I started with the obvious stuff, DNS failure, CDN issues, and then tried to work my way into the less obvious layers like quota exhaustion or a bad config push.
Structure your answer by categorizing failure modes across the stack—from infrastructure and dependencies to software and operational errors—and explain how they could cascade into a full outage. Emphasize that large-scale systems are designed for resilience, so a total outage typically requires multiple simultaneous failures or a systemic issue like a bad configuration push.
Pro tip: Mention that even with redundancy, correlated failures (e.g., a bad config affecting all regions) or dependency failures (e.g., DNS, BGP) can bring down the entire platform, and highlight the importance of blast radius reduction and graceful degradation.
Break down the system into layers: infrastructure (power, network, hardware), platform services (DNS, load balancers, databases), application code, and external dependencies. This ensures comprehensive coverage.
For each domain, list specific triggers such as natural disasters, cyberattacks, software bugs, misconfigurations, or third-party outages. Explain how they could lead to a full outage.
Describe how a failure in one component can propagate: e.g., a database outage causing retries that overload other services, or a bad config rollout affecting all regions simultaneously.
Highlight how systems like YouTube are designed to prevent total outages: redundancy, isolation, circuit breakers, canary deployments, and graceful degradation. Note that a total outage implies these safeguards failed.
Summarize that while total outages are rare, they can happen due to unforeseen correlated failures, and discuss the trade-offs between complexity, cost, and reliability.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.