Web Crawling at Scale: Architecture and Optimization Strategies

Building a web crawler that can process millions of pages requires careful architectural decisions. This article covers the multi-worker architecture pattern where a coordinator distributes URLs from a priority queue while workers fetch and process pages concurrently. Key optimization strategies include DNS caching, connection pooling, adaptive politeness delays, and incremental crawling using ETag and Last-Modified headers. We examine content extraction using techniques like DOM-based article extraction, boilerplate removal, and structured data parsing from JSON-LD and microdata. Error handling patterns cover retry strategies, circuit breakers for unresponsive hosts, and graceful degradation when facing rate limits or CAPTCHAs. The article includes real benchmarks showing how these optimizations reduced crawl time from 48 hours to 6 hours for a 500,000-page site.