10 Web Backend Engineer Interview Questions and Answers for backend engineers

flat art illustration of a backend engineer

1. What inspired you to specialize in web backend engineering?

What inspired me to specialize in web backend engineering was the thrill of solving complex problems that power the backbone of web applications. My passion for coding started at an early age but my real interest in web backend engineering started when I was in college.

  1. I took a class on web development, where I learned the basics of how web applications function.
  2. I was fascinated by the behind-the-scenes work that made websites work seamlessly.
  3. I knew that I wanted to specialize in web backend engineering after my internship where I was assigned to work on an e-commerce platform backend.

During this internship, I learned how to write efficient queries that reduced the load on the database.

  • I contributed to reducing the page load time by 50% using various optimization techniques.
  • I had the opportunity to work on an application that handled more than a million requests per day.
  • My team optimized the application to handle 50% more requests. We upgraded the database architecture, introduced caching strategies and used load balancers to handle requests.

I love that my work as a backend engineer gives me the satisfaction of seeing something complex and powerful come to life. I enjoy every aspect of my job, from designing the algorithm to coding it and deploying it. I believe that the future of the web lies in its backend, and I am excited to be a part of it!

2. Can you walk me through the architecture of a web application you have built?

Sure! For the web application that I built for a previous employer, the architecture was split into three main components: the front-end, back-end, and database. For the front-end, we used React.js to manage the user interface and communicate with the back-end via API calls. This allowed us to easily customize the UI for different user roles and optimize performance by only rendering the necessary components at any given time. On the back-end, we used Node.js and Express.js to handle the API requests from the front-end and interact with the database. We implemented a REST API architecture which provided us with a consistent interface across all entities in the system, since we could simply define CRUD operations for each resource. Finally, the database used was a SQL database, Postgres. We designed our schema such that there was a clear separation between entities and were able to set up efficient indexing strategies to optimize querying speed. Overall, this architecture allowed for a scalable and high-performing web application that met business needs. For instance, user load times decreased by 40%, and the system was able to handle a 25% increase in traffic without any downtime or reduced performance.

3. How do you ensure the security and confidentiality of user data in your applications?

Ensuring the security and confidentiality of user data is a top priority for any web backend engineer. To achieve this, I use a combination of encryption, access control, and regular security audits in my applications.

  1. Encryption: I ensure that any sensitive user data is encrypted both in transit and at rest. Using SSL/TLS encryption for data in transit and AES encryption for data at rest can help prevent any unauthorized access to user data.
  2. Access Control: I maintain strict access controls to user data by implementing authentication and authorization protocols. This restricts access to sensitive data to only authorized personnel who need to access it. Furthermore, Role-Based Access Control (RBAC) ensures that users have access only to the data that they are authorized to access.
  3. Regular Security Audits: Security audits are conducted regularly to ensure that the applications are compliant with security standards such as OWASP Top 10. This helps identify any vulnerabilities, which can be addressed even before they are exploited by malicious actors.

When implementing these measures, I have achieved some significant results in terms of ensuring the security and confidentiality of user data. For instance, in my previous project where I had implemented these measures, there were no data breaches or any form of unauthorized access to user data within the two-year period.

4. Can you tell me about your experience with database management?

Throughout my career as a web backend engineer, I have gained extensive experience with database management. One project that stands out in particular is when I was tasked with optimizing a company's database to improve its performance. After analyzing the current database structure and identifying several performance bottlenecks, I implemented schema changes that significantly reduced the number of queries needed to retrieve data.

  1. To further optimize the database, I also implemented indexing on frequently accessed columns, which resulted in a 60% decrease in query execution times.
  2. On another project, I was responsible for migrating a company's database from a legacy system to a modern cloud-based solution.
  3. I successfully transferred over 100 million records to the new system with no data loss or downtime, resulting in a more efficient and cost-effective solution for the company.

In addition to these projects, I also have experience with creating and maintaining backup and recovery processes, ensuring data security and compliance, and implementing disaster recovery plans in case of data loss.

Overall, my experience with database management has been focused on optimizing performance, ensuring data integrity and security, and implementing effective disaster recovery solutions.

5. How do you handle data migrations while maintaining high availability?

When it comes to handling data migrations while maintaining high availability, my approach involves taking the following steps:

  1. Test the migration in a staging environment: Before performing any data migration, it's crucial to ensure that the migration won't cause any downtime or data loss for our users. I'd first test the migration on a staging environment with a similar setup to our production environment to simulate the possible impacts.
  2. Perform the migration in small batches: Rather than migrating all the data at once, I prefer to take a gradual approach and migrate data in small batches. This helps to minimize the impact on the application's performance and allows us to verify that each batch's migration is successful before moving on to the next batch.
  3. Set up monitoring and alerts: During the migration process, it's important to monitor the application closely to detect any anomalies or failures. I'd set up monitoring tools and alerts that notify the team immediately of any issues that arise during the migration process.
  4. Rollback plan: Despite the careful planning, things don't always go as planned, so I'd have a rollback plan in place. This plan would involve a quick switch back to the old data if anything goes wrong during the migration process, preventing any potential data loss.
  5. Communicate with stakeholders: Finally, I'd communicate the migration process with relevant stakeholders, both internal and external. This helps to set expectations and prepare them for any changes in the application's functionality that may occur during the migration process.

In a recent migration project, we followed these steps, and the results were highly successful. We migrated over 100 million rows of data with minimal impact on our application's uptime and performance. The team was notified quickly of any issues, which enabled us to resolve them promptly. Stakeholders were also kept informed of the migration process, and they praised the efficiency with which we executed the migration.

6. Can you give an example of a particularly challenging bug you faced and how you debugged it?

During my previous position as a Web Backend Engineer at XYZ Company, I faced a particularly challenging bug when the application's server response time increased from a normal 2-3 seconds to over 10 seconds. This issue was causing a negative impact on the user experience, and it was critical that we resolved it as soon as possible.

  1. Firstly, I went through the server logs to try and identify any errors that could be causing the issue. However, after several hours of analyzing the logs, I couldn't find anything significant enough to cause such a significant slow down.
  2. Next, I suspected that the server was experiencing a memory leak since long-running applications can quickly lead to memory exhaustion. I used a tool to monitor the server's memory usage and noticed that it indeed was consistently increasing.
  3. From there, I navigated through the application code line-by-line, starting from the initialization points, to see if there were any memory leaks in any of the scripts. Soon enough, I found out that there was a specific API endpoint that was causing the memory leak.
  4. After running several tests, I discovered that the issue was related to the way the server was handling file uploads that exceeded a certain size. I decided to implement a chunk upload process to handle these bigger files more efficiently.
  5. I then monitored the server response time again and was able to confirm that the problem was fixed. The application response time was back to the normal 2-3 seconds.

As a result of resolving this bug, the customer experience improved significantly, resulting in a 35% increase in usage of the application within the next month.

7. How do you approach testing and scalability in your web backend applications?

Testing and scalability are two crucial aspects of web backend applications. With my experience in web backend engineering, I have developed a structured approach that ensures these aspects are addressed adequately.

  1. Testing: I adopt a comprehensive testing approach that includes unit testing, integration testing, and system testing. This ensures that every component of the application is tested thoroughly before deployment. I use testing frameworks such as Mocha and Chai to write test cases that cover all possible scenarios. I also run load testing to simulate high traffic situations and ensure the application can handle them.
  2. Scalability: To ensure scalability, I design the application with scalability in mind from the outset. This includes using a microservices architecture that allows for independent scalability of different components. I also use cloud services such as AWS Lambda and AWS Elastic Beanstalk, which can efficiently scale up and down depending on traffic demand. With this approach, I have successfully increased the capacity of a web application from handling 100 concurrent users to over 1000 concurrent users while maintaining acceptable response times.

In summary, by adopting a comprehensive testing approach and designing with scalability in mind, I have found that my web backend applications are highly reliable and can handle high traffic demands effectively.

8. Can you explain how you use caching and load balancing to improve application performance?

As a web backend engineer, my focus is always on improving the performance of the application. Two techniques that are essential for achieving optimal performance are caching and load balancing.

  1. Caching: Caching is the process of storing frequently used data in a cache to reduce the amount of time taken to retrieve data. I use caching to store data such as user credentials, frequently accessed APIs, and queries. By caching this data, the load on the server is reduced, and the response time is improved. For example, by caching frequently accessed APIs, I was able to reduce the response time from 500ms to 200ms.
  2. Load Balancing: Load Balancing is the process of distributing network traffic across multiple servers. I use load balancing to optimize resource utilization, increase reliability, and reduce response time. By distributing traffic evenly across servers, load balancing ensures that no server is overburdened, thus improving the application's performance overall. For instance, I was able to reduce the response time of the application from 1 second to 500 millisecond by using load balancing techniques.

Combined, these two techniques can improve the performance of any application. Through my experience, I have found that the use of caching and load balancing can significantly improve the response time of any application. With my expertise, I aim to leverage these techniques to improve the performance of any application that I work on.

9. How do you collaborate with front-end developers and ensure seamless integration?

Collaboration with front-end developers is crucial for ensuring seamless integration of the website or application. I ensure smooth collaboration by following the Agile methodology, which promotes regular communication, collaborative teamwork, and frequent testing.

  1. Firstly, I collaborate with front-end developers by conducting regular standup meetings to discuss project objectives, timelines, and expectations. This allows us to align our efforts and identify potential issues early in the development cycle. We also review code changes and provide feedback to ensure consistency and effective communication.

  2. I utilize modern collaboration tools such as GitHub, Bitbucket or GitLab to manage codebase, track bug reports, and problem-solve through pull requests, branching and merging. This helps in smooth collaboration as there is clear visibility of what each team member is working on and their progress, and it also reduces inefficiencies that arise from working in silos.

  3. To ensure seamless integration, I use automated testing as part of the continuous integration (CI) and continuous delivery (CD) pipeline. With the front-end and back-end developers' collaboration, integration is easier and faster, ensuring smooth user experience.

  4. Moreover, I focus on clean code and follow industry-standard best practices such as RESTful APIs, object-oriented programming(OOP), and secure implementation patterns. This not only helps ensure seamless integration but also promotes maintainability and scalability for future growth.

  5. Finally, I continuously seek feedback from front-end developers and also provide timely feedback to facilitate mutual learning and improvement. I take part in code reviews and pair-programming sessions, which has significantly improved the overall product quality and the effectiveness of the collaboration between the front-end and back-end teams.

By following these steps, I ensure seamless integration with front-end developers leading to successful project delivery.

10. What do you consider to be the most important skills a web backend engineer should possess?

The most important skills a web backend engineer should possess include:

  1. Proficiency in multiple programming languages, such as Python, Java, and C++. This allows for a greater range of flexibility when working on different projects and allows for the engineer to adapt to different team dynamics.
  2. Experience in database management and design, as well as a deep understanding of SQL and NoSQL technologies. Database performance is key to providing fast system responses and minimizing the potential for errors or downtime.
  3. Familiarity with backend frameworks, such as Django or Node.js, and their respective libraries. This provides the engineer with a streamlined development process and allows for faster project completion.
  4. Knowledge of server-side technologies, such as Apache and Nginx. This enables the engineer to effectively deploy web applications and perform server maintenance tasks to ensure satisfactory performance and uptime.
  5. Experience in creating scalable and robust architectures that can handle large amounts of traffic and data. This allows for a more reliable system and reduces the potential for system crashes or data loss.
  6. The ability to work effectively and communicate efficiently with both technical and non-technical team members. This helps to streamline team processes and improves the overall development cycle.
  7. Strong problem-solving skills and the ability to troubleshoot issues quickly and efficiently. This allows for faster bug fixes and reduces the potential for prolonged system downtime.
  8. A thorough understanding of software testing and the ability to write effective unit and integration tests. This ensures that the system is working as intended and reduces the potential for post-release issues or bugs.
  9. Experience in version control systems such as Git. This is essential for effective collaboration and allows for quicker and more efficient code review processes.
  10. Knowledge of security practices and protocols to keep systems, data, and users safe. This helps prevent intrusions, identity theft, and data leaks that can lead to financial and reputational damages.


Congratulations on making it through our list of 10 Web Backend Engineer interview questions and answers! The next step in your job search is to make sure your application stands out with a great cover letter. Check out our guide on

writing a cover letter for backend engineer jobs

to help you get started. Another important part of your application is your resume. Make sure it highlights your skills and experience as a backend engineer by following our guide on

writing a resume for backend engineer jobs

. And if you're on the lookout for remote backend engineer jobs, look no further than our job board at

Remote Rocketship

. We frequently update our board with new and exciting opportunities in the backend engineering field. Good luck in your job search!
Looking for a remote tech job? Search our job board for 30,000+ remote jobs
Search Remote Jobs
Built by Lior Neu-ner. I'd love to hear your feedback — Get in touch via DM or lior@remoterocketship.com