Use dockered databases for rails development

docker_datasource.rb

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# lives in config/initializers/docker_datasource.rb
# requires:
#   gem 'docker-api', '1.32.1'
#
# gem 'docker-api', '1.32.1'
require 'docker'

# set this to something other than 'postgres'
DB_NAME='myProject'

def try_psql(container)
    ret = container.exec(["psql", "-U", "postgres", "-c", "SELECT 1"], wait: 10, tty: true)
    raise 'No PSQL SELECT 1' unless ret[2] == 0
end

def retry_psql(container)
        tries ||= 10
        print "."
        try_psql(container)
    rescue Exception => e
        sleep 1
        retry unless (tries -= 1).zero?
    else
        puts " success (attempt #{11-tries}/10)"
        # just hold off for a couple of seconds as the docker init process brings the database up and down a few times at startup.
        sleep 2
end

if( ENV['DOCKER_DB'] )
    container = Docker::Container.create( 'Image' => 'postgres:latest', 'ExposedPorts' => { '5432/tcp' => {} },
  'HostConfig' => {
    'PortBindings' => {
      '5432/tcp' => [{}]
    }
  }, 'Env' => [ 'POSTGRES_DB=' + DB_NAME ]  )
    
    container.start
    
    at_exit do
        puts "destroying docker container: #{container.id}"
        container.delete(:force => true)
    end
    
    puts "started docker container: #{container.id}"
    print "waiting for database: "
    retry_psql container

    json = container.json
    pg_port = json['NetworkSettings']['Ports']["5432/tcp"][0]["HostPort"]

    ENV['DATABASE_URL'] = "postgresql://postgres@localhost:#{pg_port}/" + DB_NAME + "?pool=5"

    puts "db:migrate"
    if(true || Rails.env != "test")
        migrations_path = Rails.root.join("db/migrate")
        ActiveRecord::Migrator.migrate(migrations_path)

        migrations = ActiveRecord::Migrator.migrations(migrations_path)
        migrator = ActiveRecord::Migrator.new(:up, migrations)
        puts "HERE"
        puts migrator.pending_migrations
        puts "THERE"
    end
end