Module ngx_http_headers_module

The ngx_http_headers_module module allows adding the “Expires” and “Cache-Control” header fields, and arbitrary fields, to a response header.

expires    24h;
expires    modified +24h;
expires    @24h;
expires    0;
expires    -1;
expires    epoch;
expires    $expires;
add_header Cache-Control private;

Adds the specified field to a response header provided that the response code equals 200, 201, 204, 206, 301, 302, 303, 304, or 307. A value can contain variables.

There could be several add_header directives. These directives are inherited from the previous level if and only if there are no add_header directives defined on the current level.

If the always parameter is specified (1.7.5), the header field will be added regardless of the response code.

expires off;

Enables or disables adding or modifying the “Expires” and “Cache-Control” response header fields provided that the response code equals 200, 201, 204, 206, 301, 302, 303, 304, or 307. The parameter can be a positive or negative time.

The time in the “Expires” field is computed as a sum of the current time and time specified in the directive. If the modified parameter is used (0.7.0, 0.6.32) then the time is computed as a sum of the file’s modification time and the time specified in the directive.

In addition, it is possible to specify a time of day using the “@” prefix (0.7.9, 0.6.34):

expires @15h30m;

The epoch parameter corresponds to the absolute time “Thu, 01 Jan 1970 00:00:01 GMT”. The contents of the “Cache-Control” field depends on the sign of the specified time:

• time is negative — “Cache-Control: no-cache”.
• time is positive or zero — “Cache-Control: max-age=t”, where t is a time specified in the directive, in seconds.

The max parameter sets “Expires” to the value “Thu, 31 Dec 2037 23:55:55 GMT”, and “Cache-Control” to 10 years.

The off parameter disables adding or modifying the “Expires” and “Cache-Control” response header fields.

The last parameter value can contain variables (1.7.9):

map $sent_http_content_type $expires {
    default         off;
    application/pdf 42d;
    ~image/         max;
}

expires $expires;