Caching API on a CDN i.e CloudFlare

This plugin is great, we use it to power a headless NextJS WordPress site and it helped drastically reduce build times by caching repeated requests.

However, i wish there was a way to go a step further with the caching.

We have Cloudflare in-front of our WordPress site, when we cache the requests using their edge network we can get requests down from ~300ms cached to 30ms. Which in turn both helps reduce build times further and load on our origin.

The problem is cache busting here, ideally we’d have a way to hook into the cleanup_deleted_caches function to get all the URLs that were busted to send in a batch to Cloudflare to also bust.

I’ve been playing around with a fork of the plugin to with a wp_rest_cache/deleted_caches action that’s fired when the cron job is run, to provide this.

/**
 * Function called by a cron job to delete flushed or deleted caches from the transients API.
 *
 * @return void
 */
public function cleanup_deleted_caches() {
	global $wpdb;

	/**
	 * How many caches should be cleanup in each run?
	 *
	 * Allows to change the number of cleaned up caches per cron run.
	 *
	 * @since 2020.2.0
	 *
	 * @param int $limit The maximum number of cleaned up caches per cron run.
	 */
	$limit = (int) apply_filters( 'wp_rest_cache/max_cleanup_caches', 1000 );

        // EDIT: select URI & headers
	$sql = "SELECT <code>request_uri</code>, <code>request_headers</code>, <code>cache_key</code>, <code>deleted</code>
							FROM    {$this->db_table_caches}
							WHERE   <code>expiration</code> = %s
							AND     <code>cleaned</code> = %d
							LIMIT   %d";
	// phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
	$caches = $wpdb->get_results( $wpdb->prepare( $sql, date_i18n( 'Y-m-d H:i:s', 1 ), 0, $limit ) );

        // EDIT: add a hook that can be triggered when caches are cleared.
	do_action( 'wp_rest_cache/deleted_caches', $caches );

	if ( $caches ) {
		foreach ( $caches as $cache ) {
			$this->delete_cache( $cache->cache_key, $cache->deleted );
		}
	}

	$sql = "SELECT  COUNT( <code>cache_id</code> ) AS <code>number_of_caches</code>
							FROM    {$this->db_table_caches}
							WHERE   <code>expiration</code> = %s
							AND     <code>cleaned</code> = %d";
	// phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
	$count = $wpdb->get_var( $wpdb->prepare( $sql, date_i18n( 'Y-m-d H:i:s', 1 ), 0 ) );

	if ( $count > 0 ) {
		$this->schedule_cleanup();
	}
}

Using this hook, i then hit the Cloudflare API telling it to purge the URLs that were busted.

I also modified the schedule_cleanup function to not run on a cron job. This is primarily as i wanted the cache busting to be instant rather than after 5 minutes.

I know this is there for performance, but needed a way to trigger this on all the cases that a cache entry could get deleted as outlined here https://www.ads-software.com/support/topic/hook-for-when-cache-is-cleared/

private function schedule_cleanup() {
	$this->cleanup_deleted_caches();
}

Would be potentially nice to have the option to trigger this instantly vs using a cron job.

Finally on top of this i needed to add some headers to tell Cloudflare to cache the resource, i could do this using the hook below.

add_filter(
	'wp_rest_cache/cache_headers',
	function ( $headers ) {

		// Add cache-headers so that Cloudflare can cache the response.
		$headers['Cache-Control'] = 'public, max-age=300, s-maxage=300';
		return $headers;
	},
	10000
);

However, ideally this would be added to the initial request too, the header is only returned in the second request if the request wasn’t already cached. So it requires 2 requests before Cloudflare caches it.

Not sure if you know of a better way to hook this up to a CDN infront? Thanks!

• This topic was modified 2 years, 4 months ago by andrewceharris.