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This question is commonly asked for Software Engineer candidates at Anthropic during technical interviews.

Design a scalable web crawler | Anthropic Interview Question

Quick Overview

This question evaluates understanding of scalable web crawler architecture, distributed systems concepts, URL and content deduplication, scheduling and prioritization, storage and metadata design, and operational concerns such as politeness, rate limiting, DNS/connection management, and fault tolerance.

System Design: Scalable Web Crawler

Context

Design a production-ready web crawler that discovers and downloads publicly accessible web pages at internet scale. Your design should support continual discovery, politeness (respect for publishers), and high throughput while avoiding duplicates and crawler traps.

Assume we start with a list of seed URLs and aim to crawl and recrawl billions of pages over time. The crawler should be modular so it can run on a single machine for small jobs and scale out to a distributed cluster.

Requirements

Architecture
- Define core components: URL frontier, fetchers, parsers, storage, metadata/indexing, and coordination.
- Include DNS resolution, connection management, and content-type handling.
Robots and Politeness
- How to fetch and cache robots.txt; obey user-agent rules and crawl-delay directives.
- Per-host/per-domain rate limiting and connection concurrency.
Deduplication
- URL deduplication via canonicalization and a global "seen" structure.
- Content deduplication (exact and near-duplicate pages).
Prioritization and Scheduling
- How to prioritize which URLs to crawl next (e.g., depth, quality, freshness, domain budgets).
- Recrawl scheduling for freshness.
Storage and Metadata
- Where to store raw content (blobs) and structured metadata (fetch status, fingerprints, link graph, robots cache).
Scale and Throughput Targets
- Make reasonable assumptions (e.g., initial 100M URLs, ~10k fetches/sec target) and reflect them in your choices.
Follow-up: Concurrency and Distribution
- Extend to multithreaded and multi-machine operation.
- Explain: concurrency controls, per-host rate limiting, back-pressure, fault tolerance, and processing semantics (exactly-once vs at-least-once).

Deliverables: A clear architecture, key data structures and algorithms, scheduling logic, and operational considerations.

Quick Overview

Context

Requirements

Architecture

Define core components: URL frontier, fetchers, parsers, storage, metadata/indexing, and coordination.
Include DNS resolution, connection management, and content-type handling.

Robots and Politeness

How to fetch and cache robots.txt; obey user-agent rules and crawl-delay directives.
Per-host/per-domain rate limiting and connection concurrency.

Deduplication

URL deduplication via canonicalization and a global "seen" structure.
Content deduplication (exact and near-duplicate pages).

Prioritization and Scheduling

How to prioritize which URLs to crawl next (e.g., depth, quality, freshness, domain budgets).
Recrawl scheduling for freshness.

Storage and Metadata

Where to store raw content (blobs) and structured metadata (fetch status, fingerprints, link graph, robots cache).

Scale and Throughput Targets

Make reasonable assumptions (e.g., initial 100M URLs, ~10k fetches/sec target) and reflect them in your choices.

Follow-up: Concurrency and Distribution

Extend to multithreaded and multi-machine operation.
Explain: concurrency controls, per-host rate limiting, back-pressure, fault tolerance, and processing semantics (exactly-once vs at-least-once).

Deliverables: A clear architecture, key data structures and algorithms, scheduling logic, and operational considerations.

Design a scalable web crawler

Quick Overview

System Design: Scalable Web Crawler

Context

Requirements

Solution

Comments (0)

Design a scalable web crawler

Quick Overview

System Design: Scalable Web Crawler

Context

Requirements

Solution

Comments (0)