Production Hardening

The defaults in this repo’s wrangler.json are tuned for the bundled demo - ALLOWED_ORIGINS = "*", no caller allowlist, no quality cap. Useful for “paste any URL” exploration; wrong for anything you’ll link to publicly.

This page is a one-stop checklist. If you skip the docs and only do these five things, your Worker stays cheap and your bill stays predictable.

1. Lock down ALLOWED_ORIGINS

ALLOWED_ORIGINS controls which upstream URLs the Worker can fetch from. The demo uses "*" so the playground works for any pasted URL, that makes the Worker an open proxy. Replace with a curated comma-separated list:

"ALLOWED_ORIGINS": "https://cdn.yoursite.com,https://images.unsplash.com"

Path-relative requests (?url=/photo.jpg) are always fetched from ORIGIN and don’t depend on this list, but every absolute https:// URL must match.

2. Set ALLOWED_REFERERS (caller allowlist)

ALLOWED_ORIGINS controls what we fetch. ALLOWED_REFERERS controls who can call us. Without it, anyone on the internet can hit your Worker URL and you pay the CPU.

"ALLOWED_REFERERS": "https://yoursite.com,https://www.yoursite.com"

Behavior:

• Unset: any caller allowed (demo behavior).
• Set: requests with a non-matching Referer (or Origin) header get 403 Forbidden referer.
• Same-origin is always allowed, the Worker can serve its own bundled demo / static assets without you adding the Worker URL to the list.
• Missing Referer is rejected when this is set. Browsers typically send a Referer for <img> requests; if your traffic comes through a strict Referrer-Policy: no-referrer header, leave ALLOWED_REFERERS unset and rely on rate-limiting + spend caps instead.

3. Cap quality with MAX_QUALITY

A caller can request ?q=100 and force expensive encodes. Cap it:

"MAX_QUALITY": "85"

Quality 85 is visually indistinguishable from 100 for typical web photos and encodes meaningfully faster (especially for AVIF). Values above the cap are silently clamped, the loader’s emitted srcSet keeps working without errors.

4. Decide which formats you serve

DISABLED_FORMATS lets you trade quality for cost without redeploying. It’s a comma-separated list (recognized: jpeg, png, webp, avif, gif, svg). The biggest CPU win is dropping AVIF:

"DISABLED_FORMATS": "avif"

The negotiator then picks WebP for AVIF-capable browsers, about 60–80% of AVIF’s compression gains at a fraction of the encode cost. Re-enable later by removing it from the list in the Cloudflare dashboard. You can also drop passthrough surfaces, DISABLED_FORMATS="svg,gif" rejects SVG and animated GIF inputs with 415.

5. Set platform-level guardrails (Cloudflare dashboard)

These are not edgesharp settings, they’re Cloudflare features you should turn on for any public Worker:

• Workers spend cap alert: emails you when monthly Worker spend crosses a threshold. Set this before you make the URL public. The first time you’ll need it is exactly the time you can’t predict.

• Rate Limiting on /_next/image: e.g., 100 requests/min per IP. The CPU cost of a single cold transform is small; the cost of a thousand of them in a minute isn’t.

• Bot Fight Mode: catches the obvious abuse patterns without per-rule configuration.

• R2 lifecycle rule: bound your L2 cache size. 30-day expiration is reasonable for a CDN cache:

  npx wrangler r2 bucket lifecycle set edgesharp-cache \
    --rule '{"id":"expire-30d","enabled":true,"conditions":{"prefix":"v1/"},"expiration":{"days":30}}'

Recommended production wrangler.json

{
  "name": "edgesharp",
  "main": "src/worker.ts",
  "compatibility_date": "2026-03-28",
  "vars": {
    "ORIGIN": "https://yoursite.com",
    "ALLOWED_ORIGINS": "https://cdn.yoursite.com",
    "ALLOWED_REFERERS": "https://yoursite.com,https://www.yoursite.com",
    "MAX_QUALITY": "85"
  }
  // ...assets, durable_objects, r2_buckets, rules, migrations
}

That config + the platform-level items above is what stands between “demo I shared with my team” and “Worker I forgot about that ran up a bill when an AI crawler discovered it.”

What this doesn’t protect against

• Authenticated abuse: if a caller can make the right Referer header (server-side requests, Postman), the allowlist doesn’t stop them. Pair with rate-limiting on the platform layer.
• Compromised allowed origins: if cdn.yoursite.com is XSS’d or hijacked, the Worker will fetch whatever’s there. Image content-type validation is enforced (no SVG, no executables) but compromised images can still cost CPU.
• Surge billing on Paid: beyond the 10M included requests/month, $0.30 per million keeps charging. The spend cap alert above is what tells you a bad day is happening.