run_after_db.py

#!/usr/local/bin/python
"""Bootstraps the FastAPI application, first waiting for the Postgres
database to be up and running.
"""
import os
import time
import argparse

from sqlalchemy import text as sa_text, create_engine
from sqlalchemy.exc import OperationalError

MAX_RETRIES = 120

parser = argparse.ArgumentParser(description=
    'Wait for the database to be responsive and then runs a command.')
parser.add_argument(
    'command_line',
    nargs='+',
    help=('The command to run after the database is online. '
        'Please encase the command in quotes.'))
args = parser.parse_args()
command = ' '.join(args.command_line) # pylint: disable=invalid-name

engine = create_engine(os.environ['SQLALCHEMY_DATABASE_URL'])

for _ in range(MAX_RETRIES):
    try:
        with engine.connect() as connection:
            connection.execute(sa_text("select 'TEST';"))
            print('Postgres database found.')
        break
    except OperationalError as e:
        print('Postgres database unavailable, waiting...')
    time.sleep(1)

print('Executing command: ', command)
os.system(command)