Yeah, sorry have been traveling today, my first answer was overly
simplistic because you have the opposite problem of online migrations,
instead of one database version accessed by multiple versions of the code,
you have multiple database versions you want accessed by one version of
code.  I think the idea of running multiple application servers with
different versions of the application, then with routing logic on top that
handles the per tenant routing, is a good one, this depends on how your
application and url structure is organized.

On Sun, Feb 3, 2019, 7:41 PM Sergey V. <[email protected] wrote:

> We have a similar setup (a PostgreSQL schema per tenant), we deal with
> different database versions by running different *code versions* - i.e.
> if you need a new column you release a new code version which knows how to
> deal with the new column. Switching a tenant to that code version runs an
> Alembic migration which adds the column to their schema. Each request is
> routed to a particular code version depending on the tenant's database
> schema.
>
> This way the old code never sees the new database structure and vice versa.
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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-- 
SQLAlchemy - 
The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

To post example code, please provide an MCVE: Minimal, Complete, and Verifiable 
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