= Nginx Client Caching =

'''`nginx(8)`''' has a simplified API to managing the headers that affect client-side caching of resources.

<<TableOfContents>>

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== Unit Measurements ==

In `nginx(8)` configuration files, time is measured in...

 * milliseconds (`ms` suffix)
 * seconds (`s` suffix)
 * minutes (`m` suffix)
 * hours (`h` suffix)
 * days (`d` suffix)
 * weeks (`w` suffix)
 * months (`M` suffix) (note: always equal to 30 days)
 * years (`y` suffix) (note: always equal to 365 days)

In that case that a plain integer is provided (i.e. no suffix), it is treated as a measurement in seconds.

Units can be combined as long as they are in order from greatest to least significance. A space between units is optional. For example, `2h30m` and `2h 30m` may be more readable than `150m`.

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== Enabling ==

To cause a client device to cache all web resources for the next 30 days, try the following:

{{{
location / {
  expires 30d;
}
}}}

The `expires` directive sets the `Expires` and `Cache-Control` headers. The expiry will happen at current time plus the parameter passed on the `expires` directive. This can either be an integer (e.g. `expires 

This is more effective when applied to a subset of resources, such as images or CSS stylesheets. Simply adjust the [[Nginx/Location|location block]] that the `expires` directive is used in.

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== Disabling ==

Consider one of these two options:

{{{
location / {
  expires off;
}
}}}

The `off` keyword disables adding `Expires` and `Cache-Control` headers. This is not necessarily the same as disabling client-side caching though.

{{{
location / {
  expires -1;
}
}}}

Passing a negative value sets the expiry to a past time, so that all resources will always be considered expired. The `Cache-Control` header will also be automatically set to `Cache-Control: no-cache`.

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== Tips ==

Take into account how the `Cache-Control` header will interact with [[Nginx/Compression#Gzip_Proxied|compression]].

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== See also ==

[[https://nginx.org/en/docs/http/ngx_http_headers_module.html|Module ngx_http_headers_module documentation]]
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