Magento 2: One or more indexers are invalid

Question

Accepted Answer

Magento 2 requires full reindex after significant changes:

new store view/website was added
key options in the configuration were changed
added new attribute (search reindex is required)
catalog price rules were changed (price and flat index are required)
etc

After all these changes, Magento 2 require run full reindex for some or even all indexes.

Reindex via a CLI (Command Line Interface)

To run Magento 2 reindex via CLI, just follow this command:

bin/magento indexer:reindex

The output will be:

Design Config Grid index has been rebuilt successfully in 00:00:00
Customer Grid index has been rebuilt successfully in 00:00:00
Product Flat Data index has been rebuilt successfully in 00:00:02
Category Flat Data index has been rebuilt successfully in 00:00:00
Category Products index has been rebuilt successfully in 00:00:00
Product Categories index has been rebuilt successfully in 00:00:00
Product Price index has been rebuilt successfully in 00:00:03
Product EAV index has been rebuilt successfully in 00:00:02
Catalog Rule Product index has been rebuilt successfully in 00:00:02
Catalog Product Rule index has been rebuilt successfully in 00:00:00
Stock index has been rebuilt successfully in 00:00:00

Manual Reindex from the Admin Panel

Also, you can use Improved Asynchronous Re-indexing for run reindex from Magento 2 Admin Panel: