In Drupal, if you want to let your published node appear in search results, you need to re-index the search first (Administration->Configuration->Search Settings). And the Drupal cron job file (cron.php) will be executed to re-index the site at a specific time on every minute, every hour or every day, etc.
But recently I'm building a project outsourcing site, I need the newly posted project can be searched by other users immediately after it's published. I searched on Google and Drupal for a while, finally I found this module: Auto-Index.
This module will automatically re-index the nodes every time a new node is created or an existing node is edited. And there is no more configuration needed after installing.