Manual:$wgCdnMaxAge

HTTP proxy (CDN) settings: $wgCdnMaxAge
Cache TTL for the CDN sent as s-maxage (without ESI) or Surrogate-Control (with ESI).
Introduced in version:1.34.0 (Gerrit change 387877; git #f9f8dff4)
Removed in version:still in use
Allowed values:(integer)
Default value:18000

Details edit

Cache timeout for page view caching, will be sent as s-maxage (without ESI) or Surrogate-Control (with ESI). Without ESI, you should strip out s-maxage in the Cdn config. 18000 seconds = 5 hours, more cache hits with 2678400 = 31 days.

This variable was renamed from $wgSquidMaxage in MediaWiki 1.34.