What's the most cost-effective way to monitor thousands of source sites using a webhook-based feed monitor?

The most cost-effective approach is usually:

1) Don’t monitor every page directly — monitor the feed source layer

If the sites expose RSS/Atom feeds, sitemap.xml, changelogs, /news endpoints, or APIs, use those instead of scraping HTML pages.
That cuts bandwidth, parsing cost, and false positives dramatically.

2) Use a webhook-first architecture

Instead of polling each site constantly:

• Your monitor checks sources on a schedule
• When it detects a change, it pushes a webhook event to your system
• Downstream systems react only when needed

This is cheaper than having many consumers polling independently.

3) Batch and tier your polling frequency

For thousands of sources, don’t use one interval for all:

• High-priority sites: frequent checks
• Medium-priority: moderate checks
• Low-priority: sparse checks

A common cost-saving tactic is to:

• Check ETag / Last-Modified first
• Only fetch full content when those change

4) Use a change-detection pipeline

A good low-cost pipeline looks like:

1. Fetch lightweight headers or feed metadata
2. Compare hash / timestamp / etag
3. If changed, fetch the full item/page
4. Normalize and dedupe
5. Emit webhook only for meaningful changes

This avoids processing noise like ad changes, timestamps, or layout shifts.

5) Run serverless or autoscaled workers

For cost efficiency at scale:

• Serverless for bursty workloads
• Autoscaled containers/VMs for steady high-volume monitoring

Avoid always-on oversized infrastructure if load is uneven.

6) Store state cheaply

Keep per-source state minimal:

• last seen etag
• last modified time
• content hash
• last successful check
• retry count

A small key-value store is often enough and much cheaper than heavy databases.

7) Deduplicate and debounce webhook events

If many sources update at once, aggregate:

• combine repeated updates
• suppress duplicate events
• send one webhook per meaningful change window

This saves compute and reduces downstream load.

Most cost-effective practical setup

If you want the cheapest reliable model for thousands of sources:

• Prefer RSS/Atom/sitemaps/APIs
• Poll lightly using ETag/Last-Modified
• Use serverless workers
• Keep state in a cheap KV store
• Trigger webhooks only on actual changes
• Batch and dedupe aggressively

If you want the absolute cheapest option

If acceptable for your use case:

• Use a managed feed-monitoring service or scraping platform with webhook output
• Or rely on third-party change-detection APIs rather than building/hosting your own

This can be cheaper operationally than running custom infrastructure, especially if you value engineering time more than infrastructure cost.

If you want, I can sketch a low-cost architecture for 1k / 10k / 100k sources with rough cost drivers.