Database and Migrations

The bundled Postgres, writing a migration, and running it.

The database is Postgres, and Elements bundles it. There is nothing to install. A per-machine elements-machine daemon runs a single Postgres cluster shared by all your projects; it is created automatically, kept healthy, and listens on loopback port 5433 (not the usual 5432, so it never collides with a Postgres you already run). Data lives under ~/elements/db in development.

On the first build, the project connects to the daemon, the cluster is ensured ready, and your project's app database and test database are created automatically. The names derive from the project directory (MyApp → my_app and my_app_test), or from database.name in config.jsoc.

Migrations are SQL files under app/migrations/, and applying them is part of the build loop. Save a migration and Elements applies it, to the test database first, then the app database. In development you can edit an applied migration and Elements rolls it back and replays it. On a deploy machine a migration runs exactly once and is frozen thereafter.

To point at a remote or hosted Postgres instead of the bundled cluster, set DB_HOST (and the other DB_* values) in the active environment. Full topics: elements man database, elements man migrations.