Cache control using a map in Nginx

Google's delightful Lighthouse utility moaned at me about cache-control. For that particular site I use Nginx as a reverse proxy to NodeJS.

Nginx allows us to set a map for filetypes and apply that map to one or more server definitions. To define the map create the following near the top of your configuration file:

map $sent_http_content_type $expires {  
    default                    off;
    text/html                  epoch;
    text/css                   max;
    application/javascript     max;
    ~image/                    max;
}

In the above example, epoch sets the expiry time of all html to 1st January 1970 (which we all know was a Thursday). max on the other hand sets the expiry time to 31st December 2037 (a Friday). Other options off or a specific time.

The last entry, ~image will apply to rule to any content type beginning with image/, for example image/jpeg or image/png.

To apply the map add the following line inside the server block:

server {  
    listen...

    expires $expires;
}