Hightouch India Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers at fast-growing global tech companies build and maintain the APIs, services, and data pipelines that power customer-facing products. Day to day, they write server-side code, design database schemas, debug production issues, and collaborate with product and frontend teams to ship features quickly. In smaller or fast-growing firms, they often own services end to end, from design to deployment and monitoring.

Role and technical knowledge

1. 1

   What happens when a user sends a request to a REST API endpoint in a Node.js or Python backend?

   Walk through routing, middleware, business logic, database query, and response serialization. Mention error handling and status codes.

2. 2

   How would you design a database schema for a simple customer data sync tool that stores user profiles and events?

   Cover tables for users, events, and sync jobs with foreign keys and indexes. Discuss normalization versus denormalization for read performance.

3. 3

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

   Focus on schema flexibility, consistency, scaling patterns, and query needs. Give a concrete example like using Postgres for transactions and Redis for caching.

4. 4

   What are idempotent APIs and why do they matter in distributed systems?

   Define idempotency and explain how it prevents duplicate operations on retries. Mention idempotency keys and safe HTTP methods.

Practical scenarios

1. 5

   Your backend service suddenly starts returning 500 errors after a deployment. How do you debug and fix it?

   Check logs and metrics first, then roll back if needed. Describe a systematic process: reproduce, isolate, fix, and add monitoring.

2. 6

   A third-party API your service depends on becomes slow and times out. How do you keep your own service responsive?

   Discuss timeouts, retries with backoff, circuit breakers, and caching. Mention graceful degradation and fallback responses.

3. 7

   You need to add a new feature that requires a database migration on a live production table. How do you approach it safely?

   Cover backward-compatible migrations, adding columns as nullable, backfilling data, and testing on staging. Mention avoiding locks on large tables.

4. 8

   How would you reduce the response time of an API endpoint that is currently taking 2 seconds?

   Profile the endpoint to find bottlenecks. Suggest indexing, query optimization, caching, pagination, or moving work to background jobs.

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 the STAR method. Show curiosity, a structured learning plan, and a concrete outcome like shipping a feature on time.

2. 10

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

   Focus on listening, discussing trade-offs with data, and committing to the team decision. Avoid blaming others.

3. 11

   Why do you want to work at a fast-growing product company like Hightouch India instead of a large established firm?

   Show awareness of the company's product space and eagerness for ownership and impact. Connect your skills to their engineering challenges.

4. 12

   Where do you see yourself in three years as a backend engineer?

   Align your growth with deeper technical expertise and taking ownership of services. Mention mentoring or leading small projects.

Coding and problem solving

1. 13

   Given a list of API request logs, write a function to find the top 3 endpoints with the highest average response time.

   Clarify input format, then use a hash map to aggregate sums and counts. Compute averages and sort or use a heap for top K.

2. 14

   Implement a rate limiter that allows at most N requests per user per minute.

   Discuss sliding window or token bucket. Code a simple in-memory solution and mention Redis for distributed systems.

3. 15

   Write a function to merge two sorted lists of events by timestamp without using extra space beyond the output.

   Use two pointers and compare timestamps. Explain time and space complexity clearly.

4. 16

   How would you detect a cycle in a dependency graph of microservices?

   Model services as nodes and dependencies as directed edges. Use DFS with a recursion stack or topological sort to detect cycles.