I started with the BFS queue and dedup set, which went fine.
Start by clarifying requirements (scale, politeness, depth limits) and then outline a BFS crawler using a queue, a visited set for deduplication, and URL normalization. Discuss domain restriction, concurrency, and trade-offs like politeness vs. throughput, and finish with edge cases and testing.
Pro tip: Mention robots.txt and crawl-delay early to show respect for web etiquette and avoid legal issues, and propose a distributed architecture with a URL frontier and worker pool to demonstrate scalability thinking.
Ask about scale (pages, depth), politeness (robots.txt, rate limiting), and whether to restrict to same domain. Confirm expected output and error handling.
Use a queue for BFS, a set for visited URLs, and a function to normalize URLs (lowercase host, remove fragments, sort query params). Explain how to extract links from HTML.
Check if a URL belongs to the same domain (or subdomain) before enqueueing. Normalize URLs before deduplication to avoid duplicates with different representations.
Discuss concurrency (thread pool, async I/O), rate limiting per domain, and distributed crawling with a URL frontier. Mention robots.txt parsing and crawl-delay.
Cover malformed URLs, redirects, non-HTML content, and cycles. Suggest unit tests for normalization and integration tests with a mock server.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
I knew the general shape of the answer: catch exceptions, distinguish retryable vs non-retryable status codes, exponential backoff with a cap.
Structure your answer by categorizing failures into client errors (4xx), server errors (5xx), and network-level issues (timeouts, malformed URLs), then describe a layered handling strategy for each. Emphasize idempotency, exponential backoff with jitter, and circuit breakers to prevent cascading failures, aligning with Amazon's operational excellence and customer obsession principles.
Pro tip: Tie your retry logic to Amazon's leadership principles by highlighting how you balance customer impact (avoiding duplicate actions) with system resilience (retrying transient failures), and mention using AWS services like SQS or Step Functions for managed retries when appropriate.
Distinguish between client errors (4xx), server errors (5xx), and network issues (timeouts, DNS failures, malformed URLs). Explain that 4xx errors are generally non-retryable, while 5xx and network errors are candidates for retries.
For malformed URLs, validate and sanitize inputs before crawling, and log them for analysis without retrying. For timeouts, set reasonable timeouts per request and treat them as transient, but avoid retrying indefinitely.
Use exponential backoff with jitter to avoid thundering herd problems. Limit retries (e.g., 3-5 attempts) and consider idempotency to prevent duplicate side effects. Optionally, use a dead-letter queue for persistent failures.
Implement circuit breakers to stop retrying when a service is consistently failing, preventing resource exhaustion. Monitor error rates and retry counts to detect systemic issues and alert accordingly.
Explain trade-offs between retry aggressiveness and latency/cost. Mention how AWS services like SQS, Lambda, or Step Functions can offload retry logic and provide built-in resilience.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.