Departure is an ActiveRecord connection adapter that allows running MySQL online and non-blocking DDL through ActiveRecord::Migration without needing to use a different DSL other than Rails’ migrations DSL.

Source: departurerb/departure: Percona’s pt-online-schema-change runner for ActiveRecord migrations.

Basically, Departure is another take on the problem that SoundCloud’s LHM solves. Aside: apparently Shopify’s fork of LHM is better maintained today, but I haven’t used it directly.

Departure even has support for the DSL from LHM. Nice!