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

SeniorPrefer not to say
Jun 2026Remote

Summary

A system design round at OpenAI that went sideways fast. The interviewer kept pivoting topics mid-discussion, and the whole thing felt like we were both lost in different conversations. CI/CD, image caching, S3 uploads... none of it ever clicked into a coherent thread.

Questions Asked (4)

Q1

Given a CI/CD system that reads workflow definitions from YAML and runs jobs sequentially, how would you add build caching to it?

System DesignTechnical Trade-offsAdaptability & Ambiguity
Author's notes

I got completely turned around here.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a design that integrates caching into the YAML schema and job execution flow. Focus on cache key generation, storage, invalidation, and trade-offs between simplicity and performance.

Pro tip: Emphasize incremental delivery: start with a simple cache keyed on job inputs and expand later. This shows pragmatism and awareness of real-world constraints.

1. Clarify Requirements and Constraints

Ask about cache scope (per job, per workflow, global), storage options, security, and expected performance gains. This ensures the design meets actual needs.

2. Extend YAML Schema for Cache Configuration

Define new YAML fields (e.g., cache: {key: ..., paths: ...}) to let users specify what to cache and how to key it. Ensure backward compatibility.

3. Design Cache Key and Storage Strategy

Propose a cache key derived from job inputs, environment, and dependencies (e.g., hash of lockfiles). Choose a storage backend (local, S3, Redis) based on trade-offs.

4. Integrate Caching into Job Execution

Modify the runner to check for cache before job execution, restore if hit, and save after success. Handle cache misses and failures gracefully.

5. Address Invalidation, Eviction, and Monitoring

Define TTL, size limits, and invalidation triggers. Add metrics for hit rate and storage usage to monitor effectiveness.

Key Points to Mention

  • Cache key generation: deterministic hashing of inputs, dependencies, and environment
  • Storage options: local disk, network filesystem, object storage (S3), or dedicated cache service
  • YAML schema design: backward compatibility, defaults, and user control
  • Cache invalidation strategies: TTL, versioning, and explicit invalidation
  • Trade-offs: simplicity vs. performance, cost, and complexity
  • Security: cache poisoning prevention, access control, and isolation

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

Q2

How would you support custom image layers in that same CI/CD pipeline?

System DesignTechnical Trade-offs
Author's notes

She asked this right alongside the caching question but we never actually got to it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the current CI/CD pipeline setup and the specific need for custom image layers. Then, propose a solution that integrates image building into the pipeline, leveraging tools like Docker and caching strategies, while addressing trade-offs around build time, security, and reproducibility.

Pro tip: Emphasize the importance of layer caching and immutable tags to optimize build times and ensure consistency across environments. Also, mention how you would handle security scanning of custom layers to prevent vulnerabilities.

1. Clarify Requirements

Ask questions to understand the current pipeline, the purpose of custom image layers, and any constraints (e.g., build time, security policies).

2. Design Integration

Outline how to incorporate image building into the pipeline, such as adding a build stage that uses Dockerfiles or Buildpacks, and how to trigger builds on code changes.

3. Optimize Build Process

Discuss strategies to optimize image builds, including layer caching, multi-stage builds, and parallelization, to reduce build times and resource usage.

4. Ensure Security and Compliance

Explain how to integrate security scanning (e.g., Trivy, Clair) and signing (e.g., Cosign) into the pipeline to maintain security and compliance.

5. Address Trade-offs

Acknowledge trade-offs such as increased complexity, build time, and maintenance overhead, and propose mitigation strategies.

Key Points to Mention

  • Use of Docker or OCI-compliant image building tools
  • Layer caching and multi-stage builds for efficiency
  • Integration with existing CI/CD tools (e.g., Jenkins, GitLab CI, GitHub Actions)
  • Security scanning and vulnerability management
  • Immutable tags and versioning for reproducibility
  • Trade-offs between build speed, image size, and security

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

Q3

If two jobs in the pipeline use different compilers with different dependencies, how do you handle the cache between them?

System DesignAdaptability & Ambiguity
Author's notes

Didn't understand this one at all when she first asked it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the caching mechanism (e.g., content-addressable, key-based) and the build system. Explain that cache keys must incorporate compiler identity and dependency versions to avoid collisions, then discuss strategies like namespacing, separate caches, or cache invalidation.

Pro tip: Emphasize that correctness and reproducibility trump cache hit rate; it's better to miss a cache than to serve a stale artifact. Mention that you'd monitor cache effectiveness and adjust granularity as needed.

1. Clarify the caching system and build context

Ask or state assumptions about how the cache works (e.g., key-value store, content-addressable) and what build tool is used. This ensures your answer is relevant to the actual setup.

2. Identify cache key components

Explain that the cache key must include the compiler name/version, compiler flags, and all dependency versions (including transitive ones). This prevents cross-contamination between jobs.

3. Design isolation strategy

Propose using separate cache namespaces or prefixes for each compiler/dependency combination, or a single cache with fully qualified keys. Discuss trade-offs between isolation and storage efficiency.

4. Handle cache invalidation and updates

Describe how to invalidate or expire cache entries when compilers or dependencies change, such as version-based eviction or TTL policies.

5. Monitor and optimize

Mention tracking cache hit/miss rates and adjusting key granularity or isolation to balance performance and correctness.

Key Points to Mention

  • Cache key must include compiler identity (name, version, flags) and dependency versions.
  • Use namespacing or separate caches to isolate different toolchains.
  • Consider content-addressable caching where the hash includes all inputs.
  • Ensure cache invalidation when compilers or dependencies are updated.
  • Trade-off between cache hit rate and correctness/reproducibility.
  • Monitor cache effectiveness and adjust strategy as needed.

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

Q4

How would you handle partial or failed chunk uploads when uploading build artifacts to S3?

System DesignTechnical Trade-offs
Author's notes

This one came out of nowhere and I couldn't see how it connected to anything we'd discussed.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the constraints: artifact size, network reliability, and S3 multipart upload limits. Then describe a robust strategy using S3 multipart uploads with retries, checksums, and cleanup of incomplete uploads, emphasizing trade-offs between simplicity and resilience.

Pro tip: Mention that S3 multipart uploads allow resuming from the last successful part, but you must handle part-level retries and abort incomplete uploads to avoid storage costs. Also, use checksums to detect corruption early.

1. Clarify requirements and constraints

Ask about artifact size, network conditions, and whether uploads need to be resumable. This shows you tailor solutions to context.

2. Leverage S3 multipart upload

Explain that S3 multipart upload splits large objects into parts, each uploaded independently with its own ETag. This enables parallel uploads and resuming from failed parts.

3. Implement retry and backoff

For each part, use exponential backoff with jitter on retries. Track which parts succeeded and only re-upload failed ones.

4. Ensure integrity and cleanup

Use checksums (e.g., MD5 or SHA-256) to verify each part and the final object. Abort incomplete multipart uploads after a timeout to avoid orphaned parts and costs.

5. Discuss trade-offs and alternatives

Compare with single PUT uploads, using S3 Transfer Acceleration, or client-side chunking with a manifest. Highlight trade-offs in complexity, cost, and performance.

Key Points to Mention

  • S3 multipart upload API: initiate, upload part, complete, abort
  • Part-level retries with exponential backoff and jitter
  • Checksums for data integrity (e.g., Content-MD5, SHA-256)
  • Lifecycle policies to abort incomplete multipart uploads
  • Concurrency control and part size selection (e.g., 5 MB to 5 GB)
  • Trade-offs: simplicity vs. resilience, cost of orphaned parts, network overhead

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