Interakt Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers at Indian SaaS and B2B product companies build and maintain the server-side systems that power customer-facing features, APIs, and data pipelines. Day to day, they write code in languages like Node.js, Python, or Java, design database schemas, debug production issues, and collaborate with frontend and product teams to ship features quickly. In fast-growing startups like Interakt, they often own end-to-end modules and work on scaling challenges as the customer base grows.

Role and technical knowledge

1. 1

   What is the difference between SQL and NoSQL databases, and when would you choose one over the other for a SaaS product like a customer communication platform?

   Explain that SQL is good for structured, relational data with ACID guarantees, while NoSQL scales horizontally and handles unstructured data. Give examples like using PostgreSQL for user accounts and MongoDB for chat logs.

2. 2

   How would you design a REST API for a feature that lets businesses send bulk WhatsApp messages to their customers?

   Cover endpoints like POST /messages/bulk, authentication, rate limiting, request validation, and asynchronous processing with a queue to handle large volumes.

3. 3

   Explain how you would implement authentication and authorization in a multi-tenant SaaS application.

   Discuss JWT or session-based auth, role-based access control, and tenant isolation to ensure one customer's data is not accessible to another.

4. 4

   What are database indexes and how do they improve performance? What are the trade-offs?

   Describe how indexes speed up read queries by creating a data structure like B-tree, but slow down writes and take up storage. Mention choosing indexes based on query patterns.

Practical scenarios

1. 5

   A customer reports that their messages are sometimes delayed by several minutes. How would you debug this issue in a backend system?

   Outline steps: check logs for errors, monitor queue lengths, inspect database performance, and review external API rate limits. Suggest adding metrics and alerts.

2. 6

   You need to add a new feature that requires storing additional user data. How would you handle database schema migration in a live production environment?

   Discuss using migration tools, adding nullable columns first, backfilling data, and deploying in phases to avoid downtime. Mention testing on staging.

3. 7

   Your API is getting slow as more customers sign up. What steps would you take to scale it?

   Talk about caching, database read replicas, horizontal scaling with load balancers, and optimizing queries. Also consider asynchronous processing for heavy tasks.

4. 8

   How would you ensure data consistency when a user performs an action that updates multiple tables, such as creating an order and updating inventory?

   Explain transactions with ACID properties, using database transactions or compensating actions in distributed systems. Mention idempotency keys for retries.

Behavioural and situational

1. 9

   Describe a time when you had to learn a new technology quickly for a project. How did you approach it?

   Use STAR method: situation, task, action, result. Highlight self-learning, resourcefulness, and applying knowledge to deliver results.

2. 10

   Tell me about a time you worked in a team to solve a complex problem. What was your role?

   Focus on collaboration, communication, and your specific contribution. Show how you handled disagreements or merged ideas.

3. 11

   Give an example of a bug you encountered in a project. How did you identify and fix it?

   Describe debugging process: reproducing the issue, isolating causes, using tools like logs or debuggers, and testing the fix. Emphasize learning from mistakes.

4. 12

   How do you prioritize tasks when you have multiple deadlines?

   Mention techniques like Eisenhower matrix, communicating with stakeholders, and focusing on impact. Give a concrete example from college projects.

HR and motivation

1. 13

   Why do you want to work as a backend engineer at a fast-growing SaaS company like Interakt?

   Show interest in building scalable systems, solving real-world business problems, and learning in a dynamic environment. Align with company's mission.

2. 14

   Where do you see yourself in the next three years?

   Express desire to grow technically, take ownership of modules, and contribute to architecture decisions. Avoid saying you want to move into management immediately.

3. 15

   What do you know about our company and the products we build?

   Research the company's product, target customers, and recent news. Mention specific features or technologies they use and why they excite you.

4. 16

   How do you handle feedback and criticism?

   Show openness to feedback, give an example of implementing suggestions, and emphasize continuous improvement and learning.