Use octopus with a master DB with some slaves, and sharded some user DBs

company.rb

# class CreateCompanies < ActiveRecord::Migration
#   def change
#     create_table :companies do |t|
#       t.string :name
#
#       t.timestamps null: false
#     end
#   end
# end

class Company < ActiveRecord::Base
  replicated_model()
end

# > Company.count
#    (0.6ms)  SELECT COUNT(*) FROM "cards"
# => 0
# > Company.using(slave_group: :master_slaves).count
# [Shard: master01]   (0.9ms)  SELECT COUNT(*) FROM "companies"
# => 0

shards.yml

default: &default
  adapter: sqlite3
  pool: 5
  timeout: 5000

octopus:
  replicated: true
  fully_replicated: false

  environments:
    - development

  development:
    master_slaves:
      master01:
        <<: *default
        database: db/development_master01.sqlite3
      master02:
        <<: *default
        database: db/development_master02.sqlite3

    user_shards:
      user01:
        <<: *default
        database: db/development_user01.sqlite3
      user02:
        <<: *default
        database: db/development_user02.sqlite3

user.rb

# class CreateUsers < ActiveRecord::Migration
#   using_group(:user_shards)
#
#   def change
#     create_table :users do |t|
#       t.string :name
#
#       t.timestamps null: false
#     end
#   end
# end

class User < ActiveRecord::Base
end

# > User.count
# ActiveRecord::StatementInvalid: Could not find table 'users'
# from /Users/user/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/sqlite3_adapter.rb:511:in `table_structure'
# > User.using(:user01).count
# [Shard: user01]   (0.6ms)  SELECT COUNT(*) FROM "users"
# => 0