Rafael demonstrated strong command over system design fundamentals and drove the CI/CD orchestration session with clarity and ownership. The conversation flowed well from requirements to high-level architecture and touched on multiple critical deep-dive areas.

Areas of Strength Included:

• Quickly framed functional requirements, and partially covered non-functional requirements such as fairness and sandboxing.
  
  
• Built a step-by-step high-level design, with room for deep dives and iterative refinements — a good structure for this type of system.
  
  
• Demonstrated a solid understanding of core entities, such as artifacts, tasks, and DAGs, and how they relate (e.g., avoiding redundant builds if an artifact already exists).
  
  
• Proactively explored communication protocols (SSE vs. consumer groups) and storage trade-offs (memory vs. relational DB vs. S3).
  
  
• Designed effective deduplication mechanisms, discussing cache keys (e.g., repo+provider+sha), TTL management, and Redis usage.
  
  
• Proposed scalable job orchestration, with concepts like virtual queues and per-type schedulers to handle varying workloads.
  
  
• Addressed hot partitioning issues, offering quota-based fairness controls at the algorithm level.
  
  
• Strong handling of failure scenarios: covered retries with backoff, cancellation patterns (e.g., SIGKILL), and zombie job cleanup via heartbeat mechanisms.
  
  

Areas for Improvement:

• Estimation Accuracy: Scale estimations need to be more precise and clearly distinguish average vs. spike traffic. Emphasize burst handling, as that's where real-world bottlenecks often arise.
  
  
• Execution Flow Modeling: Strengthen the end-to-end narrative from initiation → scheduling → execution → post-processing. This helps highlight where system responsibilities shift across components.
  
  
• State Machine & Retry Flow: Be prepared to go deeper into execution state modeling:
  
  
  
  • Clarify how Task and TaskAttempt entities evolve — does the task change state, or only its attempts?
    
    
  • In retry logic, include start time, retry index, and backoff policy in your model.
    
    
  • Discuss what is logged at each retry or failure event.
    
    
  • When autoscaling, define which node owns the retry and how task transitions are coordinated.
    
    
  • For chaining tasks (e.g., Task 3 triggered by Task 2), cover best practices in dependency tracking and readiness checks.
    
    
• Reconciliation Mechanism: Timeout and cancellation handling should explicitly mention a reconciler service, responsible for surfacing and cleaning up stale jobs in large-scale systems.
  

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