Had seen this one before so I wasn't going in blind.
Start by clarifying requirements and scale, then outline a high-level architecture with key components like URL frontier, fetcher, parser, and storage. Dive into critical design decisions such as partitioning, deduplication, politeness, and fault tolerance, and discuss trade-offs between consistency, availability, and performance.
Pro tip: Emphasize the importance of a distributed URL frontier with consistent hashing and a two-level deduplication strategy (in-memory Bloom filters + persistent storage) to balance efficiency and accuracy. Also, proactively discuss how to handle dynamic content and JavaScript rendering, as Meta's crawler likely deals with complex web apps.
Ask questions to understand the scope: expected number of pages, crawl rate, freshness requirements, politeness constraints, and whether dynamic content needs rendering. Establish assumptions for the design.
Sketch the main components: URL frontier (scheduler), fetcher nodes, parser, content storage, and deduplication service. Explain how they interact and scale horizontally.
Detail the design of the URL frontier (partitioning, prioritization, politeness), deduplication (Bloom filters, checksums), and fault tolerance (retries, checkpointing). Discuss trade-offs.
Explain how to handle node failures, dynamic scaling, and monitoring. Discuss consistency models for deduplication and storage, and how to avoid overloading target servers.
Summarize key decisions, mention potential bottlenecks, and suggest future improvements (e.g., using ML for prioritization). Be prepared to discuss alternatives.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.