Make WordPress fully comptible with AWS CloudFront, to use as a full-page caching solution.

wp-cloudfront.php

<?php
/**
 * Add Last-Modified and Cache-Control Headers to WP Responses
 */
function wp_cloudfront_filter_headers( $headers ) {

    /*
     * WP already sets Cache-Control headers to avoid caching in the admin.
     */
    if ( is_admin() ) {
        return $headers;
    }

    /*
     * Set Last Modified header to current time
     * Makes it easier to see when the cache was last refreshed
     */
    $modified = date( 'D, j M Y H:i:s e', time() );

    $headers['Last-Modified'] = $modified;

    /*
     * Tell CloudFront not to cache certain responses.
     */
    if ( is_user_logged_in() || is_404() || is_preview() ) {

        $headers['Cache-Control'] = 'no-cache, must-revalidate, max-age=0, proxy-revalidate';

        return $headers;

    }

    /*
     * Set default TTL if not already set
     * If none set CloudFront default is 24 hours
     */
    $ttl = 5 * MINUTE_IN_SECONDS;

    $headers['Cache-Control'] = 'max-age=' . $ttl . ', public';

    return $headers;

}
add_filter( 'wp_headers', 'wp_cloudfront_filter_headers' );