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 (1.3.10), 204, 206, 301, 302, 303, 304, 307 (1.1.16, 1.0.13), or 308 (1.13.0). Parameter value can contain variables.

There could be several add_header directives. These directives are inherited from the previous configuration level if and only if there are no add_header directives defined on the current level. Inheritance rules can be redefined with the add_header_inherit directive (1.29.3).

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

add_header_inherit on;

Allows altering inheritance rules for the values specified in the add_header directives. By default, the standard inheritance model is used.

The merge parameter enables appending values from the previous level to the values defined at the current level.

The off parameter cancels inheritance of the values from the previous configuration level.

The inheritance rules themselves are inherited in a standard way. For example, add_header_inherit merge; specified at the top level will be inherited in all nested levels recursively unless redefined later.

Adds the specified field to the end of a response provided that the response code equals 200, 201, 206, 301, 302, 303, 307, or 308. Parameter value can contain variables.

There could be several add_trailer directives. These directives are inherited from the previous configuration level if and only if there are no add_trailer directives defined on the current level. Inheritance rules can be redefined with the add_trailer_inherit directive (1.29.3).

If the always parameter is specified the specified field will be added regardless of the response code.

add_trailer_inherit on;

Allows altering inheritance rules for the values specified in the add_trailer directives. By default, the standard inheritance model is used.

The merge parameter enables appending values from the previous level to the values defined at the current level.

The off parameter cancels inheritance of the values from the previous configuration level.

The inheritance rules themselves are inherited in a standard way. For example, add_trailer_inherit merge; specified at the top level will be inherited in all nested levels recursively unless redefined later.

expires off;

Enables or disables adding or modifying the “Expires” and “Cache-Control” response header fields provided that the response code equals 200, 201 (1.3.10), 204, 206, 301, 302, 303, 304, 307 (1.1.16, 1.0.13), or 308 (1.13.0). 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 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 epoch parameter sets “Expires” to the value “Thu, 01 Jan 1970 00:00:01 GMT”, and “Cache-Control” to “no-cache”.

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;