Building a Multi-Tenant SaaS App with ASP.NET Core

Multi-Tenancy Strategies

There are three main approaches: separate databases, shared database with schema, and shared schema with tenant ID. Each has trade-offs.

Tenant Resolution Middleware

public class TenantMiddleware(RequestDelegate next)
{
    public async Task InvokeAsync(HttpContext ctx, ITenantService tenants)
    {
        var host = ctx.Request.Host.Host;
        var tenant = await tenants.ResolveAsync(host);
        ctx.Items["Tenant"] = tenant;
        await next(ctx);
    }
}

Scoped DbContext per Tenant

services.AddDbContext<AppDbContext>((sp, opts) =>
{
    var tenant = sp.GetRequiredService<ITenantContext>();
    opts.UseSqlServer(tenant.ConnectionString);
});

Conclusion

Start with shared schema + tenant ID for simplicity. Migrate to separate databases only when isolation requirements demand it.