Always Online

Always Online keeps your site available when the origin fails: expired pages are served from cache instead of an error page. Cache warming fills the cache ahead of visitors, so more pages have a copy to fall back on. Both are configured on the site’s Always Online page in the admin.

Always Online

When the origin is unreachable, times out or returns a server error, pages in cache keep being served, even after their one-hour lifetime has expired. Each page stays available for the stale period you choose, counted from when it expired. In normal operation pages are still refreshed every hour, so visitors only see older content while the origin is failing.

Always Online is enabled by default for new sites. When your server is down explains exactly what visitors see during an outage.

Stale period

Serve stale for up to sets how long expired pages remain available: 1, 2, 6, 12, 24 or 48 hours. The default is 24 hours.

A longer period covers longer outages, at the cost of possibly serving older content while the origin is down. Since a regularly visited page is refreshed every hour, the period mostly matters for pages visited less often.

What it does not cover

• Pages that are not in cache. A page nobody has requested recently has no copy to serve. Cache warming reduces this gap.
• Requests that bypass the cache, such as logged-in sessions, /wp-admin and checkout pages. They always need the origin.
• Purged or flushed pages. Purges remove stale copies too, so avoid flushing the cache while the origin is down. See How the cache is refreshed.

Origin down alerts

Always Online also runs a health probe against your homepage every 10 seconds. It powers the origin status shown in the admin and the origin down alerts configured under Settings → Alerts, which therefore require Always Online to be enabled. The probe expects a 200 from your homepage: a homepage that redirects causes false alerts.

Cache warming

Cache warming requests your pages through the cache before visitors do, so they are served from memory from the first visit and protected by Always Online.

Running it

• Warm Cache starts a run immediately and shows its progress.
• Auto-warm schedule repeats it every 6, 12, 24 or 48 hours. Scheduled runs start within 30 minutes of being due.
• After a flush: when Always Online is enabled, Flush Cache in the admin starts a warming run automatically.

Which pages are warmed

1. Custom URLs first, one per line, in the order you list them. Use them for important pages that are missing from your sitemap.
2. Your sitemap. Edge Caching looks for /wp-sitemap.xml, /sitemap_index.xml and /sitemap.xml, in that order, and uses the first that lists pages. Sitemap indexes are followed, and only URLs on your site’s domain are kept.

A run warms up to 500 URLs in total. If no sitemap is found, only the homepage is warmed.

Load on your origin

Warming requests one page at a time, with a short pause between pages and a 15-second timeout per page, so it never sends your origin more than one concurrent request. Pages already in cache are answered from memory and cost the origin nothing. Warming requests are sent to the site’s cache over the platform’s internal network, with the user agent Layer7-CacheWarmer/1.0.