https://github.com/github/gh-ost

gh-ost is a triggerless online schema migration solution for MySQL. It is testable and provides pausability, dynamic control/reconfiguration, auditing, and many operational perks.
gh-ost produces a light workload on the master throughout the migration, decoupled from the existing workload on the migrated table.

It has been designed, developed in golang, based on years of experience with existing solutions, and changes the paradigm of table migrations.