[TS-886] Grace mode supported, very useful for slow origins

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Done
• Component/s: Cache, Core, HTTP
• Labels: backgound grace stale

Environment

N/A

• Assignee: Unassigned
• Reporter: Ricky Chan
• Created: 24/Jul/11 20:13
• Updated: 19/Jan/14 15:29
• Resolved: 01/Nov/13 22:32

Description

Varnish has long supported a mode called "grace mode" see https://www.varnish-cache.org/docs/trunk/tutorial/handling_misbehaving_servers.html.

This is useful in cases where the origin server is slow at generating data, and you can configure it to serve stale content while a backend job is fetching the object.

I would suggest this feature be enhanced to include support for.

• url regex match to apply grace to.
• override must-revalidate so that grace can be used (I know this violates the RFC, but a cache admin can optionally do this on a per origin/url basis).

For example I have some origins which take between 5 to 20 seconds to generate content and this is handy in these known cases.