Problem/Motivation
Core provides a "Browser and proxy cache maximum age" setting that is used to set the Cache-Control header:
Cache-Control: max-age=60, public
When using a reverse proxy like Varnish, this header applies to both the reverse proxy and the browser (unless the reverse proxy has some logic to remove the header before it reaches the browser).
Our use case is this:
- We want a low max age for the browser (because we have no way to invalidate the browser cache)
- We want a high max age for the reverse proxy (because we can invalidate this cache with cache tags)
This is possible with the s-maxage directive:
Cache-Control: max-age=60, public, s-maxage=31536000
When both max-age and s-maxage are present, s-maxage applies to shared cache and max-age applies to browsers.
Steps to reproduce
Set cache.page.max_age to a high value like a year. (The interface does not let you do that right now: #3086787: Do not use select list for setting "cache maximum age" option)
Every cacheable response is cached for a very long time by both the reverse proxy and browsers.
Proposed resolution
We could introduce a new "Proxy cache maximum age" setting that would be used to set the s-maxage directive.
I think we should handle these scenarios:
Both max ages are 0:Cache-Control: must-revalidate, no-cache, private
Both max ages are set:Cache-Control: max-age=60, public, s-maxage=31536000
Only max-age is set:Cache-Control: max-age=60, public
Only s-maxage is set:Cache-Control: max-age=0, must-revalidate, public, s-maxage=600
