You can develop multi tenant application very easily with Ruby on Rails

This article describe how you can use the tenant_id  in different ways when you build the multi-tenant application

You can use the gem called apartment

Multitenancy Crash Course:
Multitenancy with the Apartment gem

If you would like to learn more about Multi Tenancy Architecture you can visit this tutorial

Three Database Architectures for a Multi-Tenant Rails-Based SaaS App