Modify the maximum cache age

For most responses with an HTTP Status Code of 200, the default cache-control response header value set by VIP’s page cache is max-age=300. This can be set to a custom value on WordPress and Node.js applications.

Routes for site endpoints that rarely change should be set to a higher max-age value, which can improve the cache hit rate.

There is no upper limit to the value set for max-age, but increasing this value is only beneficial within a limited range. By default, cached page content is evicted from the cache according to the max-age TTL  and the GRACE response, which is set to 12 hours for content that is unable to be refreshed.

The page cache also relies on a Least Recently Used (LRU) strategy which will apply if the page cache is low in memory. As a result, setting max-age to a  value beyond a certain range (e.g. > 24 hours) can result in content that is requested less often to occupy valuable space in the page cache, which can lead to more frequent page cache evictions.

Caching for static assets of WordPress and Node.js environments has a different set of default behaviors.

add_action( 'wp', 'my_cache_maxage' );
/**
 * Hooks the wp action to insert some cache control
 * max-age headers.
 *
 * @param Object wp The WP object, passed by reference
 * @return void
 */
function my_cache_maxage( $wp ) {
    if ( is_feed() ) {
        // Set the max age for feeds to 10 minutes.
        if ( ! is_user_logged_in() ) {
            header( 'Cache-Control: max-age=' . ( 10 * MINUTE_IN_SECONDS ) );         
        }
    }
}

const express = require( 'express' );

const app = express();

app.get( '/', function ( req, res ) {
  res
    .set( 'cache-control', 'max-age=3600' )
    .send( 'This response will be cached for 1 hour (3600 seconds)' );
});