Mastering Multi Tenant setup with rails part 1

Multi-tenancy is a software design where a single instance of a software application serves multiple customers or tenants (individual users or organizations). In a multi-tenant architecture, each tenant’s data and configuration are logically isolated from one another, providing a sense of individuality and privacy while sharing the same underlying infrastructure, codebase, and application instance.

Single Tenant application

In a single-tenant application, each hosted instance has its dedicated database. Upon addition of a new organization that requires segregated data, a new application is hosted with a different database.

Multi Tenant Application types

1. Single Database shared rows
   • Each table in database will contain an additional row known as tenant_id.
   • Whenever data is stored and retrieved from table this coloumn will be used to get/store the data.

   • Only the data that belongs to a specific customer/tenant will be fetched.

     
2. Single Database shared schema
   • For each tenant a different table will be maintained in same database.

   • Data will be segregated table wise.

     
3. Dedicated Database for Each Tenant

   • For each tenant a new database schema will be maintained, it can be termed as shard.

     

In this blog post, we’ll take an in-depth look at the third approach, where we opt to manage separate databases for each tenant. To demonstrate this, we’ll walk through the process of creating a basic Rails blog application from the ground up.

Goal

1. Setting up a multi-tenant application in development mode.
2. dynamically switching databases according to the requesting host name.

What features rails 6 brings in

Rails 6 introduced the multiple database setup with following features -

1. Multiple writer databases and a replica for each.
2. Automatic connection switching for the model you’re working with.
3. Automatic swapping between the writer and replica depending on the HTTP verb and recent writes.
4. Rails tasks for creating, dropping, migrating, and interacting with the multiple databases.

Setup

Create new rails app

• rails new multi_db_blog
• update gemfile to use mysql2 instead of sqlite3

Setup databases

1. In database.yml file update the database with name.

development:
  app1:
    adapter: mysql2
    encoding: utf8
    reconnect: false
    database: app1_development
    pool: 5
    username:
    password:
    socket: /tmp/mysql.sock
    host: 127.0.0.1
  app2:
    adapter: mysql2
    encoding: utf8
    reconnect: false
    database: app2_development
    pool: 5
    username:
    password:
    socket: /tmp/mysql.sock
    host: 127.0.0.1

2. bin/rake db:create create databases for both the tenants.
3. You have the option to execute specific rake commands for each database. For instance, you can create the app1 database using the command: bin/rake db:create:app1

Generate Models and Controller

1. Model

   bin/rails generate model Article title:string body:text

2. Run migrations

   bin/rake db:migrate

3. Controller

   bin/rails generate controller Articles index --skip-routes

4. update routes.rb file.

root "articles#index"
resources :articles
    

Complete the Articles Controller, Model and respective views by following This Guide

Start App

1. Run bin/rails s to start the server.
2. By default rails will connect to db1 now.
3. This will act as a default database for the current application.

Running up both databases simaltaneously

Install nginx & paste the following code in nginx.conf file.

http {
  server {
   listen 3000;
   server_name localhost;

   location / {
        proxy_pass http://127.0.0.1:3000; # Rails app running on port 3000
        proxy_set_header Host $host:$server_port;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
  }

  server {
    listen 4000;
    server_name localhost; # Change this to your actual domain if needed

    location / {
        proxy_pass http://127.0.0.1:3000; # Rails app running on port 3000
        proxy_set_header Host $host:$server_port;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
  }
}
events { }

Above nginx configurations listens to port 3000 and 4000 and redirect to rails application running in port 3000.

Additional Rails changes

Since We are using Rails 7 we can use automatic shard swap feature provided by rails. if using rails 6.1 or 6, a middleware can be introduced to automatic switch the tenants depending on request. Visit next section for the details.

Mention list of tenants in a .yml file. You can maintain these records in a separate database as well, for now I will create a settings.yml file.

development:
  tenants:
    app1:
      hosts:
        - localhost:3000
    app2:
      hosts:
        - localhost:4000

update application.rb with following configurations.

Rails.application.configure do
  config.active_record.shard_selector = { lock: true }

  tenants = Rails.application.config_for(:settings)[:tenants]  # maintaining list of tenants with host
  config.active_record.shard_resolver = ->(request) {
    tenants.keys.find { |key| tenants[key][:hosts].include?(request.env['HTTP_HOST']) } || :app1
  }
end

update application_record.rb

   # connects_to shards: {
   #  app1: { writing: :app1 },
   #  app2: { writing: :app2 }
   # }
   # OR

  TENANTS = Rails.application.config_for(:settings)[:tenants]
  connects_to TENANTS.keys.map { |shard| [shard, { writing: shard }] }.to_h

Creating Middleware for automatic shard switching(ignore if using rails 7 or above)

1. Create a middleware named middleware/tenant_selector.rb
2. Add following code

  module Middleware
    class TenantSelector
      def initialize(app, tenants)
        @app = app
        @tenants = tenants
      end

      attr_reader :tenants

      def call(env)
        request = ActionDispatch::Request.new(env)
        tenant = selected_tenant(request)

        set_tenant(tenant) do
          @app.call(env)
        end
      end

      private
      def selected_tenant(request)
        tenants.keys.find { |key| tenants[key][:hosts].include?(request.env['HTTP_HOST']) } || :app1
      end

      def set_tenant(tenant, &block)
        ActiveRecord::Base.connected_to(shard: tenant.to_sym, role: :writing) do
          yield
        end
      end
    end
  end
  

3. Update application.rb file with following changes.

    tenants = Rails.application.config_for(:settings)[:tenants]
    config.app_middleware.use Middleware::TenantSelector, tenants

Final Steps

Follow these final steps to confirm your multi-tenant Rails application is up and running smoothly:

1. Run bin/rails s
2. Access localhost:3000 to connect to db1
3. Access localhost:4000 to connect to db2
4. If you wish to add more databases, simply update the database.yml and settings.yml files

What Next?

In the upcoming series of blog posts, we will delve into the following topics:

1. Maintaining Background Jobs.
2. Running Rake Tasks with Cron Jobs for Multiple Databases.
3. ActiveStorage Data Management with Different Storage Types for Each Tenant.
4. Caching.

Summary

In this blog post we covered creating a multi tenant application from scratch and setting it up in development environment. We were able to automatically switch databases according to type of database.

References

1. Github Code
2. Rails Multi Db introduction