10 GraphQL API design Interview Questions and Answers for api engineers

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1. What do you consider to be the benefits of using GraphQL over REST?

GraphQL provides several benefits over REST:

  1. Reduced data transfer: GraphQL allows you to retrieve only the data you need, reducing network traffic and improving performance. According to a study by Diaspora, GraphQL can reduce data transfer by up to 70%, resulting in faster response times and improved user experience.
  2. Better client-server communication: With REST, clients have to make multiple requests to retrieve related data. This can lead to overfetching (retrieving more data than necessary) or underfetching (not retrieving enough data). GraphQL solves this problem by allowing clients to specify their data requirements in a single query, which the server can then fulfill with a single response.
  3. Schema-based development: GraphQL uses a strongly-typed schema to define the data model and operations, which helps to prevent errors and improves development speed. The schema also serves as documentation for the API, making it easier for developers to understand and use.
  4. Better developer experience: The ability to retrieve only the data you need and the schema-based development model both contribute to a better developer experience. In addition, tools like GraphQL Playground and GraphiQL make it easy to explore and test GraphQL APIs.
  5. Flexibility: GraphQL's ability to retrieve related data in a single query can make it more flexible than REST. For example, you can easily retrieve a list of users and their posts in a single query without having to make multiple API requests.

2. What experience do you have in designing and implementing GraphQL APIs in a production environment?

I have extensive experience in designing and implementing GraphQL APIs in a production environment. In my previous role as a Senior Backend Developer at XYZ Company, I was responsible for leading the development of a GraphQL API for a mobile application used by over 1 million users.

To ensure the API was scalable and efficient, I implemented advanced caching techniques that reduced response times by over 50%. Additionally, I integrated Apollo Federation to enable microservices to own their own data and expose it through a unified GraphQL API, resulting in a more flexible and maintainable architecture.

Through thorough load testing and monitoring, I identified bottlenecks and optimized the API to handle up to 10,000 concurrent requests with no significant performance degradation. As a result, we were able to increase user engagement and reduce API downtime by 90%.

I also implemented robust security measures, including rate limiting, authentication, and authorization, to ensure the API was protected against potential attacks. In doing so, the API passed rigorous security audits and received high-security ratings from independent third-party testers.

Overall, my experience designing and implementing GraphQL APIs in a production environment has demonstrated my ability to deliver high-performance, scalable, and secure APIs that meet the needs of complex applications and large user bases.

3. Tell us about a time when you had to troubleshoot a performance issue with a GraphQL API. How did you go about resolving it?

During a project in 2022, I was responsible for implementing a GraphQL API that would be used by a large number of clients. However, after a few days of deployment, we started noticing some performance issues with the API. There were delays in the response time which meant that the API was not functioning optimally.

As soon as I realized that there was a problem, I started investigating the issue by looking at the logs and analyzing the queries that were being executed. I noticed that some of the queries were taking longer to execute than others. Through further analysis, I discovered that there were some N+1 query problems causing the performance issues.

To resolve the problem, I optimized the queries to reduce the number of database calls. I also used caching to decrease the time taken to load the data. Additionally, I made sure that the database was properly indexed to increase query execution efficiency.

After implementing these changes, I ran a series of tests to ensure that everything was working correctly. The results were significant- the API was running much faster than before. The response time had reduced by over 50%, and clients were able to access data much more quickly.

Overall, this experience taught me the importance of regular testing and continuous optimization of the API to guarantee that it is functioning optimally.

4. What tools and libraries do you use when designing and implementing GraphQL APIs?

When designing and implementing GraphQL APIs, I have experience using a variety of tools and libraries. Here are a few of the key ones I frequently use:

  1. GraphQL Nexus: This is a great tool for rapidly developing GraphQL APIs. It helps automate a lot of the boilerplate code and makes it easy to define the schema.
  2. Apollo Server: This library simplifies the setup process for creating a GraphQL server. It also provides useful features such as caching and error handling.
  3. Prisma ORM: This tool makes it easy to interact with databases in a GraphQL context. Its type-safe API helps avoid common errors and allows for easy database migrations.

Using these tools and libraries has led to some tangible benefits for the projects I have worked on. For example:

  • One project saw a 30% decrease in the time it took to develop the backend API thanks to using GraphQL Nexus and Apollo Server.
  • Another project that used Prisma ORM saw a reduction in database query time of around 50%, due to the type-safe API helping us catch and fix inefficient queries early on in development.

Overall, I believe that using the right tools and libraries when designing and implementing GraphQL APIs can greatly improve the development process and deliver better results for end users.

5. How do you ensure that security concerns are addressed when designing and implementing GraphQL APIs?

When designing and implementing GraphQL APIs, it is crucial to address security concerns to protect our data and ensure the privacy of our users. To achieve this, we can take several measures:

  1. Authentication and Authorization: We can implement various authentication and authorization techniques such as OAuth 2.0, JWT, or API keys to ensure that only authorized users can access the data. This will prevent unauthorized access to sensitive information.
  2. Data validation and sanitization: We can validate and sanitize the user inputs to prevent SQL injection, XSS, and other security vulnerabilities. We can use input validation libraries such as Joi or Yup to handle the validation and sanitization logic.
  3. Rate limiting and throttling: We can implement rate limiting and throttling techniques to prevent DDoS attacks and brute force attacks. This will restrict the number of requests that can be made within a certain timeframe and prevent overload.
  4. Encryption: We can secure the transmission of data with SSL/TLS encryption to prevent man-in-the-middle attacks. This will ensure that the data is not intercepted and tampered with during transmission.
  5. Logging and monitoring: We can implement logging and monitoring mechanisms to keep track of the API activity and detect any unusual behavior. This will help us identify security threats and take appropriate actions.

At my previous job, we followed these security measures while designing and implementing the GraphQL APIs. The result was that we were able to provide a secure and reliable API to our users. We did not face any security breaches or attacks, and our users' data was safe and confidential.

6. How do you approach versioning and backwards compatibility with GraphQL APIs?

Versioning and backwards compatibility are crucial aspects of designing GraphQL APIs. My approach is to design APIs that are backwards compatible, meaning that new changes should not break existing functionality.

  1. Breaking changes: Before making any updates or changes, I categorize them into three categories:
    • Major Changes: Changes that will require clients to update their code and can potentially break their existing codebase.
    • Minor Changes: Changes that will not break client code, but will add new features.
    • Patch Changes: Changes that are backward compatible and do not require any client changes.
  2. Versioning: Once changes have been categorized, the next step is versioning the GraphQL schema.
    • Major Version: Any breaking changes will require a major version increase (e.g., v1 to v2).
    • Minor Version: Non-breaking changes will result in a minor version increase (e.g., v1 to v1.1).
    • Patch Version: Patch changes will not result in version number changes (e.g., v1.0 to v1.0).
  3. Deprecated Fields: In order to maintain backward compatibility, I make use of the "deprecated" directive in the schema to indicate when a field is being phased out.
    • The directive allows clients to continue using the deprecated field, but with a warning that it will eventually be removed.
    • Deprecated fields can still be accessed until they are removed entirely, ensuring compatibility with existing clients.
  4. API versioning in the URL: I include the API version in the URL so that clients can request specific versions of the API.
    • This eliminates the need for clients to update their code each time there is a breaking change, as they can choose to continue using old versions of the API.
  5. Testing: Before deploying any changes, I thoroughly test the API to ensure that it is backward-compatible and will not break existing functionality.
    • I test both the new and old versions of the API to ensure that they work seamlessly together.
    • Testing includes integration testing, unit testing and performance testing.

Using this approach, I have been able to maintain backward compatibility with existing clients, while still implementing new features and making non-breaking changes to the GraphQL APIs. As a result, clients have been able to transition to new versions of the APIs seamlessly and without any issues.

7. What strategies do you use to optimize data fetching and minimize round-trips in a GraphQL query?

When optimizing data fetching in a GraphQL query, my approach is to:

  1. Reduce the number of queries: By combining multiple queries into a single query, we can minimize the number of round-trips, thus optimizing data fetching. To achieve this, I implement batching, which allows us to group multiple queries into a single request.
  2. Prioritize the most important data: When it comes to data fetching and optimization, not all data is equal. So, I prioritize the data that is most critical to the application and user experience. This could include the data that is displayed on the initial page load or the main data that the application relies on to complete important tasks.
  3. Use caching: With caching, we can reduce the number of round-trips by storing frequently accessed data and fetching it from the cache instead of the server. This can significantly improve performance and reduce unnecessary queries. I make use of libraries like Facebook's DataLoader to handle caching.
  4. Explore pagination: When dealing with large data sets, pagination helps us reduce the amount of data fetched at once. This way, we can fetch just the required data to display and load more data as needed. I use Relay's pagination techniques to implement this.
  5. Reduce the size of the response: Large query responses can be a bottleneck for application performance. To minimize the size of the response, I restrict the fields requested and implement field-level resolution to retrieve only required fields. This way, unnecessary data is not included in the response.

Together, these strategies can significantly optimize data fetching and minimize round-trips in a GraphQL query.

8. How would you structure the schema for a complex GraphQL API that involves multiple data sources?

Here's a possible answer to the job interview question "How would you structure the schema for a complex GraphQL API that involves multiple data sources?":

When designing a GraphQL schema for a complex API that involves multiple data sources, I would follow these steps:

  1. Identify the entities and relationships that are relevant to the API's use case. For example, if the API is for a social network, I would consider users, posts, comments, likes, and their associations.
  2. Group the entities and relationships into logical modules that correspond to the different data sources. For example, users and their profiles might come from a SQL database, posts and comments might be stored in a document database, and likes might be cached in a NoSQL store.
  3. Create types in the GraphQL schema that correspond to each module, and define their fields and relationships. For example, a User type might have fields like id, name, email, and posts, where posts is a collection of Post types that belong to the user.
  4. Implement resolvers that fetch the data from the appropriate data sources and return it in the form expected by the GraphQL schema. For example, a resolver for the posts field of the User type might fetch the posts from the document database and transform them into an array of Post objects.
  5. Compose the individual modules into a cohesive schema that reflects the overall API functionality. For example, I could define queries that return users by criteria, posts by user, comments by post, and so on.

By structuring the schema in this way, I would be able to achieve several benefits:

  • Each module would be responsible for its own data, reducing the complexity and coupling of the overall system.
  • Each module could be scaled and optimized independently, improving the performance and throughput of the API.
  • The schema would provide a clear and intuitive interface for clients to interact with, reducing the learning curve and maintenance costs.

Ultimately, the success of a GraphQL API depends on its ability to provide flexibility, performance, and ease of use to clients. By following a modular and pragmatic approach to schema design, I would be able to achieve these goals and deliver a high-quality API.

9. How do you approach testing and validation when working with GraphQL APIs?

When it comes to testing and validation for GraphQL APIs, my approach involves several steps:

  1. Documenting API expectations: Before building any tests, I make sure to understand the expected behavior of the API, as well as any potential edge cases or unexpected outcomes. This allows for more targeted testing later on.
  2. Integration testing: Using a tool like Apollo or GraphiQL, I perform integration testing to ensure that the queries and mutations are functioning as expected, with all necessary data and fields accurately returned.
  3. Unit testing: To test individual functions or resolvers, I use tools like Jest or Mocha. This helps catch any errors or issues at the code level before they become larger problems.
  4. Validation: Data validation is an important step to ensure that all data is accurate, consistent, and adheres to the defined schema. I use a combination of libraries like Yup and Joi, as well as manual inspection, to validate incoming and outgoing data.
  5. Load testing: Finally, to test the scalability and performance of the API, I use tools like k6 or Artillery to simulate heavy loads and check for any issues or bottlenecks in the system.

Overall, by combining a variety of testing approaches, I can ensure that the GraphQL API is functioning as expected, with accurate data and strong performance. In my previous project, I was able to catch and resolve several critical bugs before deploying to production, resulting in a smoother experience for end-users and a more reliable system overall.

10. What have been some of the biggest challenges you've faced when designing and implementing GraphQL APIs?

When designing and implementing GraphQL APIs, I have faced a few significant challenges. One of the most significant challenges was optimizing query performance for larger datasets. To address this issue, I implemented data caching and pagination. By caching frequently accessed data, we were able to significantly reduce query time and improve overall performance. Additionally, pagination helped to reduce the amount of data retrieved in each individual query, further improving performance.

Another major challenge we faced was managing complex data relationships. To solve this issue, we implemented a data modeling strategy that allowed us to break down complex relationships into smaller, more manageable data types. This approach helped us to maintain flexibility and scalability as we continued to expand our API.

We also faced issues with query complexity and security. In response, we implemented a security strategy that included user authentication and authorization, rate-limiting, and query whitelisting. This helped to ensure that only authorized users were able to access sensitive data and helped to prevent overloading the API with unnecessary queries.

Overall, while there were a number of challenges in designing and implementing GraphQL APIs, we were able to overcome these obstacles through careful planning and proactive problem solving. As a result, our API was able to deliver high-quality data and excellent performance to our users.


Congratulations on taking the time to prepare for your GraphQL API design interview! Now that you have aced these common questions, it's time to take the next steps towards landing your dream job as a remote API engineer. One of the first things you should do is craft an outstanding cover letter that showcases your skills and experience. Our guide on writing a cover letter for API engineers can help you get started. Don't underestimate the power of a well-written cover letter, as it can be the key to getting your foot in the door. Another crucial element is having a strong resume that highlights your past achievements and qualifications. Check out our guide on writing a resume for API engineers to ensure that your CV stands out from the crowd. And finally, don't forget to utilize Remote Rocketship's job board for remote API engineer jobs. With new opportunities added daily, you never know when your dream job may pop up. Check out our job board today to start your job search journey!

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