Demonstrate clear knowledge of the backend developer position, including core responsibilities and the technology choices that commonly support them. Topics include designing application programming interfaces, service and data models, database design and query optimization, authentication and authorization strategies, scalability and performance trade offs, reliability and observability practices, security considerations, test strategies for backend code, deployment pipelines and release workflows, and familiarity with common runtime platforms and infrastructure such as Node.js, Python, Java, PostgreSQL, MongoDB, Amazon Web Services, and Microsoft Azure. Candidates should also be able to ask targeted questions about existing architecture, integration points, expected throughput and latency, operational responsibilities, and the team ownership model.
MediumTechnical
56 practiced
Design a caching strategy for a product catalog service with heavy reads and infrequent writes. Compare cache-aside, write-through, and write-back policies. Recommend a strategy considering cache invalidation, TTL, stale reads, and cold starts. Also describe how you'd use Redis (clustering, persistence settings) in production and how to mitigate cache stampede.
MediumTechnical
58 practiced
Explain optimistic vs pessimistic locking and when to use each. Then provide code (in Java or Python) demonstrating optimistic locking for updating product inventory using a 'version' integer column: read the row, check the version, update where id and version match, and handle retry on conflict. Specify transaction boundaries and backoff strategy for retries.
MediumTechnical
81 practiced
You're deploying a schema migration that adds a NOT NULL column with a default to a very large production PostgreSQL table. Describe a zero-downtime migration plan that avoids long locks: include steps such as adding a nullable column, backfilling in batches, deploying code tolerant to nulls, switching to NOT NULL with a constraint, and rolling back if necessary. Mention monitoring, potential pitfalls, and rollback considerations.
HardSystem Design
59 practiced
Design a multi-region deployment for a social app that must provide low-latency reads globally and consistent writes per user. Explain replication topologies (active-active vs active-passive), techniques for conflict resolution (last-writer-wins, CRDTs, per-user leader), read-routing strategies, leader-election for writes, and how to handle cross-region failover including DNS, health checks, and replication lag mitigation.
EasyTechnical
78 practiced
Describe backend testing strategies: unit tests, integration tests, contract tests, end-to-end tests, and smoke tests. For a payment-processing service, map out which kinds of tests you'd write, what each test validates, and how frequently each test suite should run in CI/CD. Include ideas for testing external dependencies like payment gateways.
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