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Magento 2 allows configurable products to be imported through the CMS.
Unlike Magento 1 where Magmi generally did all the hard work when it came to importing and updating Configurable Products the built-in system in M2 allows you do do it without any additional plugins/code.
The folks at Lexiconn seem to have cracked it: Magento 2 – Import Configurable Products
Be sure that before you begin looking at your CSV that all the prerequisites have been put in place - setting up the attributes, attribute sets and categories.