Python Flask SQLAlchemy 容器无法连接到 Z62A004B95946BB73AZ 容器

Question

I am unable to connect to my MySQL database from Flask application.

I am learning to build web application with Python Flask from this tutorial but tried modifying some elements of it for experimenting with Docker. Even without using docker-compose, I was unable to connect to the database from the web application.

Let me first give the error traceback in the application log (flask_test container):

[2021-12-20 18:13:18 +0000] [1] [INFO] Starting gunicorn 20.1.0

[2021-12-20 18:13:18 +0000] [1] [INFO] Listening at: http://0.0.0.0:5000 (1)

[2021-12-20 18:13:18 +0000] [1] [INFO] Using worker: sync

[2021-12-20 18:13:18 +0000] [8] [INFO] Booting worker with pid: 8

[2021-12-20 18:13:19,105] INFO in __init__: Microblog startup

[2021-12-20 18:14:19,239] ERROR in app: Exception on /auth/register [POST]

Traceback (most recent call last):

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/connection.py", line 174, in _new_conn

    conn = connection.create_connection(

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/util/connection.py", line 96, in create_connection

    raise err

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/util/connection.py", line 86, in create_connection

    sock.connect(sa)

ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:


Traceback (most recent call last):

  File "/home/flasktest/venv/lib/python3.10/site-packages/elasticsearch/connection/http_urllib3.py", line 255, in perform_request

    response = self.pool.urlopen(

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/connectionpool.py", line 755, in urlopen

    retries = retries.increment(

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/util/retry.py", line 507, in increment

    raise six.reraise(type(error), error, _stacktrace)

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/packages/six.py", line 770, in reraise

    raise value

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/connectionpool.py", line 699, in urlopen

    httplib_response = self._make_request(

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/connectionpool.py", line 394, in _make_request

    conn.request(method, url, **httplib_request_kw)

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/connection.py", line 239, in request

    super(HTTPConnection, self).request(method, url, body=body, headers=headers)

  File "/usr/local/lib/python3.10/http/client.py", line 1282, in request

    self._send_request(method, url, body, headers, encode_chunked)

  File "/usr/local/lib/python3.10/http/client.py", line 1328, in _send_request

    self.endheaders(body, encode_chunked=encode_chunked)

  File "/usr/local/lib/python3.10/http/client.py", line 1277, in endheaders

    self._send_output(message_body, encode_chunked=encode_chunked)

  File "/usr/local/lib/python3.10/http/client.py", line 1037, in _send_output

    self.send(msg)

  File "/usr/local/lib/python3.10/http/client.py", line 975, in send

    self.connect()

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/connection.py", line 205, in connect

    conn = self._new_conn()

  File "/home/flasktest/venv/lib/python3.10/site-packages/urllib3/connection.py", line 186, in _new_conn

    raise NewConnectionError(

urllib3.exceptions.NewConnectionError: <urllib3.connection.HTTPConnection object at 0x7f73470be7d0>: Failed to establish a new connection: [Errno 111] Connection refused

And this is the MySQL container (mysql_test) log:

2021-12-20T18:13:14.094155Z 0 [System] [MY-013602] [Server] Channel mysql_main configured to support TLS. Encrypted connections are now supported for this channel.

2021-12-20T18:13:14.098891Z 0 [Warning] [MY-011810] [Server] Insecure configuration for --pid-file: Location '/var/run/mysqld' in the path is accessible to all OS users. Consider choosing a different directory.

2021-12-20T18:13:14.110089Z 0 [System] [MY-011323] [Server] X Plugin ready for connections. Bind-address: '::' port: 33060, socket: /var/run/mysqld/mysqlx.sock

2021-12-20T18:13:14.110149Z 0 [System] [MY-010931] [Server] /usr/sbin/mysqld: ready for connections. Version: '8.0.27'  socket: '/var/run/mysqld/mysqld.sock'  port: 3306  MySQL Community Server - GPL.

mbind: Operation not permitted

mbind: Operation not permitted

2021-12-20 18:13:10+00:00 [Note] [Entrypoint]: Creating database test_db

2021-12-20 18:13:10+00:00 [Note] [Entrypoint]: Creating user test_user

2021-12-20 18:13:10+00:00 [Note] [Entrypoint]: Giving user test_user access to schema test_db


2021-12-20 18:13:10+00:00 [Note] [Entrypoint]: Stopping temporary server

2021-12-20 18:13:13+00:00 [Note] [Entrypoint]: Temporary server stopped


2021-12-20 18:13:13+00:00 [Note] [Entrypoint]: MySQL init process done. Ready for start up.

Here is the starting point of Python application (microblog.py):

from app_pkg import create_app, cli

app = create_app()
cli.register(app)

Here is the model class:

class User(UserMixin, SearchableMixin, db.Model):
    __searchable__ = ['username']
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), index=True, unique=True)
    email = db.Column(db.String(120), index=True, unique=True)
    password_hash = db.Column(db.String(128))
    posts = db.relationship('Post', backref='author', lazy='dynamic')
    about_me = db.Column(db.String(140))
    last_seen = db.Column(db.DateTime, default=datetime.utcnow)
    followed = db.relationship(
        'User', secondary=followers,
        primaryjoin=(followers.c.follower_id == id),
        secondaryjoin=(followers.c.followed_id == id),
        backref=db.backref('followers', lazy='dynamic'), lazy='dynamic')

This is my compose.yaml:

version: '3'

services:

  python_app:
    container_name: flask_test
    build: .
    env_file: .env
    ports:
      - 8000:5000
    links:
      - mysqldb:dbserver
    depends_on:
      mysqldb:
        condition: service_healthy

  mysqldb:
    container_name: mysql_test
    image: mysql:latest
    env_file: database.conf
    volumes:
      - db-data:/var/lib/mysql
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "--silent"]
      interval: 3s
      retries: 5
      start_period: 30s

volumes:
  db-data:

This is my Dockerfile:

FROM python:slim

RUN useradd flasktest

WORKDIR /home/flasktest

COPY requirements.txt requirements.txt
RUN python -m venv venv
RUN venv/bin/pip install -r requirements.txt
RUN venv/bin/pip install gunicorn pymysql cryptography

COPY app_pkg app_pkg
COPY migrations migrations
COPY microblog.py config.py boot.sh ./
RUN chmod +x boot.sh

ENV FLASK_APP microblog.py

RUN chown -R flasktest:flasktest ./
USER flasktest

EXPOSE 5000
ENTRYPOINT ["./boot.sh"]

And finally, this is the boot.sh:

#!/bin/bash

source venv/bin/activate
while true; do
    flask db upgrade
    if [[ "$?" == "0" ]]; then
        break
    fi
    echo Upgrade command failed, retrying in 5 secs...
    sleep 5
done
exec gunicorn -b :5000 --access-logfile - --error-logfile - microblog:app

And these are some necessary environment variables that are being used in the application:

DATABASE_URL=mysql+pymysql://test_user:abc123@dbserver/test_db
MYSQL_ROOT_PASSWORD=root123
MYSQL_DATABASE=test_db
MYSQL_USER=test_user
MYSQL_PASSWORD=abc123

Sorry if the question has become too lengthy. I wanted to give as much detail as possible in the question. Let me know if any other details is required. I have been trying to debug this issue for the past week, but am unable to find a way to connect the app with the sql server.

Also let me know if I should try any specific method to try to debug this issue.

Answer 1

You are currently using the docker-compose dns feature in which you can use the container name as domain name for services running in docker-compose, thats neat - unless when you rename containers;) Did you rename the mysqldb from dbserver?

If you want to continue using this feature, modify the env vars as so: (change dbserver to mysqldb)

DATABASE_URL=mysql+pymysql://test_user:abc123@mysqldb/test_db
...

If you instead what to use a more explicit approach:

In your docker-compose, you need to bind the port 3306 to your host network by

version: '3'

services:

  python_app:
    container_name: flask_test
    build: .
    env_file: .env
    ports:
      - 8000:5000
    links:
      - mysqldb:dbserver
    depends_on:
      mysqldb:
        condition: service_healthy

  mysqldb:
    container_name: mysql_test
    image: mysql:latest
    env_file: database.conf
    volumes:
      - db-data:/var/lib/mysql
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "--silent"]
      interval: 3s
      retries: 5
      start_period: 30s
    ports:
      - 3306:3306
...

Then change the env var to:

DATABASE_URL=mysql+pymysql://test_user:abc123@0.0.0.0/test_db

Thanks for all the info, you did not post too much - needed it all:)