Nginx Variable Cache Time - nginx

Question

I'm currently working with fastcgi_cache and wanted to pass a variable to fastcgi_cache_valid so I could have variable amount of cache time depending on the file. But it seems that it will not accept a variable.
I tried the following:
set $cache_time 15s;
fastcgi_cache_valid 200 ${cache_time};
fastcgi_cache_valid 200 $cache_time;
set $cache_time "15s";
fastcgi_cache_valid 200 ${cache_time};
fastcgi_cache_valid 200 $cache_time;
set $cache_time 15;
fastcgi_cache_valid 200 ${cache_time}s;
fastcgi_cache_valid 200 $cache_time;
But I receieved the following errors:
nginx: [emerg] invalid time value "$cache_time" in /etc/nginx/conf.d/www.com.conf:118
nginx: [emerg] directive "fastcgi_cache_valid" is not terminated by ";" in /etc/nginx/conf.d/www.com.conf:118

Answer 1

fastcgi_cache_valid does not accept variable but there is a work around if you have only two options cached and not-cached.
In this example we want cached.php to return the cached version, and the non-cached version if the url contains params. meaning cached.php will always reaturn the cached version and cached.php?id=1 will always return the non-cached version.
location = /cached.php {
include snippets/fastcgi-php.conf;
fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;
set $disable_cache 1;
if ( $request_uri = "/cached.php" ){
set $disable_cache 0;
}
fastcgi_cache phpcache;
fastcgi_cache_valid 200 1h;
fastcgi_cache_methods GET HEAD;
fastcgi_cache_bypass $disable_cache;
fastcgi_no_cache $disable_cache;
add_header X-Is-Cached "Cache disabled $disable_cache";
}
This the content of cached.php used for test
<?php echo "The time is " . date("h:i:sa")."\n";?>
This is the results if tests using curl
curl --head "http://www.example.com/cached.php"
HTTP/1.1 200 OK
Server: nginx/1.14.0 (Ubuntu)
Date: Thu, 31 Dec 2020 17:07:55 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
X-Fastcgi-Cache: HIT
X-Is-Cached: Cache disabled 0
curl --head "http://www.example.com/cached.php?id=1"
HTTP/1.1 200 OK
Server: nginx/1.14.0 (Ubuntu)
Date: Thu, 31 Dec 2020 17:09:15 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
X-Fastcgi-Cache: BYPASS
X-Is-Cached: Cache disabled 1
X-Is-Cached is used only for debuging and it is not necessary.