Is it possible to store the alembic connect string outside of alembic.ini?

I had the very same problem yesterday and found a following solution to work. I do the following in alembic/env.py:

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# this will overwrite the ini-file sqlalchemy.url path
# with the path given in the config of the main code
import config as ems_config
config.set_main_option('sqlalchemy.url', ems_config.config.get('sql', 'database'))

ems_config is an external module that holds my configuration data.

config.set_main_option(...) essentially overwrites the sqlalchemy.url key in the [alembic] section of the alembic.ini file. In my configuration I simply leave it black.

The simplest thing I could come up with to avoid commiting my user/pass was to a) add in interpolation strings to the alembic.ini file, and b) set these interpolation values in env.py

alembic.ini

sqlalchemy.url = postgresql://%(DB_USER)s:%(DB_PASS)[email protected]/nozzle-website

env.py

import os

from logging.config import fileConfig

from sqlalchemy import engine_from_config
from sqlalchemy import pool

from alembic import context

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# here we allow ourselves to pass interpolation vars to alembic.ini
# fron the host env
section = config.config_ini_section
config.set_section_option(section, "DB_USER", os.environ.get("DB_USER"))
config.set_section_option(section, "DB_PASS", os.environ.get("DB_PASS"))

...

Alembic documentation suggests using create_engine with the database URL (instead of modifying sqlalchemy.url in code).

Also you should modify run_migrations_offline to use the new URL. Allan Simon has an example on his blog, but in summary, modify env.py to:

1. Provide a shared function to get the URL somehow (here it comes from the command line):

   def get_url():
       url = context.get_x_argument(as_dictionary=True).get('url')
       assert url, "Database URL must be specified on command line with -x url=<DB_URL>"
       return url
   

2. Use the URL in offline mode:

   def run_migrations_offline():
       ...
       url = get_url()
       context.configure(
           url=url, target_metadata=target_metadata, literal_binds=True)
       ...
   

3. Use the URL in online mode by using create_engine instead of engine_from_config:

   def run_migrations_online():
       ...
       connectable = create_engine(get_url())
       with connectable.connect() as connection:
       ...