Druva Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers in Indian SaaS and B2B product companies build and maintain server-side systems that power multi-tenant, cloud-native applications. They design APIs, work with databases, ensure scalability and security, and collaborate with frontend, DevOps, and product teams. Day to day involves writing code, reviewing pull requests, debugging production issues, and optimising performance for enterprise customers.

Role and technical knowledge

1. 1

   How would you design a REST API for a SaaS product that manages user data for multiple tenants?

   A strong answer covers tenant isolation (e.g., tenant ID in requests), authentication, rate limiting, and versioning. Mention database partitioning or schema separation for multi-tenancy.

2. 2

   Explain the difference between SQL and NoSQL databases. When would you choose one over the other for a B2B SaaS backend?

   Discuss consistency, scalability, and data structure. For B2B SaaS, SQL is often preferred for transactional data, while NoSQL may suit high-volume logs or unstructured data.

3. 3

   What are the key considerations for making a backend service scalable in a cloud environment?

   Cover horizontal scaling, load balancing, caching, asynchronous processing, and database sharding. Mention cloud services like auto-scaling groups and managed databases.

4. 4

   How do you ensure security in a multi-tenant SaaS application?

   Focus on authentication, authorization, data encryption, input validation, and regular audits. Mention tenant isolation and role-based access control.

Practical scenarios

1. 5

   You notice a sudden spike in API latency for a key endpoint. How would you debug and resolve it?

   Describe a systematic approach: check logs, monitor metrics, profile database queries, and review recent deployments. Suggest caching or query optimisation if needed.

2. 6

   A customer reports that their data is missing from the dashboard. How would you investigate?

   Outline steps like checking data pipelines, verifying tenant ID filtering, reviewing recent code changes, and testing with sample data. Emphasise communication with the customer.

3. 7

   You need to add a new feature that requires changes to the database schema without downtime. How would you approach it?

   Discuss backward-compatible migrations, using tools like Flyway or Liquibase, and phased rollouts. Mention testing in staging and rollback plans.

4. 8

   How would you handle a situation where your code passes tests locally but fails in production?

   Highlight differences in environment, configuration, and data. Suggest using containerisation, infrastructure as code, and comprehensive logging to diagnose issues.

Behavioural and HR

1. 9

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

   Use the STAR method. Focus on collaboration, your specific contribution, and the outcome. Show willingness to learn and adapt.

2. 10

   Why do you want to work as a backend engineer in a SaaS company like ours?

   Show interest in cloud technologies, multi-tenant architectures, and solving enterprise-scale problems. Mention the company's product or tech stack to demonstrate research.

3. 11

   Describe a situation where you had to learn a new technology quickly. How did you go about it?

   Emphasise self-learning, resourcefulness, and application of the new skill. Provide a concrete example, such as a project or hackathon.

4. 12

   Where do you see yourself in the next two years?

   Align your growth with the company's needs, such as deepening backend expertise, taking ownership of modules, and contributing to system design.

Advanced backend and SaaS concepts

1. 13

   How would you implement rate limiting for APIs in a multi-tenant environment?

   Discuss algorithms like token bucket or leaky bucket, and per-tenant limits. Mention using Redis or API gateways for distributed rate limiting.

2. 14

   What is idempotency and why is it important in backend APIs?

   Explain that idempotent operations produce the same result if called multiple times. Give examples like payment processing and how to implement idempotency keys.

3. 15

   Explain how you would design a notification service that sends emails and SMS to users of a SaaS product.

   Cover message queues, third-party integrations (e.g., SendGrid, Twilio), retry mechanisms, and user preferences. Mention scalability and fault tolerance.

4. 16

   What are the trade-offs between monolithic and microservices architectures for a B2B SaaS product?

   Discuss development speed, scalability, complexity, and team structure. For a growing SaaS, microservices can offer flexibility but require DevOps maturity.