Understanding HTTP Headers
In UNIX based systems you can use "curl -I -X GET [url]" to check your file headers. (CDN servers require making a GET request to initiate caching)
curl -I -X GET https://www.cdn77.com/_next/static/css/05de4488a1724d78544e.css
HTTP/2 200 date: Thu, 04 Mar 2021 09:30:33 GMT content-type: text/css; charset=UTF-8 content-length: 62827 alt-svc: quic="22.214.171.124:443"; ma=2592000; v="44,43,39" cache-control: max-age=31536000 last-modified: Wed, 03 Mar 2021 11:09:13 GMT etag: W/"f56b-177f7c70ba8" vary: Accept-Encoding expires: Thu, 03 Mar 2022 11:14:45 GMT server: CDN77-Turbo strict-transport-security: max-age=31536000 x-77-nzt: AbmYQRYIvKvvFDkBAA== x-77-nzt-ray: 0bO89u0QJdU= x-cache: MISS x-77-cache: MISS x-77-pop: pragueCZ accept-ranges: bytes
That means https://www.cdn77.com/_next/static/css/05de4488a1724d78544e.css isn't cached, because of the "X-Cache: MISS" value.
If you repeat the command and the result will change into the following:
x-cache: HIT x-age: 10 x-77-cache: HIT x-77-pop: pragueCZ
However, if you see "X-Cache: MISS" after several tests, it means the file will not be cached in the CDN PoP at all.
Here are few example headers which restrict cache settings:
Cache-Control: max-age=600 - the file will be cached for 600 seconds
Cache-Control: no-cache or Cache-Control: max-age=0 - the file will never be cached in our CDN PoP
Are you not sure how to set correct cache-control headers? Check our guide.