Mar 14, 2023

How to Hire Back-End Developers: 10 Key Questions for a Job Interview

Staff Augmentation


Staff Augmentation, IT Talent, Back-end Developer

Hiring back-end developers can be challenging, especially with the wide range of technologies, tools, and architectures involved. 

When interviewing potential candidates, it's crucial to test their technical knowledge, problem-solving abilities, and alignment with your company's needs. Here are ten essential questions you should consider including in your interview process.

  1.  Explain the Differences Between a Monolithic Architecture and Microservices. 

Understanding the pros and cons of both approaches can indicate the candidate’s familiarity with modern back-end development practices.

-  Expected answer:  A monolithic application is built as a single unit, while microservices break down the application into small services running independently.

  2.  How Do You Ensure Data Integrity in a Database System? 

This will give insight into their understanding of database management and the importance of data integrity.

-  Expected answer:  Regular backups, ACID (Atomicity, Consistency, Isolation, Durability) properties, foreign keys, unique constraints, and database normalization, among others.

  3.  Describe a Time When You Optimized a System's Performance. What Tools and Strategies Did You Use? 

Real-life experiences can reveal their problem-solving skills and familiarity with performance optimization techniques.

-  Expected answer:  The answer can range from database indexing, caching mechanisms, profiling tools, to architectural changes.

  4.  What Are WebSockets, and Why Might They Be Used Instead of HTTP Polling? 

Testing knowledge about real-time communication and the efficiency of different approaches.

-  Expected answer:  WebSockets provide a full-duplex communication channel over a single long-lived connection, reducing the overhead and latency compared to the frequent requests in HTTP polling.

  5.  Can You Explain the Principles of REST? 

Understanding REST is fundamental for web back-end development.

-  Expected answer:  REST stands for Representational State Transfer. Key principles include statelessness, client-server architecture, cacheability, a layered system, uniform interface, and code on demand.

  6.  How Would You Handle Versioning in an API? 

API versioning strategy is vital to ensure backward compatibility and smooth transitions.

-  Expected answer:  Common strategies include URI versioning, request header versioning, and accept header versioning.

  7.  Explain the Concept of "N+1 Query Problem" in ORM (Object-Relational Mapping). How Would You Resolve It? 

This question gauges their understanding of potential pitfalls in ORMs and how to tackle them.

-  Expected answer:  The N+1 query problem occurs when an application executes N additional database queries to fetch the same amount of related data instead of a single query. It can be resolved using eager loading or batch fetching.

  8.  Describe the Differences Between Authentication and Authorization. 

Fundamental concepts in ensuring security in back-end systems.

-  Expected answer:  Authentication is the process of verifying the identity of a user, while authorization determines what an authenticated user is allowed to do.

  9.  How Do You Prioritize Security in Back-End Development? 

Security should be a priority in any development process. This question assesses the candidate's awareness of security best practices.

-  Expected answer:  Secure coding practices, regular code reviews, using security headers, ensuring data encryption, sanitizing user inputs, and staying updated with security patches and vulnerabilities.

  10.  What's the Importance of CI/CD in Back-End Development, and What Tools Have You Used for It? 

Understanding the role of continuous integration and continuous deployment in modern development workflows.

-  Expected answer:  CI/CD improves code quality, accelerates deployment, and promotes frequent code integrations. Tools could include Jenkins, CircleCI, GitLab CI, or Travis CI.

Technical Tests

Technical tests are a critical component of the hiring process for back-end developers, as they provide tangible evidence of a candidate's skills and proficiency. When designing technical tests for back-end developers, it's essential to ensure they reflect real-world scenarios and the specific technologies your company uses. Here are some potential tests you might consider:

1.  Coding Challenges:  

    - Create a RESTful API that performs CRUD operations on a database.

    - Optimize a given slow-performing code snippet or database query.

    - Implement a specific algorithm or data structure (e.g., a sorting algorithm, binary tree traversal).

2.  Debugging Test: 

    - Provide a piece of code with intentional bugs or errors and ask the candidate to identify and fix them.

3.  Architecture and Design: 

    - Present a real-world scenario and ask the candidate to design a system or database schema. 

    - Discuss trade-offs, scalability, and possible optimizations.

4.  Performance Optimization: 

    - Give them a scenario with performance issues (e.g., a slow API endpoint) and ask how they'd investigate and address the problem.

5.  Refactoring Exercise: 

    - Offer a piece of poorly structured code and ask the candidate to refactor it for clarity, efficiency, and maintainability.

6.  Integration Challenge: 

    - Test their ability to integrate with external systems or APIs. For instance, integrate a provided API with a specific database or caching system.

7.  Security Exercise: 

    - Present a piece of code with security vulnerabilities (like SQL injection or exposure of sensitive data) and ask the candidate to identify and rectify them.

8.  Environment Setup: 

    - Ask the candidate to set up a development environment from scratch, potentially using specific tools like Docker, Kubernetes, or CI/CD platforms.

9.  Version Control: 

    - Provide a simulated team scenario using tools like Git. Ask them to resolve merge conflicts, cherry-pick commits, or rebase branches.

10.  Database Challenges: 

    - Design complex SQL queries based on given requirements.

    - Migrate data between different database systems.

    - Optimize database schemas or indexes.

11.  Scenario-based Problem Solving: 

    - Describe a hypothetical situation related to backend development (e.g., a system crash, a specific user complaint) and ask how they would investigate and address the issue.

12.  Live Pair Programming: 

    - Engage in a shared coding session where you can observe their thought process, coding habits, and collaboration skills.

13.  Take-home Projects: 

    - Assign a more extensive project they can complete over a few days, simulating a real-world task. This can also show their commitment and time management skills.

When administering technical tests, it's vital to provide clear instructions, ensure candidates have access to the necessary resources, and set realistic time limits. Additionally, always respect the candidate's time: avoid overly lengthy or complex tests unless they're truly indicative of typical job tasks. Remember, the goal is to understand the candidate's problem-solving skills, coding proficiency, and approach to back-end challenges.

Evaluating Best Practices in Code Implementation

In the realm of technology, the adage that "there's more than one way to skin a cat" often holds true. Multiple solutions can achieve the same outcome, but not all solutions are created equal. Hence, while assessing a programmer's abilities, it is paramount not just to examine the output but the journey they took to get there. Here's why evaluating the standards and best practices a programmer adheres to is vital:

  1.  Code Maintainability:

-  Significance:  Code is written once but read, updated, and maintained numerous times. If a programmer follows industry best practices, it usually means their code is easier to understand and modify by other developers.

-  Evaluation Tip:  Look for clear naming conventions, consistent indentation, and comprehensive comments. 

  2.  Performance Optimization:

-  Significance:  While multiple approaches can solve a problem, some are more efficient than others. Best practices often revolve around optimizing code for speed and resource utilization.

-  Evaluation Tip:  Compare the efficiency of algorithms, check for redundancy, and note the data structures used.

  3.  Security:

-  Significance:  Code that doesn't adhere to best practices can inadvertently introduce vulnerabilities. Secure coding practices protect applications from common threats.

-  Evaluation Tip:  Examine the code for any signs of common vulnerabilities such as SQL injection, cross-site scripting, or insecure data storage.

  4.  Scalability and Future-Proofing:

-  Significance:  In a rapidly evolving tech landscape, code needs to be adaptable to changes. Best practices often incorporate designs that cater to scalability and future expansions.

-  Evaluation Tip:  Check for hard-coded values, tightly coupled components, and the flexibility of the code to handle additional features.

  5.  Collaboration and Team Dynamics:

-  Significance:  In most scenarios, coding is a team effort. Adhering to best practices means that a programmer's code integrates seamlessly with the team's collective output without disruptions.

-  Evaluation Tip:  Examine the code's compatibility with version control, adherence to the project's style guide, and its integration capabilities.

  6.  Resource Management:

-  Significance:  Properly managing resources like memory and system processes is crucial to prevent leaks and ensure smooth application performance.

-  Evaluation Tip:  Look for proper memory allocations and deallocations, and efficient use of system resources.

7.  Testing and Debugging:

-  Significance:  Code that aligns with best practices is typically easier to test and debug. Such code will likely have fewer bugs and better resilience.

-  Evaluation Tip:  Check for unit tests, modular code that can be tested in isolation, and meaningful error handling.


In the intricate tapestry of coding, the path taken often matters as much as the destination. Prioritizing best practices isn't just about meeting a gold standard; it's about ensuring code longevity, security, and collaboration. The nuances in a developer's approach are the silent testament to their caliber and commitment.