Lambda Interview Questions

Use pricing calculators, monitor billing dashboards, set budgets and alerts, and right-size resources. Lambda workloads may spike with traffic—plan autoscaling limits and reserved capacity where it saves money.

Apply least privilege: grant only actions required for Lambda, use roles over long-lived keys, and audit policies regularly. Mention resource-level permissions and separation between dev/staging/prod accounts.

Consider latency, data residency, failover, and replication lag. Use health checks, DNS failover or global load balancing, and test disaster recovery drills for Lambda critical paths.

VPCs, subnets, security groups/firewalls, private endpoints, and TLS termination. Explain how traffic flows from users to Lambda and which hops are encrypted or logged.

Enable encryption (KMS-managed keys), enforce HTTPS/TLS, restrict public access, and enable audit logs. Lambda should not expose sensitive data in URLs or client-side storage without additional protection.

Use centralized logging, metrics, traces, and dashboards native to the platform. Correlate Lambda errors with deployments and set SLOs so teams detect regressions before users report them.

Use the official AWS docs for Lambda, language or framework references, and reputable community guides. Bookmark release notes and migration guides when upgrading versions, since Lambda behavior can change between releases.

Copying snippets without understanding why Lambda works leads to fragile code. Beginners often skip error handling, tests, or edge cases. Slow down, trace execution step by step, and validate assumptions with small experiments.

Name the primary service (e.g., Lambda, S3, EC2, IAM) and adjacent ones (CloudWatch, VPC, KMS). Explain how Lambda maps to managed primitives instead of DIY servers when appropriate.

Identify billable dimensions (requests, GB-month, data transfer, provisioned capacity). Use Cost Explorer/budgets and right-size before optimizing Lambda architecture.

Roles over long-lived keys, resource-level ARNs, condition keys, and separate accounts for prod. Audit who can change Lambda permissions.

CloudWatch metrics/logs, X-Ray or OpenTelemetry traces, and alarms with runbooks. Correlate Lambda errors with deploys.

VPC placement, security groups, private endpoints, and TLS. Describe the path from client to Lambda.

SSE-KMS/CMKs, HTTPS, bucket policies or resource policies, and blocked public access where required. Rotate keys and audit Lambda access.

Single-AZ designs, missing alarms, oversized blast radius, or hardcoded regions. Explain a safer default for Lambda.

Follow team conventions, split concerns into testable units, handle edge cases, and document assumptions. Review similar modules in the codebase, add observability, and ship incrementally with feature flags if Lambda is risky.

Watch for bottlenecks, shared state races, config drift, and unbounded resource usage. Load-test Lambda paths, set limits, and plan horizontal scaling or caching before traffic spikes.

One approach optimizes simplicity and time-to-market; the other optimizes performance, flexibility, or compliance. Choose based on team skill, traffic, and maintenance horizon—there is rarely a single best answer for Lambda.

Reproduce in staging, check logs/metrics/traces, narrow scope with binary search deploys, and write a postmortem. Fix Lambda root cause, add regression tests, and improve alerts so similar failures are caught earlier.

Check correctness, tests, naming, error handling, security, and performance. Ask whether Lambda belongs in this layer, if docs updated, and if rollback is safe.