Bleib

About

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

wait_for_database - waits until the database is running and the configured user can access it
wait_for_migrations - performs 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.

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 wait_for_migrations.

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 postresql, 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.