Multi-Tenancy

Multi-Tenancy is a widely used architecture to create SaaS applications where the hardware and software resources are shared by the customers (tenants). ABP provides all the base functionalities to create multi tenant applications.

Wikipedia defines the multi-tenancy as like that:

Software Multi-tenancy refers to a software architecture in which a single instance of software runs on a server and serves multiple tenants. A tenant is a group of users who share a common access with specific privileges to the software instance. With a multitenant architecture, a software application is designed to provide every tenant a dedicated share of the instance including its data, configuration, user management, tenant individual functionality and non-functional properties. Multi-tenancy contrasts with multi-instance architectures, where separate software instances operate on behalf of different tenants.

Terminology: Host vs Tenant

There are two main side of a typical SaaS / Multi-tenant application:

A Tenant is a customer of the SaaS application that pays money to use the service.
Host is the company that owns the SaaS application and manages the system.

The Host and the Tenant terms will be used for that purpose in the rest of the document.

Configuration

AbpMultiTenancyOptions: Enable/Disable Multi-Tenancy

AbpMultiTenancyOptions is the main options class to enable/disable the multi-tenancy for your application.

Example: Enable multi-tenancy

Configure<AbpMultiTenancyOptions>(options =>
{
    options.IsEnabled = true;
});

Multi-Tenancy is disabled in the ABP by default. However, it is enabled by default when you create a new solution using the startup template. MultiTenancyConsts class in the solution has a constant to control it in a single place.

Database Architecture

ABP supports all the following approaches to store the tenant data in the database;

Single Database: All tenants are stored in a single database.
Database per Tenant: Every tenant has a separate, dedicated database to store the data related to that tenant.
Hybrid: Some tenants share a single databases while some tenants may have their own databases.

Tenant management module (which comes pre-installed with the startup projects) allows you to set a connection string for any tenant (as optional), so you can achieve any of the approaches.

Usage

Multi-tenancy system is designed to work seamlessly and make your application code multi-tenancy unaware as much as possible.

IMultiTenant

You should implement the IMultiTenant interface for your entities to make them multi-tenancy ready.

Example: A multi-tenant Product entity

using System;
using Volo.Abp.Domain.Entities;
using Volo.Abp.MultiTenancy;

namespace MultiTenancyDemo.Products
{
    public class Product : AggregateRoot<Guid>, IMultiTenant
    {
        public Guid? TenantId { get; set; } //Defined by the IMultiTenant interface

        public string Name { get; set; }

        public float Price { get; set; }
    }
}

IMultiTenant interface just defines a TenantId property. When you implement this interface, ABP automatically filters entities for the current tenant when you query from database. So, you don't need to manually add TenantId condition while performing queries. A tenant can not access to data of another tenant by default.

Why the TenantId Property is Nullable?

IMultiTenant.TenantId is nullable. When it is null that means the entity is owned by the Host side and not owned by a tenant. It is useful when you create a functionality in your system that is both used by the tenant and the host sides.

For example, IdentityUser is an entity defined by the Identity Module. The host and all the tenants have their own users. So, for the host side, users will have a null TenantId while tenant users will have their related TenantId.

Tip: If your entity is tenant-specific and has no meaning in the host side, you can force to not set null for the TenantId in the constructor of your entity.

When to set the TenantId?

ABP automatically sets the TenantId for you when you create a new entity object. It is done in the constructor of the base Entity class (all other base entity and aggregate root classes are derived from the Entity class). The TenantId is set from the current value of the ICurrentTenant.Id property (see the next section).

If you set the TenantId value for a specific entity object, it will override the value set by the base class. If you want to set the TenantId property yourself, we recommend to do it in the constructor of your entity class and do not change (update) it again (Actually, changing it means that you are moving the entity from a tenant to another tenant. If you want that, you need an extra care about the related entities in the database).

ICurrentTenant

ICurrentTenant is the main service to interact with the multi-tenancy infrastructure.

ApplicationService, DomainService, AbpController and some other base classes already has pre-injected CurrentTenant properties. For other type of classes, you can inject the ICurrentTenant into your service.

Tenant Properties

ICurrentTenant defines the following properties;

Id (Guid): Id of the current tenant. Can be null if the current user is a host user or the tenant could not be determined from the request.
Name (string): Name of the current tenant. Can be null if the current user is a host user or the tenant could not be determined from the request.
IsAvailable (bool): Returns true if the Id is not null.

Change the Current Tenant

ABP automatically filters the resources (database, cache...) based on the ICurrentTenant.Id. However, in some cases you may want to perform an operation on behalf of a specific tenant, generally when you are in the host context.

ICurrentTenant.Change method changes the current tenant for a limited scope, so you can safely perform operations for the tenant.

Example: Get product count of a specific tenant

using System;
using System.Threading.Tasks;
using Volo.Abp.Domain.Repositories;
using Volo.Abp.Domain.Services;

namespace MultiTenancyDemo.Products
{
    public class ProductManager : DomainService
    {
        private readonly IRepository<Product, Guid> _productRepository;

        public ProductManager(IRepository<Product, Guid> productRepository)
        {
            _productRepository = productRepository;
        }

        public async Task<long> GetProductCountAsync(Guid? tenantId)
        {
            using (CurrentTenant.Change(tenantId))
            {
                return await _productRepository.GetCountAsync();
            }
        }
    }
}

Change method can be used in a nested way. It restores the CurrentTenant.Id to the previous value after the using statement.
When you use CurrentTenant.Id inside the Change scope, you get the tenantId provided to the Change method. So, the repository also get this tenantId and can filter the database query accordingly.
Use CurrentTenant.Change(null) to change scope to the host context.

Always use the Change method with a using statement like done in this example.

Data Filtering: Disable the Multi-Tenancy Filter

As mentioned before, ABP handles data isolation between tenants using the Data Filtering system. In some cases, you may want to disable it and perform a query on all the data, without filtering for the current tenant.

Example: Get count of products in the database, including all the products of all the tenants.

using System;
using System.Threading.Tasks;
using Volo.Abp.Data;
using Volo.Abp.Domain.Repositories;
using Volo.Abp.Domain.Services;
using Volo.Abp.MultiTenancy;

namespace MultiTenancyDemo.Products
{
    public class ProductManager : DomainService
    {
        private readonly IRepository<Product, Guid> _productRepository;
        private readonly IDataFilter _dataFilter;

        public ProductManager(
            IRepository<Product, Guid> productRepository,
            IDataFilter dataFilter)
        {
            _productRepository = productRepository;
            _dataFilter = dataFilter;
        }

        public async Task<long> GetProductCountAsync()
        {
            using (_dataFilter.Disable<IMultiTenant>())
            {
                return await _productRepository.GetCountAsync();
            }
        }
    }
}

See the Data Filtering document for more.

Note that this approach won't work if your tenants have separate databases since there is no built-in way to query from multiple database in a single database query. You should handle it yourself if you need it.

Infrastructure

Determining the Current Tenant

The first thing for a multi-tenant application is to determine the current tenant on the runtime.

ABP provides an extensible Tenant Resolving system for that purpose. Tenant Resolving system then used in the Multi-Tenancy Middleware to determine the current tenant for the current HTTP request.

Tenant Resolvers

Default Tenant Resolvers

The following resolvers are provided and configured by default;

CurrentUserTenantResolveContributor: Gets the tenant id from claims of the current user, if the current user has logged in. This should always be the first contributor for the security.
QueryStringTenantResolveContributor: Tries to find current tenant id from query string parameters. The parameter name is __tenant by default.
RouteTenantResolveContributor: Tries to find current tenant id from route (URL path). The variable name is __tenant by default. If you defined a route with this variable, then it can determine the current tenant from the route.
HeaderTenantResolveContributor: Tries to find current tenant id from HTTP headers. The header name is __tenant by default.
CookieTenantResolveContributor: Tries to find current tenant id from cookie values. The cookie name is __tenant by default.

Problems with the NGINX

You may have problems with the __tenant in the HTTP Headers if you're using the nginx as the reverse proxy server. Because it doesn't allow to use underscore and some other special characters in the HTTP headers and you may need to manually configure it. See the following documents please: http://nginx.org/en/docs/http/ngx_http_core_module.html#ignore_invalid_headers http://nginx.org/en/docs/http/ngx_http_core_module.html#underscores_in_headers

AbpAspNetCoreMultiTenancyOptions

__tenant parameter name can be changed using AbpAspNetCoreMultiTenancyOptions.

Example:

services.Configure<AbpAspNetCoreMultiTenancyOptions>(options =>
{
    options.TenantKey = "MyTenantKey";
});

If you change the TenantKey, make sure to pass it to CoreModule in the Angular client as follows:

@NgModule({
  imports: [
    CoreModule.forRoot({
      // ...
      tenantKey: 'MyTenantKey'
    }),
  ],
  // ...
})
export class AppModule {}

If you need to access it, you can inject it as follows:

import { Inject } from '@angular/core';
import { TENANT_KEY } from '@abp/ng.core';

class SomeComponent {
    constructor(@Inject(TENANT_KEY) private tenantKey: string) {}
}

However, we don't suggest to change this value since some clients may assume the the __tenant as the parameter name and they might need to manually configure then.

The MultiTenancyMiddlewareErrorPageBuilder is used to handle inactive and non-existent tenants.

It will respond to an error page by default, you can change it if you want, eg: only output the error log and continue ASP NET Core's request pipeline.

Configure<AbpAspNetCoreMultiTenancyOptions>(options =>
{
    options.MultiTenancyMiddlewareErrorPageBuilder = async (context, exception) =>
    {
        // Handle the exception.

        // Return true to stop the pipeline, false to continue.
        return true;
    };
});

Domain/Subdomain Tenant Resolver

In a real application, most of times you will want to determine the current tenant either by subdomain (like mytenant1.mydomain.com) or by the whole domain (like mytenant.com). If so, you can configure the AbpTenantResolveOptions to add the domain tenant resolver.

Example: Add a subdomain resolver

Configure<AbpTenantResolveOptions>(options =>
{
    options.AddDomainTenantResolver("{0}.mydomain.com");
});

{0} is the placeholder to determine the current tenant's unique name.
Add this code to the ConfigureServices method of your module.
This should be done in the Web/API Layer since the URL is a web related stuff.

Openiddict is the default Auth Server in ABP (since v6.0). When you use OpenIddict, you must add this code to the PreConfigure method as well.

// using Volo.Abp.OpenIddict.WildcardDomains

PreConfigure<AbpOpenIddictWildcardDomainOptions>(options => 
{
    options.EnableWildcardDomainSupport = true;
    options.WildcardDomainsFormat.Add("https://{0}.mydomain.com");
});

You must add this code to the Configure method as well.

// using Volo.Abp.MultiTenancy;

Configure<AbpTenantResolveOptions>(options =>
{
    options.AddDomainTenantResolver("{0}.mydomain.com");
});

There is an example that uses the subdomain to determine the current tenant.

If you use a sepereted Auth server, you must install [Owl.TokenWildcardIssuerValidator](https://www.nuget.org/packages/Owl.TokenWildcardIssuerValidator) on the HTTPApi.Host project

dotnet add package Owl.TokenWildcardIssuerValidator

Then fix the options of the .AddJwtBearer block

// using using Owl.TokenWildcardIssuerValidator;

context.Services
    .AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.Authority = configuration["AuthServer:Authority"];
        options.RequireHttpsMetadata = Convert.ToBoolean(configuration["AuthServer:RequireHttpsMetadata"]);
        options.Audience = "ExampleProjectName";
        
        // start of added  block
        options.TokenValidationParameters.IssuerValidator = TokenWildcardIssuerValidator.IssuerValidator;
        options.TokenValidationParameters.ValidIssuers = new[]
        {
            "https://{0}.mydomain.com:44349/" //the port may different
        };
        // end of added  block
    });

Custom Tenant Resolvers

You can add implement your custom tenant resolver and configure the AbpTenantResolveOptions in your module's ConfigureServices method as like below:

Configure<AbpTenantResolveOptions>(options =>
{
    options.TenantResolvers.Add(new MyCustomTenantResolveContributor());
});

MyCustomTenantResolveContributor must inherit from the TenantResolveContributorBase (or implement the ITenantResolveContributor) as shown below:

using System.Threading.Tasks;
using Volo.Abp.MultiTenancy;

namespace MultiTenancyDemo.Web
{
    public class MyCustomTenantResolveContributor : TenantResolveContributorBase
    {
        public override string Name => "Custom";

        public override Task ResolveAsync(ITenantResolveContext context)
        {
            //TODO...
        }
    }
}

A tenant resolver should set context.TenantIdOrName if it can determine it. If not, just leave it as is to allow the next resolver to determine it.
context.ServiceProvider can be used if you need to additional services to resolve from the dependency injection system.

Multi-Tenancy Middleware

Multi-Tenancy middleware is an ASP.NET Core request pipeline middleware that determines the current tenant from the HTTP request and sets the ICurrentTenant properties.

Multi-Tenancy middleware is typically placed just under the authentication middleware (app.UseAuthentication()):

app.UseMultiTenancy();

This middleware is already configured in the startup templates, so you normally don't need to manually add it.

Tenant Store

ITenantStore is used to get the tenant configuration from a data source.

Tenant names are not case-sensitive. ITenantStore will use the NormalizedName parameter to get tenants, You need to use ITenantNormalizer to normalize tenant names.

Tenant Management Module

The tenant management module is included in the startup templates and implements the ITenantStore interface to get the tenants and their configuration from a database. It also provides the necessary functionality and UI to manage the tenants and their connection strings.

Configuration Data Store

If you don't want to use the tenant management module, the DefaultTenantStore is used as the ITenantStore implementation. It gets the tenant configurations from the configuration system (IConfiguration). You can either configure the AbpDefaultTenantStoreOptions options or set it in your appsettings.json file:

Example: Define tenants in appsettings.json

"Tenants": [
    {
      "Id": "446a5211-3d72-4339-9adc-845151f8ada0",
      "Name": "tenant1",
      "NormalizedName": "TENANT1"
    },
    {
      "Id": "25388015-ef1c-4355-9c18-f6b6ddbaf89d",
      "Name": "tenant2",
      "NormalizedName": "TENANT2",
      "ConnectionStrings": {
        "Default": "...tenant2's db connection string here..."
      }
    }
  ]

It is recommended to use the Tenant Management module, which is already pre-configured when you create a new application with the ABP startup templates.

Other Multi-Tenancy Infrastructure

ABP was designed to respect to the multi-tenancy in every aspect and most of the times everything will work as expected.

BLOB Storing, Caching, Data Filtering, Data Seeding, Authorization and all the other services are designed to properly work in a multi-tenant system.

The Tenant Management Module

ABP provides all the the infrastructure to create a multi-tenant application, but doesn't make any assumption about how you manage (create, delete...) your tenants.

The Tenant Management module provides a basic UI to manage your tenants and set their connection strings. It is pre-configured for the application startup template.

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