Send a notification or ping in WordPress when a post is created

function.php

<?php 

/**
 * @param   int     $post_id    The ID of the post.
 * @param   WP_Post $post       The post object.
 * @param   bool    $update     True if the post already exists and is being updated
 */
function wpse_post_ping( $post_id, $post, $update ) {
    if ( $post->post_status === 'publish' ) { // Only fire when published
        wp_remote_post(
            'http://example.com/application/notify',
            array(
                // https://codex.wordpress.org/HTTP_API
                'blocking' => false, // If you don't need to know the response, disable blocking for an "async" request
                'body' => array(
                    'post_id' => $post_id,
                    'post'    => json_encode( $post ),
                    'update'  => ( int ) $update,
                    // or whatever
                )
            )
        );
    }   
}

add_action( 'wp_insert_post', 'wpse_post_ping', 10, 3 );