Do I need retries and backoff in a crawler?

Yes — in most crawlers, retries with backoff are strongly recommended.

Why

Crawling the web is noisy and failure-prone:

• Transient network issues: timeouts, DNS hiccups, connection resets
• Server-side throttling: 429, 503, temporary bans
• Intermittent upstream failures: pages that fail once and succeed on retry

Without retries, you’ll lose data and waste crawl budget. Without backoff, you can accidentally make problems worse by hammering a struggling site.

What to retry

Typically retry on:

• 5xx responses: 500, 502, 503, 504
• 429 Too Many Requests
• Network exceptions: timeouts, connection errors, temporary TLS issues

Usually avoid retrying on:

• 4xx client errors like 404, 403, 400
• Permanent parsing failures
• Invalid URLs

How to back off

Use exponential backoff with jitter:

• First retry after a short delay
• Increase delay each attempt
• Add random jitter so many crawler workers don’t retry in sync

Example pattern:

• Retry 1: 1s
• Retry 2: 2s
• Retry 3: 4s
• Retry 4: 8s
• Add randomness around each delay

Best practices

• Keep retries limited, e.g. 2–5 attempts
• Use per-host rate limiting
• Respect robots.txt and crawl-delay if applicable
• Set timeouts so hung requests don’t stall workers
• Log retry reasons and final failures

Caveat

For a crawler that hits a very large number of mostly static pages, you may want different retry policies by error type:

• Network/5xx: retry
• 429: retry with longer backoff
• 404: no retry
• 403: maybe retry once, but often treat as blocked

If you want, I can also suggest a simple retry/backoff policy for a crawler in Python, Go, or Node.