Magento 2: One or more indexers are invalid

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: