Always Online
Always Online keeps your site reachable when your origin goes down. Instead of returning an error, the CDN serves the stale cached copy of a page it last fetched successfully. It is on for every property and needs no configuration.
How it works
When a request would fail at the origin, the CDN checks whether it has a previously cached response for that URL. If it does, it serves that copy and the visitor sees the last-known-good content instead of an error page.
When it kicks in
| Condition | Meaning |
|---|---|
error | The origin could not be reached (connection refused or reset). |
timeout | The origin did not respond in time. |
500 | Internal Server Error. |
502 | Bad Gateway. |
503 | Service Unavailable. |
504 | Gateway Timeout. |
A cached copy that has expired is also served while the edge fetches the new one in the background, so visitors never wait on a refresh.
Responses such as 403, 404 or 429 are passed through as they are: they are usually deliberate answers from your origin, not failures.
What visitors get
A stale copy is marked as such: the X-Cache-Status response header reads STALE (or UPDATING while the edge refreshes it), Age shows how old the copy really is, and the browser is told to keep it for 10 seconds only. When your origin comes back, visitors get the fresh page right away instead of a copy stuck in their browser cache.
Always Online can only serve content it has previously cached. A URL that was never cached — never requested, not cacheable (no cache rule and no cache headers from the origin, or a response that sets a cookie), purged, or not requested for 7 days — has no copy to fall back to, so the failure passes through as an error.
Related
- Browser caching & query strings — how long content stays cached, which determines what's available to serve stale.
- Origin server and Host header — the origin whose failures Always Online absorbs.