There are definitely downsides to scaling out thousands of tenants - I've been told Heroku supports this, and at a glance I found this doc that says it may cause issues,
https://devcenter.heroku.com/articles/heroku-postgresql#mult... but it really doesn't change whether you're on Heroku or not. At the end of the day it's just about your application structure, how much data you have, how many tables you have etc. Unfortunately the Apartment gem even has these problems, and even its creators have expressed some concern (
https://zeph.co/multitenancy-without-subdomains-rails-5-acts...) about scalability with multiple schemas.
The acts_as_tenant gem might be what you’re looking for:
> This gem was born out of our own need for a fail-safe and out-of-the-way manner to add multi-tenancy to our Rails app through a shared database strategy, that integrates (near) seamless with Rails.
My recommended configuration to achieve this is to simply add a `tenant_id` column (or `customer_id` column, etc) on every object that belongs to a tenant, and backfilling your existing data to have this column set correctly. When a new account signs up, not a lot happens under-the-hood; you can create a row in the main table with the new account, do some initial provisioning for billing and such, and not much else. Being a multi-tenant platform you want to keep the cost really low of signing up new accounts. The easiest way to run a typical SQL query in a distributed system without restrictions is to always access data scoped by the tenant. You can specify both the tenant_id and an object’s own ID for queries in your controller, so the coordinator can locate your data quickly. The tenant_id should always be included, even when you can locate an object using its own object_id.