Cloudflare cache warming: why one server can't preload 300+ colos

Search for "preload Cloudflare cache" and you'll find the same recipe over and over: run a crawler over your sitemap, done. It feels right — and it barely works. To understand why, you need one fact about Cloudflare's architecture, and once you have it, everything about warming strategy falls into place.

The one fact: caches are per-colo

Cloudflare operates 300+ data centers ("colos"). When a visitor requests your page, anycast routing sends them to the nearest colo — and that colo's cache answers. There is no global Cloudflare cache. A page cached at FRA (Frankfurt) is entirely cold at NRT (Tokyo), GRU (São Paulo) and SYD (Sydney).

You can see this yourself: request the same URL through a VPN from two continents and compare the cf-ray header (the colo code is after the dash) and cf-cache-status. Frankfurt says HIT; Tokyo says MISS — for a URL you "warmed" minutes ago.

Why the single-server crawler fails

A crawler on your server (or a WordPress preload plugin, or a GitHub Action) sends all its requests from one place. Anycast routes them all to the same colo. Result: you've warmed exactly one edge location out of 300+ — usually the one closest to your origin, which is precisely where warming matters least, because your origin round trip is shortest there anyway.

Server-side preloading is still worthwhile for what's on your server: page caches, object caches, OPcache. Just don't expect it to move your Cloudflare hit ratio for visitors on other continents.

What about the Cache Reserve / paid options?

Cloudflare offers pieces of this puzzle natively. Tiered Cache (free) routes cache misses through larger upper-tier colos, so a miss in a small location can be answered by a regional hub instead of your origin. Cache Reserve (paid, R2-backed) keeps a persistent copy of cacheable assets so evictions hurt less. Both are worth enabling — and neither eliminates the cold-start: the first request per region is still slow, entries still expire, and the Workers Cache (below) is not covered by Cache Reserve at all.

The Workers Cache wrinkle

If your site renders in a Cloudflare Worker — Astro, Next.js on Workers, or a CMS like EmDash — your HTML is typically cached in the Workers Cache, which sits in front of the Worker. It's also per-colo, and it has an extra property: zone-level purge ("Purge Everything") doesn't touch it, and Cache Rules don't apply to it. It's controlled by response headers (Cloudflare-CDN-Cache-Control, Cache-Tag) and the Workers Cache purge API. For warming purposes the rule is the same: only a request that lands in a given colo warms that colo's Workers Cache.

Warming Cloudflare properly

The requirements follow directly from the architecture:

1. Geographic distribution. Requests must enter Cloudflare's network in many regions. In practice that means egress through proxies or agents in dozens of countries — each request then warms the colo that anycast assigns to that region.
2. Browser-shaped requests. Send Accept-Encoding: gzip, br and download the full body. Cloudflare caches compressed variants, and interrupted downloads may not be cached.
3. Bot-protection allowance. Super Bot Fight Mode will challenge datacenter-IP traffic. A WAF skip rule keyed on a secret header solves this cleanly (never allow-list by IP — pools change).
4. Verification via cf-cache-status. MISS on the first pass, HIT on the second. If the second pass still says MISS, your responses aren't cacheable — check Cache-Control and cookies before blaming the warmer.
5. Rhythm matched to TTLs. Warm at roughly half your edge TTL, and re-warm right after every deploy or purge.

What coverage looks like in practice

You don't need a proxy in all 300+ cities — anycast concentrates traffic. From our own measurements: requests through proxies in 42 countries reach about 39 distinct Cloudflare colos directly per pass. Tiered Cache then extends the effect: the upper-tier hubs that serve the remaining locations are warmed as a side effect, so even colos never hit directly stop travelling to the origin.

Checklist

• Enable Tiered Cache (free, one toggle).
• Make your HTML cacheable at the edge (Cache Rule or Cloudflare-CDN-Cache-Control) with purge-on-publish for freshness.
• Warm from many regions, on a schedule, plus after deploys.
• Watch cf-cache-status per colo, not just globally.