating data. Entity Framework is a popular example of an ORM framework in C#.

  • How can you optimise database queries in C# to improve performance?

Database query optimisation in C# can be achieved by using techniques such as indexing, optimising query structure, avoiding unnecessary joins or subqueries and caching frequently accessed data.

  • Explain the concept of caching in C# back-end development and how it can be implemented.

Caching is the process of storing frequently accessed data in memory to improve application performance. In C#, caching can be implemented using technologies like in-memory caching or distributed caching systems like Redis or Memcached.

  • What is the role of logging in back-end development, and how can you implement logging in C#?

Logging is crucial for monitoring and troubleshooting applications. In C# logging can be implemented using frameworks like log4net, Serilog or the built-in logging capabilities provided by ASP.NET Core. These frameworks allow you to log messages, exceptions and other useful information.

  • How do you secure API endpoints in C# back-end development?

API endpoints can be secured by implementing authentication and authorisation mechanisms. In C# you can use technologies like JWT (JSON Web Tokens), OAuth, or ASP.NET Core Identity to authenticate and authorise users accessing API endpoints.

  • How do you handle concurrency and thread safety in C# back-end applications?

Concurrency and thread safety can be managed in C# by using synchronisation mechanisms like locks, mutexes, or the concurrent collections provided by the System.Collections.Concurrent namespace. Using async/await and the Task Parallel Library (TPL) can also help manage concurrent operations safely.

  • What is the difference between abstract classes and interfaces in C#?

Abstract classes can have abstract and non-abstract methods, while interfaces can only have method signatures. Classes can inherit from only one abstract class but can implement multiple interfaces.

  • Explain the concept of garbage collection in C#.

Garbage collection in C# automatically manages memory by reclaiming objects that are no longer in use. It helps prevent memory leaks and eliminates the need for manual memory management.

  • How do you handle exceptions in C#?

Exceptions in C# can be handled using try-catch blocks. The code that might throw an exception is placed inside the try block, and specific catch blocks are used to handle different types of exceptions that may occur.

  • What is the purpose of the “using” statement in C#?

The “using” statement in C# is used for the automatic disposal of resources. It ensures that resources, such as database connections or file handles, are properly released when they are no longer needed, even if an exception occurs.

  • What are the different access modifiers in C#?

C# provides several access modifiers, including public, private, protected, internal and protected internal. These modifiers control the visibility and accessibility of classes, methods and other members within a program.

PHP Back-End Developer Interview Questions

  • What is PHP, and what are its key features?

PHP is a server-side scripting language used for web development. Its key features include easy HTML integration, database support, extensive library support, and cross-platform compatibility.

  • What are the differences between GET and POST methods in PHP?

The GET method sends data through the URL, while the POST method sends data in the request body. GET is used for retrieving data, while POST is used for sending data and is more secure for sensitive information.

  • Explain the differences between include, require, include_once, and require_once in PHP.

include and require are used to include files but require will cause a fatal error if the file is not found. _once versions prevent multiple inclusions if the file has already been included.

  • What is the difference between sessions and cookies in PHP?

Sessions store data on the server, while cookies store data on the client’s browser. Sessions are more secure and can store larger amounts of data, while cookies have sise limitations.

  • How can you prevent SQL injection attacks in PHP?

To prevent SQL injection, you should use prepared statements or parameterised queries. These techniques ensure that user-supplied data is treated as data rather than executable code.

  • What is the purpose of the “this” keyword in PHP?

This keyword in PHP refers to the current instance of a class. It is used to access class properties and methods within the class itself.

  • How do you handle errors and exceptions in PHP?

Errors can be handled using error handling functions, such as error_reporting and set_error_handler. Exceptions can be caught using try-catch blocks and handled appropriately.

  • What is the difference between abstract classes and interfaces in PHP?

Abstract classes can have method declarations and implementations, while interfaces only declare method signatures. A class can extend only one abstract class but can implement multiple interfaces.

  • How can you secure PHP sessions?

To secure PHP sessions, you should use session_regenerate_id to generate a new session ID on login, set the session cookie parameters with appropriate settings, and store session data securely.

  • What is the purpose of the “autoload” function in PHP?

The “autoload” function in PHP is used to automatically load classes when they are needed, without manually including their files. It helps streamline the process of managing class dependencies.

  • Explain the concept of object-oriented programming (OOP) in PHP.

Object-oriented programming in PHP allows developers to organise code into classes, which encapsulate data and behaviour. It promotes code reusability, modularity and maintainability.

  • What are traits in PHP, and how are they different from classes?

Traits in PHP are a mechanism for code reuse. They allow developers to define sets of methods that can be used in multiple classes. Unlike classes, traits cannot be instantiated directly.

  • How can you handle file uploads in PHP?

PHP file uploads can be handled using the $_FILES superglobal array. You need to specify the form with the enctype attribute set to “multipart/form-data” and use the move_uploaded_file function to move the file to the desired location.

  • How do you work with databases in PHP?

PHP provides several database extensions (e.g., MySQLi, PDO) to connect to and interact with databases. You can establish a connection, execute queries, fetch results, and handle transactions.

  • Explain the difference between GET and POST variables in PHP.

GET variables are passed through the URL and can be seen by the user, while POST variables are sent in the request body and are not visible. GET is used for retrieving data, while POST is used for sending data.

Senior Back-End Engineer Interview Questions

  • What are the key responsibilities of a senior back-end engineer?

As a senior back-end engineer, key responsibilities include designing and developing robust, scalable, and efficient back-end systems, leading technical initiatives, mentoring junior engineers and collaborating with cross-functional teams.

  • Explain the concept of scalability and how it is achieved in back-end systems.

Scalability refers to the ability of a system to handle increasing workloads and growing user demands. In back-end systems, scalability can be achieved through techniques such as horizontal scaling (adding more servers), vertical scaling (upgrading hardware) and implementing distributed architectures.

  • How do you ensure the security of back-end systems and data?

Security in back-end systems involves implementing measures such as data encryption, secure authentication and authorisation mechanisms, input validation and protection against common security vulnerabilities like SQL injection and cross-site scripting (XSS) attacks.

  • Describe your experience with database optimisation and query tuning.

Database optimisation involves improving the performance of database queries and operations. This can be achieved through techniques like indexing, query optimisation, denormalisation, caching and using database monitoring tools to identify bottlenecks.

  • How do you approach designing and implementing RESTful APIs?

Designing and implementing RESTful APIs involves defining clear and consistent API endpoints, using appropriate HTTP methods, adhering to REST principles, handling authentication and authorisation, versioning APIs and providing comprehensive documentation.

  • Describe your experience with message queue systems and their role in back-end architecture.

Message queue systems like RabbitMQ or Apache Kafka facilitate asynchronous communication and decoupling of services in back-end architectures. They help with handling high volumes of requests, enabling scalability, fault tolerance and ensuring reliable message delivery.

  • What is your approach to handling and resolving production incidents and outages?

When faced with production incidents, a senior back-end engineer should be calm, methodical, and have a structured approach to incident response. This involves identifying the root cause, implementing temporary fixes, communicating with stakeholders, conducting post-incident reviews and implementing preventive measures.

  • How do you ensure code quality and maintainability in back-end systems?

Ensuring code quality and maintainability involves practices such as writing clean and modular code, following coding standards, conducting code reviews, writing automated tests, implementing continuous integration and deployment (CI/CD) pipelines and using code analysis tools.

  • Explain the concept of microservices architecture and its benefits.

Microservices architecture is an architectural approach where an application is divided into smaller, loosely coupled services. Each service focuses on a specific business capability and can be developed, deployed, and scaled independently. Benefits include improved scalability, fault isolation, technology flexibility and faster development cycles.

  • How do you handle data consistency and integrity in distributed systems?

In distributed systems, ensuring data consistency and integrity can be challenging. Techniques like distributed transactions, event sourcing, optimistic concurrency control and eventual consistency are commonly used to handle these challenges.

  • Describe your experience with cloud computing platforms (e.g., AWS, Azure, GCP).

Senior back-end engineers should have experience working with cloud computing platforms. This includes deploying applications, setting up scalable infrastructure, configuring load balancers, managing storage and databases, and utilising platform-specific services.

  • How do you approach performance optimisation in back-end systems?

Performance optimisation involves analysing and identifying performance bottlenecks, profiling code, optimising database queries, implementing caching mechanisms, improving network latency and leveraging performance monitoring tools to monitor and improve system performance continuously.

  • What is your experience with containerisation technologies like Docker and orchestration tools like Kubernetes?

Containerisation technologies like Docker provide lightweight, isolated environments for applications, while orchestration tools like Kubernetes help manage containerised applications at scale. Experience with these technologies showcases familiarity with modern deployment practices.

  • How do you ensure the reliability and availability of back-end systems?

Ensuring reliability and availability involves designing for fault tolerance, implementing redundancy and failover mechanisms, monitoring system health and performance, setting up automated alerts and conducting regular load testing and capacity planning.

  • Describe your experience with event-driven architecture and its advantages.

Event-driven architecture focuses on the flow of events and asynchronous communication between components. It allows for loose coupling, scalability, extensibility, and responsiveness in systems that handle high volumes of events or require real-time updates.


In conclusion, this article provided a comprehensive overview of back-end interview questions and answers for both C# and PHP developers. We covered many topics, including database connectivity, caching, logging, API security, concurrency and thread safety.

Aspiring back-end developers can enhance their knowledge and readiness for the interview process by preparing for these interview questions. It is important to note that while the provided answers are brief, they serve as a starting point for further exploration and understanding, and you should practise them well before your back-end interview.

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