Web Crawler / Search Indexer
Discover pages, crawl them, extract content, and index for search.
AdvancedDataPlatform
A crawler scheduler discovers seeds and URLs, a fetcher retrieves pages, an extractor parses content, and an indexer writes the resulting document corpus into a search index for downstream retrieval.
When to use it
- You need to create a search engine or content discovery system over a large public or private web surface
- Discovery and indexing are naturally batch-like and can tolerate a best-effort crawl
Trade-offs
- Crawling the open web means dealing with robots.txt, rate limits, duplicate content and legal constraints
- A crawler can be operationally expensive if it needs to be polite and resilient at scale
Components used
Batch / Scheduled JobContainer ServiceStream ProcessingSearch IndexMessage QueueRelational Database
How it works
- A frontier queue holds URLs to visit. Fetchers pull from it, download pages, extract links, and feed newly discovered URLs back in.
- A seen-set prevents revisiting the same URL, and politeness rules rate-limit requests per host regardless of how many are queued.
- Extracted content is parsed and written to a search index separately from the crawling loop.
Used in the wild
- Search engine indexing.
- Price and content monitoring across competitor sites.
- Building training or retrieval corpora from public web content.
Good to know
- Crawler traps are everywhere: infinite calendars, session ids in URLs and faceted navigation generate unbounded unique URLs that will consume the frontier forever without depth and pattern limits.
- Politeness is what keeps you unblocked. Respecting robots.txt and per-host delays matters more to a crawler's long-term throughput than raw fetch concurrency.
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