Apartment

Multitenancy for Rails and ActiveRecord

Apartment provides tools to help you deal with multiple tenants in your Rails application. If you need to have certain data sequestered based on account or company, but still allow some data to exist in a common tenant, Apartment can help.

Installation

Rails

Add the following to your Gemfile:

gem 'apartment'

Then generate your Apartment config file using

bundle exec rails generate apartment:install

This will create a config/initializers/apartment.rb initializer file. Configure as needed using the docs below.

That's all you need to set up the Apartment libraries. If you want to switch tenants on a per-user basis, look under "Usage - Switching tenants per request", below.

NOTE: If using postgresl schemas you must use:

• for Rails 3.1.x: Rails ~> 3.1.2, it contains a patch that makes prepared statements work with multiple schemas

Usage

Creating new Tenants

Before you can switch to a new apartment tenant, you will need to create it. Whenever you need to create a new tenant, you can run the following command:

Apartment::Tenant.create('tenant_name')

If you're using the prepend environment config option or you AREN'T using Postgresql Schemas, this will create a tenant in the following format: "#{environment}_tenant_name". In the case of a sqlite database, this will be created in your 'db/' folder. With other databases, the tenant will be created as a new DB within the system.

When you create a new tenant, all migrations will be run against that tenant, so it will be up to date when create returns.

Notes on PostgreSQL

PostgreSQL works slightly differently than other databases when creating a new tenant. If you are using PostgreSQL, Apartment by default will set up a new schema and migrate into there. This provides better performance, and allows Apartment to work on systems like Heroku, which would not allow a full new database to be created.

One can optionally use the full database creation instead if they want, though this is not recommended

Switching Tenants

To switch tenants using Apartment, use the following command:

Apartment::Tenant.switch!('tenant_name')

When switch is called, all requests coming to ActiveRecord will be routed to the tenant you specify (with the exception of excluded models, see below). To return to the 'root' tenant, call switch with no arguments.

Switching Tenants per request

You can have Apartment route to the appropriate tenant by adding some Rack middleware. Apartment can support many different "Elevators" that can take care of this routing to your data.

The initializer above will generate the appropriate code for the Subdomain elevator by default. You can see this in config/initializers/apartment.rb after running that generator. If you're not using the generator, you can specify your elevator below. Note that in this case you will need to require the elevator manually in your application.rb like so

# config/application.rb
require 'apartment/elevators/subdomain' # or 'domain' or 'generic'

Switch on subdomain In house, we use the subdomain elevator, which analyzes the subdomain of the request and switches to a tenant schema of the same name. It can be used like so:

# application.rb
module MyApplication
  class Application < Rails::Application
    config.middleware.use 'Apartment::Elevators::Subdomain'
  end
end

If you want to exclude a domain, for example if you don't want your application to treate www like a subdomain, in an initializer in your application, you can set the following:

# config/initializers/apartment/subdomain_exclusions.rb
Apartment::Elevators::Subdomain.excluded_subdomains = ['www']

This functions much in the same way as Apartment.excluded_models. This example will prevent switching your tenant when the subdomain is www. Handy for subdomains like: "public", "www", and "admin" :)

Switch on domain To switch based on full domain (excluding subdomains ie 'www' and top level domains ie '.com' ) use the following:

# application.rb
module MyApplication
  class Application < Rails::Application
    config.middleware.use 'Apartment::Elevators::Domain'
  end
end

Switch on full host using a hash To switch based on full host with a hash to find corresponding tenant name use the following:

# application.rb
module MyApplication
  class Application < Rails::Application
    config.middleware.use 'Apartment::Elevators::HostHash', {'example.com' => 'example_tenant'}
  end
end

Custom Elevator A Generic Elevator exists that allows you to pass a Proc (or anything that responds to call) to the middleware. This Object will be passed in an ActionDispatch::Request object when called for you to do your magic. Apartment will use the return value of this proc to switch to the appropriate tenant. Use like so:

# application.rb
module MyApplication
  class Application < Rails::Application
    # Obviously not a contrived example
    config.middleware.use 'Apartment::Elevators::Generic', Proc.new { |request| request.host.reverse }
  end
end

Config

The following config options should be set up in a Rails initializer such as:

config/initializers/apartment.rb

To set config options, add this to your initializer:

Apartment.configure do |config|
  # set your options (described below) here
end

Excluding models

If you have some models that should always access the 'public' tenant, you can specify this by configuring Apartment using Apartment.configure. This will yield a config object for you. You can set excluded models like so:

config.excluded_models = ["User", "Company"]        # these models will not be multi-tenanted, but remain in the global (public) namespace

Note that a string representation of the model name is now the standard so that models are properly constantized when reloaded in development

Rails will always access the 'public' tenant when accessing these models, but note that tables will be created in all schemas. This may not be ideal, but its done this way because otherwise rails wouldn't be able to properly generate the schema.rb file.

NOTE - Many-To-Many Excluded Models: Since model exclusions must come from referencing a real ActiveRecord model, has_and_belongs_to_many is NOT supported. In order to achieve a many-to-many relationship for excluded models, you MUST use has_many :through. This way you can reference the join model in the excluded models configuration.

Postgresql Schemas

Providing a Different default_schema

By default, ActiveRecord will use "$user", public as the default schema_search_path. This can be modified if you wish to use a different default schema be setting:

config.default_schema = "some_other_schema"

With that set, all excluded models will use this schema as the table name prefix instead of public and reset on Apartment::Tenant will return to this schema also

Persistent Schemas

Apartment will normally just switch the schema_search_path whole hog to the one passed in. This can lead to problems if you want other schemas to always be searched as well. Enter persistent_schemas. You can configure a list of other schemas that will always remain in the search path, while the default gets swapped out:

config.persistent_schemas = ['some', 'other', 'schemas']

Installing Extensions into Persistent Schemas

Persistent Schemas have numerous useful applications. Hstore, for instance, is a popular storage engine for Postgresql. In order to use extensions such as Hstore, you have to install it to a specific schema and have that always in the schema_search_path.

When using extensions, keep in mind:

• Extensions can only be installed into one schema per database, so we will want to install it into a schema that is always available in the schema_search_path
• The schema and extension need to be created in the database before they are referenced in migrations, database.yml or apartment.
• There does not seem to be a way to create the schema and extension using standard rails migrations.
• Rails db:test:prepare deletes and recreates the database, so it needs to be easy for the extension schema to be recreated here.

1. Ensure the extensions schema is created when the database is created

# lib/tasks/db_enhancements.rake

####### Important information ####################
# This file is used to setup a shared extensions #
# within a dedicated schema. This gives us the   #
# advantage of only needing to enable extensions #
# in one place.                                  #
#                                                #
# This task should be run AFTER db:create but    #
# BEFORE db:migrate.                             #
##################################################


namespace :db do
  desc 'Also create shared_extensions Schema'
  task :extensions => :environment  do
    # Create Schema
    ActiveRecord::Base.connection.execute 'CREATE SCHEMA IF NOT EXISTS shared_extensions;'
    # Enable Hstore
    ActiveRecord::Base.connection.execute 'CREATE EXTENSION IF NOT EXISTS HSTORE SCHEMA shared_extensions;'
    # Enable UUID-OSSP
    ActiveRecord::Base.connection.execute 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp" SCHEMA shared_extensions;'
  end
end

Rake::Task["db:create"].enhance do
  Rake::Task["db:extensions"].invoke
end

Rake::Task["db:test:purge"].enhance do
  Rake::Task["db:extensions"].invoke
end

2. Ensure the schema is in Rails' default connection

Next, your database.yml file must mimic what you've set for your default and persistent schemas in Apartment. When you run migrataions with Rails, it won't know about the extensions schema because Apartment isn't injected into the default connection, it's done on a per-request basis, therefore Rails doesn't know about hstore or uuid-ossp during migrations. To do so, add the following to your database.yml for all environments

# database.yml
...
adapter: postgresql
schema_search_path: "public,shared_extensions"
...

This would be for a config with default_schema set to public and persistent_schemas set to ['shared_extensions']. Note: This only works on Heroku with Rails 4.1+. For apps that use older Rails versions hosted on Heroku, the only way to properly setup is to start with a fresh PostgreSQL instance:

1. Append ?schema_search_path=public,hstore to your DATABASE_URL environment variable, by this you don't have to revise the database.yml file (which is impossible since Heroku regenerates a completely different and immutable database.yml of its own on each deploy)
2. Run heroku pg:psql from your command line
3. And then DROP EXTENSION hstore; (Note: This will drop all columns that use hstore type, so proceed with caution; only do this with a fresh PostgreSQL instance)
4. Next: CREATE SCHEMA IF NOT EXISTS hstore;
5. Finally: CREATE EXTENSION IF NOT EXISTS hstore SCHEMA hstore; and hit enter (\q to exit)

To double check, login to the console of your Heroku app and see if Apartment.connection.default_search_path is public,hstore

3. Ensure the schema is in the apartment config

# config/initializers/apartment.rb
...
config.persistent_schemas = ['shared_extensions']
...

Alternative: Creating schema by default

Another way that we've successfully configured hstore for our applications is to add it into the postgresql template1 database so that every tenant that gets created has it by default.

One caveat with this approach is that it can interfere with other projects in development using the same extensions and template, but not using apartment with this approach.

You can do so using a command like so

psql -U postgres -d template1 -c "CREATE SCHEMA shared_extensions AUTHORIZATION some_username;"
psql -U postgres -d template1 -c "CREATE EXTENSION IF NOT EXISTS hstore SCHEMA shared_extensions;"

The ideal setup would actually be to install hstore into the public schema and leave the public schema in the search_path at all times. We won't be able to do this though until public doesn't also contain the tenanted tables, which is an open issue with no real milestone to be completed. Happy to accept PR's on the matter.

Alternative: Creating new schemas by using raw SQL dumps

Apartment can be forced to use raw SQL dumps insted of schema.rb for creating new schemas. Use this when you are using some extra features in postgres that can't be respresented in schema.rb, like materialized views etc.

This only applies while using postgres adapter and config.use_schemas is set to true. (Note: this option doesn't use db/structure.sql, it creates SQL dump by executing pg_dump)

Enable this option with:

config.use_sql = true

Managing Migrations

In order to migrate all of your tenants (or posgresql schemas) you need to provide a list of dbs to Apartment. You can make this dynamic by providing a Proc object to be called on migrations. This object should yield an array of string representing each tenant name. Example:

# Dynamically get tenant names to migrate
config.tenant_names = lambda{ Customer.pluck(:tenant_name) }

# Use a static list of tenant names for migrate
config.tenant_names = ['tenant1', 'tenant2']

You can then migrate your tenants using the normal rake task:

rake db:migrate

This just invokes Apartment::Tenant.migrate(#{tenant_name}) for each tenant name supplied from Apartment.tenant_names

Note that you can disable the default migrating of all tenants with db:migrate by setting Apartment.db_migrate_tenants = false in your Rakefile. Note this must be done before the rake tasks are loaded. ie. before YourApp::Application.load_tasks is called

Handling Environments

By default, when not using postgresql schemas, Apartment will prepend the environment to the tenant name to ensure there is no conflict between your environments. This is mainly for the benefit of your development and test environments. If you wish to turn this option off in production, you could do something like:

config.prepend_environment = !Rails.env.production?

Delayed::Job

Has been removed... See apartment-sidekiq for a better backgrounding experience

Contributing

• In both spec/dummy/config and spec/config, you will see database.yml.sample files

  • Copy them into the same directory but with the name database.yml
  • Edit them to fit your own settings

• Rake tasks (see the Rakefile) will help you setup your dbs necessary to run tests

• Please issue pull requests to the development branch. All development happens here, master is used for releases

• Ensure that your code is accompanied with tests. No code will be merged without tests

• If you're looking to help, check out the TODO file for some upcoming changes I'd like to implement in Apartment.

License

Apartment is released under the MIT License.