Fortinet | SDE | Backend | Dec 2025 | Offer
Summary
The interview process was challenging but fair, with a strong focus on backend fundamentals, system design, and real project experience. Fortinet interviewers went very deep into discussions, so my key takeaway is that I must know everything written on my resume in depth, as even a single line can lead to detailed follow-up questions. Overall, it was a great learning experience.
Full Experience
Prior experience: ~3years (Product based Company) College: Tier-1 Location: Bangalore Date: Dec 2025
Process: I have taken referral and got call from HR. There were total 5 technical and 1 HR rounds.
Round 1 - Online Assessment (OA)
What was asked:
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One incomplete REST API where I had to implement a missing feature using Java + Spring Boot
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5 SQL questions (queries, joins, basic DB understanding)
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5 CS fundamentals questions (OOPS, basics of OS/DB)
This round tested practical backend understanding, not just theory.
Round 2 - Backend & CS Fundamentals The interviewer started by going through my resume. One line from my resume caught his attention: “ORM optimization”.
From there, he asked many questions one after another to check how well I actually understood backend concepts.
Topics discussed:
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What is ORM and why we use it
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How ORM can be optimized
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Lazy loading vs eager loading
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SQL indexing and joins
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Schema design
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One SQL query
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SQL injection and how ORM helps prevent it
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Other backend security issues
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Kafka basics
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OAuth 2.0 basics
The ORM discussion went very deep, and the idea was to check whether I had real hands-on experience or just theoretical knowledge. I was able to answer most of the questions, but after many follow-ups, I finally gave up 😄.
At the end, there was a coding question. This round was long, intense, and very detailed.
Round 3 - Coding
Problems asked:
- Pascal’s Triangle - https://leetcode.com/problems/pascals-triangle/description/
- Best Time to Buy and Sell Stock II https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/
Round 4 - HLD + Coding
- Coding: Reverse string without extra space The interviewer asked me to explain the architecture of one of my projects that I had worked on.
The discussion went deep into:
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Why I chose this design
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What trade-offs were involved
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What would happen in failure cases
Questions included:
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Writing pseudo-code for a pub-sub consumer
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How async calls were handled
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What happens if:
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- Consumer is down
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- Message queue is down
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How APIs are secured
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How large traffic is controlled
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How CSRF attacks are handled
Learning from this round: You should clearly understand everything you mention in your project. They can easily tell if you’ve really worked on it or not.
Round 5 - System Design
This round was fully focused on design.
Topics discussed:
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Architecture of my master’s project
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OAuth 2.0 in depth
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Discussion on Rate limiter algorithms
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Recovery services
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How services communicate with each other
This was a tight and challenging round.
Round 6 – HR Round
This was a relaxed discussion:
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Why Fortinet?
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What kind of work I’m interested in
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Expectations from the role
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General behavioral questions
Interview Questions (25)
Implement Missing REST API Feature (Java + Spring Boot)
An incomplete REST API was provided where I had to implement a missing feature using Java + Spring Boot.
What is ORM and its Use Cases
Questions on what Object-Relational Mapping (ORM) is and why it is used.
ORM Optimization Techniques
Discussion on various techniques to optimize ORM usage.
Lazy Loading vs Eager Loading in ORM
Detailed discussion comparing lazy loading and eager loading strategies in ORM.
SQL Indexing and Joins Concepts
Questions regarding SQL indexing and different types of joins.
Database Schema Design Principles
Discussion on principles and best practices for database schema design.
SQL Injection Prevention with ORM
Questions about SQL injection vulnerabilities and how ORM frameworks contribute to preventing them.
Kafka Basics
Fundamental concepts and workings of Kafka.
OAuth 2.0 Basics
Fundamental concepts and flow of OAuth 2.0.
Pascal's Triangle
Best Time to Buy and Sell Stock II
You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day, you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However, you can buy it then immediately sell it on the same day. Find the maximum profit you can achieve.
Reverse String In-Place
Implement a function to reverse a string in-place without using extra space.
Pub-Sub Consumer Pseudo-code
Write pseudo-code for a consumer in a publish-subscribe system.
Handling Asynchronous Calls
Discussion on how asynchronous calls were handled in my projects.
Pub-Sub Consumer Downtime Handling
Scenario-based question: What happens if a consumer in a pub-sub system goes down, and how is it handled?
Message Queue Downtime Handling
Scenario-based question: What happens if the message queue itself goes down, and how is it handled?
API Security Mechanisms
Discussion on various mechanisms and best practices for securing APIs.
Handling Large Traffic
Discussion on strategies and techniques for controlling and managing large traffic loads in a system.
CSRF Attack Prevention
Discussion on what CSRF (Cross-Site Request Forgery) attacks are and how they are handled/prevented.
In-depth OAuth 2.0
Detailed discussion on the OAuth 2.0 protocol, including its various flows, components, and security considerations.
Rate Limiter Algorithms
Discussion focused on different algorithms used for implementing rate limiters.
Inter-Service Communication Methods
Discussion on various methods and patterns for communication between different microservices or components in a distributed system.
Why Fortinet?
Behavioral question: Why are you interested in working at Fortinet?
Work Interest
Behavioral question: What kind of work are you interested in performing?
Expectations from the Role
Behavioral question: What are your expectations from this role?