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Lambda·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Jun 2026Remote

Summary

Lambda system design round for a software engineer role. The whole interview was basically one giant question about building an AI inference platform, and it went in a lot of directions fast.

Questions Asked (5)

Q1

Design a cloud-based AI inference platform that handles both real-time and batch workloads. Walk through model packaging and versioning, hardware selection, autoscaling, request routing, and multi-tenant isolation.

System DesignTechnical Trade-offs
Author's notes

This is a beast of a question and I spent probably too long on the hardware selection piece.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then propose a high-level architecture that separates real-time and batch paths but shares common infrastructure. Walk through each component (model packaging, hardware, autoscaling, routing, isolation) in a logical order, highlighting trade-offs and Lambda-specific optimizations like GPU utilization and cost efficiency.

Pro tip: Emphasize the importance of observability and cost monitoring from day one, and discuss how you would handle model rollbacks and A/B testing to ensure reliability and continuous improvement.

1. Clarify Requirements and Scale

Ask about expected request volume, latency SLAs, model sizes, and tenant count to inform design decisions. Establish whether the platform must support both real-time (low latency) and batch (high throughput) workloads.

2. Design Model Packaging and Versioning

Propose a standardized model format (e.g., ONNX, TorchScript) and a versioning scheme with immutable artifacts stored in a registry. Include metadata for dependencies and hardware requirements.

3. Select Hardware and Autoscaling Strategy

Choose GPU types based on model needs (e.g., NVIDIA A100 for large models, T4 for cost-effective inference). Implement autoscaling using metrics like GPU utilization, queue depth, and request latency, with separate policies for real-time and batch.

4. Implement Request Routing and Multi-Tenant Isolation

Use a load balancer and API gateway to route requests to appropriate model servers. For multi-tenancy, isolate tenants via namespaces, resource quotas, and network policies; consider dedicated instances for high-security tenants.

5. Address Trade-offs and Operational Concerns

Discuss trade-offs between latency and cost, cold start mitigation, and monitoring. Highlight how the design supports canary deployments and rollbacks.

Key Points to Mention

  • Model packaging: containerization (Docker) with dependencies, or specialized formats like ONNX for portability.
  • Versioning: semantic versioning, immutable artifacts, and a model registry (e.g., MLflow, custom S3-based).
  • Hardware selection: GPU vs. CPU, inference-optimized instances (e.g., AWS Inferentia), and spot instances for batch.
  • Autoscaling: Kubernetes HPA with custom metrics, KEDA for event-driven scaling, and predictive scaling for batch jobs.
  • Request routing: intelligent routing based on model version, tenant, and load; use of service mesh for traffic management.
  • Multi-tenant isolation: resource quotas, network policies, and separate namespaces; consider security and compliance requirements.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

How would you handle latency and throughput targets for the platform, and what cost control mechanisms would you put in place, like right-sizing or spot instance usage?

System DesignTechnical Trade-offs
Author's notes

Felt more comfortable here.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the workload characteristics and SLOs, then propose a layered strategy that balances performance and cost. Emphasize data-driven decisions: measure, set targets, implement controls, and continuously optimize. Highlight trade-offs and how you would validate them with experiments.

Pro tip: Tie cost controls directly to performance metrics—e.g., use spot instances for fault-tolerant batch jobs but keep latency-sensitive services on on-demand or reserved capacity. Show you understand that right-sizing is iterative and requires monitoring and automation.

1. Clarify requirements and constraints

Ask about workload types (e.g., batch vs. real-time), expected traffic patterns, latency SLOs, throughput targets, and budget constraints. This ensures your answer is tailored to the actual needs.

2. Define performance targets and metrics

Propose specific, measurable targets (e.g., p99 latency < 100ms, throughput > 10k RPS) and the metrics you'll track (latency percentiles, error rates, resource utilization). Explain how you'll monitor them.

3. Design for latency and throughput

Outline architectural choices: caching, sharding, async processing, autoscaling, and load balancing. Discuss trade-offs between consistency, availability, and latency.

4. Implement cost controls

Describe mechanisms like right-sizing instances based on utilization data, using spot instances for interruptible workloads, reserved instances for steady-state, and autoscaling to match demand. Mention tagging and cost allocation for visibility.

5. Monitor, iterate, and optimize

Explain how you'll continuously monitor performance and cost, set alerts, and run experiments (e.g., A/B tests, load tests) to find optimal configurations. Emphasize automation and feedback loops.

Key Points to Mention

  • Latency SLOs and percentile-based monitoring (p50, p95, p99)
  • Throughput capacity planning and autoscaling policies
  • Right-sizing based on historical utilization and performance profiling
  • Spot instances for fault-tolerant, stateless, or batch workloads
  • Reserved instances or savings plans for predictable baseline load
  • Cost allocation tags and budget alerts to track spending
  • Trade-offs between cost, performance, and reliability (e.g., spot interruptions)

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q3

What observability would you build into this platform, specifically around tracing and metrics for inference requests?

System DesignProduct Analytics & Metrics
Author's notes

Talked through distributed tracing across the request path, per-model latency histograms, GPU utilization metrics, and queue depth for batch jobs.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the platform's architecture and inference workload characteristics, then propose a layered observability strategy that covers the full request lifecycle. Focus on tracing to pinpoint latency bottlenecks and metrics to monitor system health, cost, and model performance. Emphasize actionable insights and integration with existing tools.

Pro tip: Tie observability directly to business outcomes like cost per inference and SLA compliance, and mention how you'd use sampling and cardinality control to keep telemetry affordable at scale.

1. Clarify scope and requirements

Ask about the platform's architecture (e.g., serverless, GPU clusters), traffic patterns, and existing observability stack to tailor your answer.

2. Design distributed tracing

Propose end-to-end tracing with unique request IDs, instrumenting key components like API gateways, model servers, and data pipelines to capture latency and errors.

3. Define key metrics

Outline metrics across four categories: system (CPU/GPU, memory), application (request rate, latency percentiles, error rates), model (accuracy, drift), and business (cost per inference, throughput).

4. Implement collection and storage

Suggest tools like OpenTelemetry for instrumentation, Prometheus for metrics, and Jaeger for traces, with sampling and aggregation to manage data volume.

5. Enable analysis and alerting

Describe dashboards for real-time monitoring, anomaly detection, and alerts tied to SLOs, ensuring observability drives action.

Key Points to Mention

  • Distributed tracing with context propagation across microservices and inference pipelines
  • Latency breakdown: queue time, preprocessing, model inference, postprocessing
  • Key metrics: p50/p95/p99 latency, error rates, throughput, GPU utilization, cost per request
  • Model-specific metrics: prediction drift, data drift, accuracy over time
  • Use of OpenTelemetry, Prometheus, Grafana, and Jaeger as standard tools
  • Sampling strategies and cardinality control to balance detail and cost

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q4

How would you safely roll out new model versions, and what strategies would you use to catch regressions before full deployment?

A/B Testing & ExperimentationSystem Design
Author's notes

Canary and shadow mode, covered both.

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AI HintsAI Generated

Suggested Approach

Start by outlining a phased rollout strategy that includes offline evaluation, shadow deployment, canary releases, and A/B testing. Then describe specific regression detection techniques such as automated metrics monitoring, statistical tests, and rollback triggers. Emphasize safety, observability, and iterative improvement.

Pro tip: Define clear rollback criteria and automate the rollback process to minimize downtime and impact. Also, consider using feature flags to decouple deployment from release, allowing quick toggling without redeploying.

1. Offline Evaluation

Evaluate the new model on a held-out test set and compare against the current production model using relevant metrics. Ensure the new model meets performance thresholds before proceeding.

2. Shadow Deployment

Deploy the new model in parallel with the existing one, sending it a copy of live traffic without affecting user experience. Compare predictions and monitor for discrepancies or performance issues.

3. Canary Release

Roll out the new model to a small percentage of users (e.g., 1-5%) while monitoring key metrics closely. Gradually increase traffic if no regressions are detected.

4. A/B Testing

Run a controlled experiment where a portion of users get the new model and others get the old one. Use statistical tests to determine if the new model significantly improves or degrades key metrics.

5. Full Deployment and Monitoring

Once the new model passes all checks, roll it out to all users. Continuously monitor performance and set up alerts for anomalies, with a rollback plan ready.

Key Points to Mention

  • Offline evaluation metrics (e.g., accuracy, precision, recall, latency)
  • Shadow deployment to compare predictions without user impact
  • Canary releases with gradual traffic increase and automated rollback
  • A/B testing with statistical significance and guardrail metrics
  • Monitoring and alerting for model performance and data drift
  • Feature flags for decoupling deployment and release

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q5

How would you integrate this platform with Kubernetes and a model registry, and how does your design compare to existing industry solutions?

System DesignAPI & Integrations
Author's notes

The Kubernetes integration part was fine, talked about custom operators, CRDs for model deployments, and hooking into the model registry for artifact resolution at deploy time.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the platform's core capabilities and the integration goals, then outline a Kubernetes-native architecture that connects to a model registry for model lifecycle management. Compare your design to existing solutions like Kubeflow, MLflow, and SageMaker, highlighting trade-offs in scalability, ease of use, and vendor neutrality.

Pro tip: Emphasize operational simplicity and cost-efficiency, as Lambda focuses on GPU cloud and serverless AI—show how your design minimizes infrastructure overhead while maximizing performance.

1. Clarify Requirements and Assumptions

Ask clarifying questions about the platform's purpose, scale, and existing components. State assumptions about Kubernetes version, model registry choice (e.g., MLflow, Kubeflow), and integration constraints.

2. Design Kubernetes Integration

Propose using Kubernetes operators or custom controllers to manage platform resources. Describe how to deploy platform components as pods, services, and CRDs, and how to handle scaling, networking, and storage.

3. Integrate with Model Registry

Explain how the platform will interact with the model registry for model versioning, metadata, and artifact storage. Cover authentication, API calls, and synchronization mechanisms (e.g., webhooks, polling).

4. Compare with Industry Solutions

Contrast your design with existing solutions like Kubeflow, MLflow, SageMaker, and Vertex AI. Discuss trade-offs in terms of flexibility, managed services, cost, and lock-in.

5. Summarize Benefits and Trade-offs

Conclude with the key advantages of your approach (e.g., scalability, portability) and acknowledge potential challenges (e.g., complexity, maintenance).

Key Points to Mention

  • Kubernetes operators and custom resource definitions (CRDs) for platform management
  • Model registry APIs and artifact storage (e.g., S3, GCS) for model versioning
  • Service mesh or ingress for secure communication between platform and registry
  • Comparison with Kubeflow Pipelines, MLflow, and managed services like SageMaker
  • Scalability and resource management using Kubernetes autoscaling and GPU scheduling
  • Security considerations: RBAC, secrets management, and network policies

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.