16 Real Interview Questions for Backend Software Engineers
If you’re preparing for a backend software engineering interview, you’ll want to master both the theory and the practical side of core concepts. Here are 16 real interview questions, with clear explanations to help you get ready for your next big opportunity.
1. What makes an API RESTful? What is an example of a non-RESTful API?
A RESTful API (Representational State Transfer) is built around resource-oriented architecture principles and organized using HTTP verbs like GET, POST, PUT, and DELETE. It typically uses JSON or XML for data exchange and relies on HTTP status codes to communicate results. Examples of non-RESTful APIs include SOAP, gRPC, and GraphQL.
2. What is content negotiation? Provide an example.
Content negotiation is an HTTP feature that allows a web server and browser to agree on the format of data exchanged, such as JSON, XML, or compressed formats. This is managed through headers like Accept, Accept-Language, and Accept-Charset.
3. Compare and contrast SQL and NoSQL databases.
SQL databases provide ACID compliance and use a fixed data schema, making them ideal for applications that require data consistency and integrity. NoSQL databases, on the other hand, store data in formats like documents, graphs, or key/value pairs. They excel in scenarios where speed, scale, or flexible schemas are needed.
4. Provide a use-case for SQL databases.
SQL databases are well-suited for applications that prioritize data consistency, accuracy, and integrity—such as financial systems, complex queries, and any scenario where data integrity is critical.
5. Provide a use-case for NoSQL databases.
NoSQL databases are a great fit for content management systems (CMS), product catalogs, and distributed systems where the data structure can change frequently or needs to scale horizontally.
6. In reference to SQL databases, what is the ACID acronym?
ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that database transactions are reliable and maintain data validity even in the event of errors or failures.
7. Compare and contrast GraphQL and REST.
Both GraphQL and REST are used for data exchange between clients and servers. REST organizes endpoints around resources (like GET /users/123), which can sometimes lead to over-fetching or under-fetching of data. GraphQL uses a single endpoint, allowing clients to request exactly the data they need, making it more flexible and efficient in many cases.
8. What are advantages and disadvantages to using GraphQL?
GraphQL offers flexibility and efficiency by letting clients specify exactly what data they need. However, it can introduce complexity on the server side and may require more careful management of queries and performance.
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9. What are advantages and disadvantages to using REST?
REST is simple, widely adopted, and leverages standard HTTP protocols. Its resource-based structure is easy to understand, but it can be less efficient for complex data needs, sometimes requiring multiple requests to gather related data.
10. What is the N+1 problem?
The N+1 problem occurs in Object-Relational Mappers (ORMs) when one database call returns N objects, and then N additional calls are made to fetch related data. This can lead to performance issues if not managed properly.
11. What are SOLID design principles?
SOLID is a set of principles aimed at improving object-oriented software design:
- Single Responsibility
- Open/Closed
- Liskov Substitution
- Interface Segregation
- Dependency Inversion
12. What are design patterns? Name some of the design patterns you’re familiar with.
Design patterns are standard, reusable solutions to common problems in software development. Examples include creational patterns like builder, factory, and singleton; structural patterns like adapter, decorator, and facade; and behavioral patterns like observer, strategy, and command.
13. What is a monolith / monolithic application?
A monolithic application is a single, unified program where all components are tightly coupled. It typically has a single codebase, tech stack, and deployable unit. Monoliths are simpler to design and deploy initially, but can become harder to scale and maintain as complexity grows.
14. What are microservices?
Microservices architecture structures an application as a collection of small, independent services modeled around business domains. These services are modular, decentralized, and can be developed, deployed, and scaled independently.
15. What are advantages and disadvantages of using microservices?
Microservices offer scalability, flexibility, resilience, and easier deployment. However, they introduce complexity, challenges with data consistency, and additional overhead in development and testing.
16. What should you look for to know when it’s appropriate to split to microservices?
Consider splitting to microservices when you face difficulty scaling individual services, reduced development velocity, deployment downtime, differing reliability requirements, diverse technology needs, or the need for continuous delivery.
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