Manual:$wgSquidMaxage

HTTP proxy (CDN) settings: $wgSquidMaxage
Cache timeout for the squid.
Introduced in version:1.2.0
Deprecated in version:1.34.0 (Gerrit change 387877; git #f9f8dff4)
Removed in version:1.35.0 (Gerrit change 579755; git #e8d9d68b)
Allowed values:(integer)
Default value:18000

Details

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