Mastering top backend interview questions and answers: A comprehensive guide


Rachita Jain


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When finding a job, the interview is one of the more critical parts of the process. Backend Developers are in high demand, so preparing for an interview is crucial to success. To help potential job seekers, here are the top backend interview questions and answers.

Backend developer interview questions and answers for beginners

1. What is REST?

One of the most significant questions for freshers during Backend Developer interview questions and answers is- 'What is REST?' The answer to this interview question for Backend Developers is;
REST (Representational State Transfer) is a commonly used backend architecture that provides a stateless communication architecture between distributed systems over the internet. It is an architectural style most widely used for web services and web APIs and is the foundation of many modern technologies.
REST is based on existing web protocols such as HTTP, but its use extends well beyond the web. In REST architecture, resources such as documents, videos, images, entities, or objects in the system are accessible through URLs. Endpoints are URLs a client can use to access these resources.

2. What is SQL?

If you aspire to be a Backend Developer, then this question should be a must in your list of Backend Developer interview questions and answers.
SQL, or Structured Query Language, is a popularly used backend programming language for managing data held in relational database systems. It is used to create, update and delete data from the database. It can also be used to search, retrieve, and organize data from one or more database tables.
SQL is a powerful language used to build custom applications as well as perform ad-hoc data analysis tasks. SQL enables users to create complex web applications such as e-commerce sites and web-based reporting systems.

3. What is SQL injection?

SQL injection is another important backend technical interview question that should be on your list.
SQL Injection is a type of security breach used to attack a backend application by manipulating SQL statements.
  • This type of attack helps to gain access to the underlying data of a website, web application, database, or server. It can be used to gain access to confidential data, modify existing data and even delete it.
  • SQL injection is considered the top source of web application security vulnerabilities. Malicious people often use it to gain access to a backend database or to modify or delete the data held within it.
  • The malicious user might be able to steal sensitive information. Then he can perform malicious actions on the system without any authentication or authorization.

4. What are the different programming languages you prefer?

This is the most common Backend Developer interview questions, and answers asked from freshers. Using this Backend Developer interview question, the interviewer is trying to get hold of your skills and abilities. Make sure you answer this technical backend interview question quite sincerely.
Regarding backend programming languages, some of the most popular choices are Python, PHP, Java, and NodeJs.
  • Python is famous for its readability and reliability.
  • PHP is powerful for web development.
  • Java is a versatile language suitable for developing mobile and enterprise applications.
  • NodeJs is also famous for building backend applications due to its asynchronous programming abilities.

5. Explain the concept of HTTP and HTTPS.

The use of HTTP (Hypertext Transfer Protocol) is for transferring data over the web. Hypertext Transfer Protocol Secure, i.e. HTTPS, is a secure version of HTTP. HTTPS uses encryption to protect data during transmission.

6. What are the benefits of web series?

Given its significance, a web series becomes a pivotal topic, making it one of the foremost inquiries in backend technical interviews.
  • Reusability: Multiple client programs may utilize a single web service simultaneously.
  • Interoperability: Web services may be accessible over the network thanks to interoperability. It operates on the HTTP/Soap protocol and transports data using XML/JSON. Any programming language may be used to create it.
  • Easy to install and integrate: Web services can be deployed and integrated quickly and simply.
  • Numerous service versions: Several service versions may be active all at once.
  • Loose coupling: Web services have a loose coupling since the client and server code are independent.

7. What is the CAP theorem?

CAP theorem is another crucial Backend Developer interview question and answer for freshers that you can be asked during your Backend Developer interview.
The CAP theorem, also known as Brewer's theorem, is a popular concept in the field of distributed systems. The CAP theorem states that it is impossible for a distributed system to exhibit all three of the following properties simultaneously:
  • Consistency: It implies that every read receives the most recent write or an error
  • Availability: Every request receives a response - without the assurance that it contains the most recent write
  • Partition tolerance: It implies that the system continues to operate despite an arbitrary network partitioning between nodes
The CAP theorem says that in a distributed system, it is impossible to guarantee all three of the above characteristics simultaneously. Instead, the system must make a trade-off between two of the three.

8. What is spike testing?

Spike testing is non-functional testing that focuses on testing the performance of backend systems under increased loads or surges in traffic. It involves testing the system with more requests, higher concurrent users, or larger data volumes to observe how it responds to sudden short-term spikes in resource usage. Spike testing is typically part of a larger performance testing plan and provides valuable insight into how a system can handle real-world scenarios.

9. Describe the process of debugging.

Regarding debugging in the backend, the process can involve several different techniques. This process aims to identify bugs in the backend code or system that could cause unexpected problems for users. Depending on the complexity of the system, debugging may involve a combination of testing, debugging methods, and problem-solving techniques.
  • Testing is the first step in debugging in the backend. This can involve unit and integration testing, as well as integration and performance testing.
  • After testing, developers can use various debugging methods to locate and fix errors.
  • Next, developers can use breakpoints and debuggers to go through the code line-by-line.
  • Finally, the last step in the debugging process is problem-solving.

10. What are NoSQL databases?

If you are a fresher applying for the job of a Backend Developer, then this Backend Developer interview question and answer is a must in your list.
NoSQL databases, often referred to as "not only SQL" databases, are a class of database management systems that provide a non-relational approach to data storage and retrieval. Unlike traditional relational databases (SQL databases), which use structured tables with predefined schemas, NoSQL databases offer more flexibility and scalability for handling large volumes of unstructured or semi-structured data.

Backend developer interview questions and answers for senior Backend Developers

11. What are local variables and global variables?

One of the most critical backend technical interview questions and answers for senior Backend Developers is the difference between local and global variables.
Python is an object-oriented programming language. It has become increasingly popular recently. As with any programming language, there are two types of variables: local and global variables.
Local variables
Global variables
Local variables are those that are declared within a function or class.
Global variables, on the other hand, are accessible throughout the entire program.
They are only accessible within the scope of the function or class and are not available outside of it.
They are declared outside any function or class and accessible from any part of the program.
Local variables often store intermediate results and data that only need to be used within the function or class.
Global variables are often used when a program needs to access the same data from different parts of the program.

12. Differentiate between Python arrays and lists?

Python Arrays and Lists are data structures that store values or data. They both have similar operations associated with them but also have distinct differences.
  • Arrays are best suited for storing homogeneous data, meaning data of the same type. This makes it easier to iterate through data elements in an array. Arrays are typically fixed-length, meaning they cannot be dynamically modified or resized. This limits the kinds of elements that can be stored in an array.
  • Lists are similar to Arrays but are more versatile. Unlike Arrays, Lists can store heterogeneous data, meaning data can come from different types. This allows for greater flexibility in the kinds of values that can be stored. Lists are also dynamic, meaning they can be resized or modified anytime.

13. What are the various types of Arrays in PHP?

As an experienced senior Backend Developer, it's essential to have a thorough understanding of the following interview questions tailored for your role:
Indexed array: The most basic array type is the indexed array, simply an array of values. Values are stored in the array using numbers as keys, starting from 0 and incrementing for each item. This is an excellent solution for storing information like the list of names, phone numbers, or even employee numbers.
Associative array: A second type of array is the associative array. This type of array uses strings as keys; the values can be anything from another array to an integer or string. Associative arrays can be used to store information such as name-value pairs in a database or key-value pairs in a search result.
Multidimensional array: This type of array allows you to store multiple levels of data, such as a collection of different value pairs under a single key. This can be used to store complex data, such as a hierarchy of categorical information or a 3D object in a scene.
Hybrid array: Hybrid array combines elements from all the other types of arrays. This is useful if you need to store a list of associative values, numbers, and items in an array. Hybrid arrays are especially useful when dealing with deeply nested structures, such as when dealing with a complex database structure or an organizational chart.

14. What is NULL in the backend?

NULL is a special value in backend programming that represents empty or missing data. It is distinct from zero, a valid value, and from the empty string, another valid value. NULL is different because it behaves differently than other values and often must be handled differently in terms of programming.
NULL is used in databases to indicate missing data. The database record may be incomplete, or the value may be unknown. NULL can also be used in coding to indicate that something is undefined or an error has occurred. It can also be used as a placeholder for an unknown value as a programming shortcut.

15. How to define a constant in PHP?

A constant in a PHP is an inescapable interview question for Backend Developers.
To define a constant in PHP, you simply need to use the define() function. This define() function takes two arguments - the first is the constant name, and the second is the value.
For example:
define('CONSTANT_NAME', 'This is a constant);
By default, constants are global and can be accessed throughout your program.

16. What is unpickling and pickling?

Pickling and unpickling are two processes used in the computer programming language Python.
Pickling converts a Python object hierarchy (a set of objects and their associated data) into a byte stream.
Unpickling is the reverse process, converting the byte stream into a Python object hierarchy.

17. What is a trigger in SQL?

Trigger SQL is one of those backend technical interview questions and answers that every senior Backend Developer should be familiar with.
A trigger in SQL is a piece of code that is stored in the SQL server and executed automatically whenever a particular database operation occurs. Triggers are most commonly used to maintain the integrity of the data in a database, applying data-level rules that check input and updated records. They are typically used to apply auditing or logging rules, data corrections or updates, or record updates in related tables.
Trigger code is usually written in the Structured Query Language (SQL). In most databases, a trigger can be set up to run on specified events like either changes to or retrieving data from specific tables. When activated, a trigger is executed as part of the statement that caused it to be encountered. Triggers can be used to apply the same transformation, data-level validation, and validation rules across an entire data set.

18. Explain the reverse proxy concept and how it can improve backend performance and security.

A reverse proxy is like an intermediary between clients and servers, handling tasks like load balancing, caching, SSL termination, and protecting backend servers from direct exposure to the internet. It enhances performance by serving cached content and improves security by masking backend server details.

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