Wordpress - How to modify URI of Featured image before it loaded

I'm using Wordpress 4.5. In an earlier time I used local server to store image (include Featured Image, for example: wp-content/uploads/2016/03/aaabbbccc.jpg). Now I want to move it to AWS S3 Bucket and Cloudfront, and I don't wanna make change in Wordpress's Database and decided to write a plugin to join my cloudfront domain (replace the current domain) to wp-content link every time it retrieve from Database, such as: https://xxyyzzqqaa.cloudfront.net/wp-content/uploads/2016/03/aaabbbccc.jpg.

I use an action hook in my plugin :

add_action( 'the_post', 'change_featured_image' );

Now I don't know what to do next ? Please give me some suggest, thanks in advance !

I found the solution for my problem, it's very easy but I'm newbies with WP so I can't see this.

In your plugin, or where you wanna catch this event when WP load, add this filter:
add_filter( 'post_thumbnail_html', 'change_featured_image' );
With:

• post_thumbnail_html is build-in filter of WP.
• change_featured_image is the function, user define, and run before post_thumbnail_html return its result.

I got some confusing in this function, I don't know the variable to get value. Finally , I found it in WP API document, every vars build-in filter use, you can use too.

Here's the sample code:

function change_featured_image($attr)
{

    global $wpdb;

    $opt = get_option('s3dcs_status');//My value in `wp_options`
    if(empty($opt)) echo $attr;
    else{
        /// Preparing variables
        $pattern = '~(http.*\.)(jpe?g|png|[tg]iff?|svg)~i';
           $m = preg_match_all($pattern,$attro,$matches);
        $il = $matches[0][0];
        $tail = explode("wp-content", $il)[1];
        $s3dcs_remote_link = get_option('s3dcs_cfs3in') . "/wp-content" . $tail;
               echo str_replace($il, $s3dcs_remote_link, $attr) ;
    }   
}

That's all. If you have an issue, please post in here to everyone can know.