EctoBootMigration

Helper module for Elxiir that can be used to easily ensure that Ecto database was migrated before rest of the application was started.

Rationale

There are many strategies how to deal with this issue, e.g. see https://github.com/bitwalker/distillery/blob/master/docs/Running%20Migrations.md

However, if you have any workers that are relying on the DB schema that are launched upon boot with some methods, such as release post_start hooks you can easily enter race condition. Application may crash as these workers will not find tables or columns they expect and it will happen sooner than the post_start hook script will send the commands to the the application process.

In stateless environments such as Docker it is just sometimes more convenient to perform migration upon boot. This is exactly what this library does.

By default if any migrations have happened it will kill the application. It should be then restarted by any sort of supervisor. It is to avoid cases in which some internal Ecto caches are populated with pre-migration data or some processes are started due to migration process that will later cause issues. This feature can be disabled by passing an argument to the migration-related functions.

Currently it works only with PostgreSQL databases but that will be easy to extend.

Installation

The package can be installed by adding ecto_boot_migration to your list of dependencies in mix.exs:

def deps do
  [{:ecto_boot_migration, "~> 0.1.0"}]
end

Usage

defmodule MyApp do
  use Application

  def start(_type, _args) do
    import Supervisor.Spec, warn: false

    unless EctoBootMigration.migrated?(:my_app) do
      children = [
        supervisor(MyApp.Endpoint, []),
        worker(MyApp.Repo, []),
      ]
      Supervisor.start_link(children, [strategy: :one_for_one, name: MyApp.Supervisor])
    end
  end
end

License

MIT

Author

Marcin Lewandowski