Rocketlane Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers in Indian SaaS and B2B product companies build and maintain the server-side systems that power multi-tenant, subscription-based software. Day to day, they write APIs, design database schemas, integrate with third-party services, handle authentication and authorization, and optimise performance for thousands of business users. They work closely with frontend, product, and customer success teams to ship features that solve real customer problems.

Role and technical knowledge

1. 1

   What is multi-tenancy in a SaaS product, and how would you design a database to support it?

   Explain shared vs isolated schemas, tenant ID in every table, and how queries must always filter by tenant to avoid data leaks.

2. 2

   How would you design a REST API for a project management tool like Rocketlane where users can create tasks, assign them, and track status?

   Cover resource naming, HTTP methods, status codes, pagination, and how to handle nested resources like tasks under projects.

3. 3

   Explain the difference between authentication and authorization. How would you implement both in a B2B SaaS app?

   Authentication verifies identity (JWT or session), authorization checks permissions (RBAC or roles). Mention API keys for service-to-service calls.

4. 4

   What are database indexes, and when would you avoid using one in a high-write SaaS application?

   Indexes speed up reads but slow down writes and take space. Avoid on columns with low selectivity or frequent updates.

Practical scenarios

1. 5

   A customer reports that their dashboard loads slowly only during peak hours. How would you debug and fix this?

   Check slow queries, add caching (Redis), optimise indexes, and consider read replicas or queueing background jobs.

2. 6

   You need to send email notifications to users when a task is assigned. How would you implement this without blocking the API response?

   Use a message queue (RabbitMQ, SQS) to process emails asynchronously, with retries and a dead-letter queue for failures.

3. 7

   Your team wants to add a feature that lets customers export all their data as CSV. What are the challenges for a multi-tenant SaaS?

   Handle large data volumes with streaming or background jobs, ensure tenant isolation, and avoid timeouts by paginating or chunking.

4. 8

   How would you handle a situation where a third-party API your product depends on starts returning errors frequently?

   Implement retries with exponential backoff, circuit breakers, fallback responses, and alerting. Log errors for root cause analysis.

Behavioural and HR

1. 9

   Tell me about a time you had to learn a new technology quickly for a project. How did you approach it?

   Use STAR method: describe the situation, the technology, your learning plan, and the outcome. Show curiosity and self-learning.

2. 10

   Why do you want to work in a SaaS product company like Rocketlane instead of a services company?

   Mention interest in building reusable products, solving customer problems at scale, and working in a fast-paced environment with ownership.

3. 11

   Describe a situation where you disagreed with a teammate on a technical decision. How did you resolve it?

   Focus on data-driven discussion, listening, and compromising for the project's benefit. Avoid blaming others.

4. 12

   Where do you see yourself in three years, and how does this backend engineer role fit into that?

   Show ambition to grow into a senior engineer or tech lead, with deeper expertise in system design and mentoring.

Coding and problem solving

1. 13

   Write a function to find the top K most frequent elements in an array. How would you optimise it for a large dataset?

   Use a hash map for counts and a min-heap of size K. For large data, discuss streaming or external sorting.

2. 14

   Given a list of tasks with start and end times, find the minimum number of servers needed to run all tasks concurrently.

   Sort start and end times, use a min-heap to track end times, and count overlapping intervals. This tests interval scheduling.

3. 15

   How would you detect a cycle in a directed graph representing dependencies between microservices?

   Use DFS with recursion stack or Kahn's algorithm for topological sort. Explain time and space complexity.

4. 16

   Write a SQL query to find the top 3 customers by total order value in the last month, given orders and customers tables.

   Use JOIN, WHERE with date filter, GROUP BY customer, SUM order value, ORDER BY DESC, and LIMIT 3. Mention handling NULLs.