如何设置FlaskSQLAlchemy以在启动时优雅地管理PostgreSQL不可用性

Question

我有一个flask API，一切正常，一切都已固定，以便进行本地测试，这是flaskinit.py：

import os
from os.path import join, dirname

import cloudinary
import sentry_sdk
from sentry_sdk.integrations.flask import FlaskIntegration
from dotenv import load_dotenv
from flask import Flask
from flask_cors import CORS
from flask_marshmallow import Marshmallow
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
from flask_limiter import Limiter
from flask_limiter.util import get_remote_address

cors = CORS()
marsh = Marshmallow()
db = SQLAlchemy()
migrate = Migrate()
limiter = Limiter(key_func=get_remote_address)

from deblurrer.api import api_bp


def create_app(config='flask_config.Production'):
    """
    Init core application.

    Args:
        config: can be import to object or the object itself

    Returns:
        Application instance
    """
    # Load .env vars
    dotenv_path = join(dirname(dirname(__file__)), '.env')
    load_dotenv(dotenv_path)

    # Setup default production config
    app = Flask('deblurrer', instance_relative_config=True)
    app.config.from_object(config)

    # Sentry config
    sentry_sdk.init(
        dsn=os.environ.get('SENTRY_DNS'),
        integrations=[FlaskIntegration()]
    )

    # Init Cloudinary credentials
    cloudinary.config(
        cloud_name = os.environ.get('CLOUDINARY_CLOUD_NAME'),
        api_key = os.environ.get('CLOUDINARY_API_KEY'),
        api_secret = os.environ.get('CLOUDINARY_API_SECRET'),
    )

    # Init Plugins
    cors.init_app(app)
    marsh.init_app(app)
    db.init_app(app)
    migrate.init_app(app, db)
    limiter.init_app(app)

    with app.app_context():
        app.register_blueprint(api_bp, url_prefix='/api')

        # Create tables for models
        db.create_all()

        return app

当我执行docker-compose up时，PostgreSQL容器不会在flaskapi容器之前启动，这是正常的和预期的。建议准备API，以便在任何时候（包括开始时间）优雅地管理数据库不可用性

我的问题是，我如何在我的烧瓶应用程序上做到这一点？在初始化SQLAlchemy时，似乎必须在init.py上执行此操作，但我不知道如何进行，我尝试了一些研究，但没有明显的结果，您能帮助我吗

谢谢

Answer 1

继续努力

# Connect to database
tries = 5
while tries > 0:
    try:
        db.create_all()
        tries = 0
    except:
        tries += -1
        print('Failed to connect to database. Waiting and then trying again (try countdown: %s)' % tries)
        sleep(10)  # Wait a bit until database is loaded