When it comes to Drupal and external data, I use Migrate. A lot. Like a lot, lot, lot. Many times this data is being imported over CSV files that are pushed to a server at some defined interval. Usually, the data can be derived directly from the CSV file itself, other times a custom process plugin derives data from other information. Drupal's Migrate system has two steps to check if new data should be imported or skipped. First, you can tell the migration source to track changes for each row. Then, if you are tracking changes, it hashes each row of data to see if it has been changed.
My personal site is now officially migrated onto Drupal 8! I had first attempted a migration of my site back when Drupal 8.0 was released but had a few issues. With Drupal 8.3 it was nearly flawless (maybe even 8.2, but I had put the idea back burner.) I did have some interesting issues to workaround
Missing filter plugins
My migration process was halted and littered with errors due to missing plugins, specifically around my text formats. The culprits were:
Plans were made back in December 2015 to put effort into the ability to support Migrate with Drupal Commerce to speed up adoption of Drupal Commerce 2.0. Commerce Migrate for Drupal 8 will provide migrations from Drupal Commerce 1.x, Ubercart for D6, and Ubercart for D7. Ideally, this module will also support other vendors, such as Magento and WooCommerce.
Right now two of the most popular open source content management systems are WordPress and Drupal. WordPress is very simplistic and easy to roll out, which is why there is nearly 80,000,000 websites using WordPress. Then you have Drupal which is a more robust content management system that needs a little bit more love to get things moving.