Atlassian Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers build and maintain the server-side systems that power web and mobile applications. Day to day, they design APIs, write business logic, manage databases, and ensure services are scalable, secure, and reliable. In global tech companies, they collaborate with frontend, product, and DevOps teams to ship features that serve millions of users.

Role and Technical Knowledge

1. 1

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

   A strong answer covers data structure, scalability, consistency models, and use cases like transactions vs. flexible schemas.

2. 2

   What is a RESTful API? How does it differ from GraphQL?

   Mention statelessness, HTTP methods, resource-based URLs, and GraphQL's single endpoint and client-specified queries.

3. 3

   How does a hash table work? What is its time complexity for common operations?

   Explain hashing, collision resolution (chaining, open addressing), and average O(1) for insert, delete, and lookup.

4. 4

   What is the difference between a process and a thread? How does multithreading help in backend services?

   Cover memory isolation, context switching, shared resources, and concurrency for handling multiple requests.

Practical Scenarios

1. 5

   You need to design a URL shortener like bit.ly. How would you approach it?

   Discuss hashing or base62 encoding, database schema, caching, and handling collisions and scalability.

2. 6

   Your API is experiencing high latency. How would you diagnose and fix it?

   Mention profiling, checking database queries, adding indexes, caching, and load balancing.

3. 7

   How would you handle a situation where a database query is slow due to a missing index?

   Explain using EXPLAIN, adding appropriate indexes, and considering query optimization or denormalization.

4. 8

   Describe how you would implement rate limiting for an API.

   Cover token bucket or sliding window algorithms, using Redis for distributed counters, and returning 429 status.

Behavioural and HR

1. 9

   Tell me about a time you worked in a team to deliver a project. What was your role?

   Use STAR method: describe situation, task, action, and result, highlighting collaboration and impact.

2. 10

   How do you handle tight deadlines or conflicting priorities?

   Show prioritization, communication with stakeholders, and ability to stay calm and focused.

3. 11

   Why do you want to work as a backend engineer at a global tech company?

   Connect personal interest in scalable systems, problem-solving, and desire to learn from large-scale challenges.

4. 12

   Describe a technical challenge you faced and how you overcame it.

   Pick a specific example, explain the problem, your approach, and what you learned.

Advanced Topics and Best Practices

1. 13

   What is the CAP theorem? How does it affect distributed database design?

   Explain consistency, availability, partition tolerance, and trade-offs like CP vs. AP systems.

2. 14

   How do you ensure security in a backend API?

   Cover authentication (JWT, OAuth), authorization, input validation, HTTPS, and protection against SQL injection and XSS.

3. 15

   What are microservices? What are the challenges in moving from a monolith?

   Discuss independent deployment, scalability, but also complexity in networking, data consistency, and monitoring.

4. 16

   Explain how you would write unit tests for a backend service.

   Mention mocking dependencies, testing edge cases, using frameworks like JUnit or pytest, and aiming for high coverage.