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Bleib

About

With bleib, your Rails application gains two new rake tasks:

  • bleib:wait_for_database - waits until the database is running and the configured user can access it
  • bleib:wait_for_migrations - performs bleib:wait_for_database, then waits until all migrations are up

Bleib knows about the Apartment gem - if your project includes it, it will also check migrations on tenants. Likewise, it knows about the Wagons gem and checks for migrations in all known wagons.

This was built to be used in kubernetes/OpenShift deployments without a zero downtime approach.

It allows you to kubectl apply your multi-Rails-pod configuration and delegate migrations to either a Job or one of the Pods. Using bleib initContainers, dependent Rails Pods (say job workers or multiple replicas) can wait for migrations or DB redeployments to finish.

How to

  • Add the gem to your application: gem 'bleib'
  • Build your application image.
  • Add an initContainer that's based on your application image to your application Pod.
  • Set the command of the initContainer to rake bleib:wait_for_migrations.
  • Add some way to migrate the database so that the waiting actually pays off at some point.
  • The migrations can be run after rake bleib:wait_for_database sees a connection.

Configuration

Bleib's behaviour is configured via the environment:

Environment variable Default value Description
BLEIB_CHECK_DATABASE_INTERVAL 5 Seconds to wait between database readiness checks
BLEIB_CHECK_MIGRATIONS_INTERVAL 5 Seconds to wait between migration readiness checks
BLEIB_DATABASE_YML_PATH config/database.yml Path to database.yml. Bleib needs this to perform database readiness checks without booting the whole rails environment.
BLEIB_LOG_LEVEL info Set this to debug to investigate why bleib is hanging.
BLEIB_DEFAULT_TENANT public Name of well-known always existing Tenant. This depends on the strategy you use with Apartment and your RDBMS.

Caveats

  • Handles the postgresql, postgis and mysql2 database adapters. It's simple to add further adapters, see Bleib::Database#database_down_exception? and Bleib::Configuration#check!

Testing

Done by hand so far.

If I had a magic wand, I'd do integration tests of Bleib::Database and Bleib::Migrations against a database container in various states (up, down, preloaded with dumps of different migration states).

ToDo (patches welcome)

  • add a basic rspec skeleton
  • add (mocked) specs for Bleib::Migrations
  • add (mocked) specs for Bleib::Database
  • add integration test for Bleib::Database
  • add integration test for Bleib::Migrations
  • add specs for Bleib::Configuration