(psycopg2.OperationalError) could not connect to server: Connection refused Is the server

Question

I am trying to connect two docker containers, one posgresql and the other a python flask application. both are linking correctly, all connection variables in the python app are taken directly from the ones in the postgres container that are exposed via linking and are identical to those found when inspecting the postgresql container. when I use psql with the exact parameters from the connection string ie:

psql -p 5432 -h 172.17.0.2 -d mydb -U user

connection to the database in the postgres container is successful, so I know that postgres is communicating correctly over the specified ports etc. however, when I attempt to connect to the database via flask with the same connection variables I get this error:

Traceback (most recent call last): File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1122, in _do_get return self._pool.get(wait, self._timeout) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/queue.py", line 145, in get raise Empty sqlalchemy.util.queue.Empty

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2138, in _wrap_pool_connect return fn() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 328, in unique_connection return _ConnectionFairy._checkout(self) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 766, in _checkout fairy = _ConnectionRecord.checkout(pool) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 516, in checkout rec = pool._do_get() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1138, in _do_get self._dec_overflow() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 60, in exit compat.reraise(exc_type, exc_value, exc_tb) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 187, in reraise raise value File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1135, in _do_get return self._create_connectio n() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 333, in _create_connection return _ConnectionRecord(self) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 461, in init self. connect(first_connect_check=True) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 651, in __connect connection = pool._invoke_creator(self) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/strategies.py", line 105, in connect return dialect.connect(*cargs, **cparams) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 393, in connect return self.dbapi.connect(*cargs, **cparams) File "/usr/local/lib/python3.6/site-packages/psycopg2/__init .py", line 164, in connect conn = _connect(dsn, connection_factory=connection_factory, async=async) psycopg2.OperationalError: could not connect to server: Connection refused Is the server running on host "172.17.0.2" and accepting TCP/IP connections on port 5432?

The above exception was the direct cause of the following exception:

Traceback (most recent call last): File "./wsgi.py", line 14, in app = getModule("/var/www", name).app File "./wsgi.py", line 5, in getModule return imp.load_source(module, ("%s/%s.py" % (path, name))) File "/usr/local/lib/python3.6/imp.py", line 172, in load_source module = _load(spec) File "/var/www/backend.py", line 3, in import json, logging, db, os File "/var/www/db.py", line 36, in engine.connect() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2082, in connect return self._connection_cls(self, **kwargs) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 90, in init if connection is not None else engine.raw_connection() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2168, in raw_connection self.pool.unique_connection, _connection) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2142, in _wrap_pool_connect e, dialect, self) File "/usr/local/lib/python3.6/site-pack ages/sqlalchemy/engine/base.py", line 1456, in _handle_dbapi_exception_noconnection exc_info File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause reraise(type(exception), exception, tb=exc_tb, cause=cause) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 186, in reraise raise value.with_traceback(tb) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2138, in _wrap_pool_connect return fn() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 328, in unique_connection return _ConnectionFairy._checkout(self) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 766, in _checkout fairy = _ConnectionRecord.checkout(pool) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 516, in checkout rec = pool._do_get() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1138, in _do_get self._dec_overflow() File "/usr/local /lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 60, in exit compat.reraise(exc_type, exc_value, exc_tb) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 187, in reraise raise value File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1135, in _do_get return self._create_connection() File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 333, in _create_connection return _ConnectionRecord(self) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 461, in init self. connect(first_connect_check=True) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 651, in __connect connection = pool._invoke_creator(self) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/strategies.py", line 105, in connect return dialect.connect(*cargs, **cparams) File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 393, in connect return self.dbapi.connect(*cargs, **cparams) File "/usr/local/lib/python3.6/site-packages/psycopg2/__init .py", line 164, in connect conn = _connect(dsn, connection_factory=connection_factory, async=async) sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) could not connect to server: Connection refused Is the server running on host "172.17.0.2" and accepting TCP/IP connections on port 5432?

below is the code in my flask app leading up to the exception:

import os, logging, json
from datetime import datetime
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
from sqlalchemy import BigInteger, Integer, String, DateTime, Column, Table, ForeignKey, create_engine
from sqlalchemy.dialects.postgresql import JSON
from sqlalchemy.orm import scoped_session, sessionmaker, relationship
from sqlalchemy.ext.declarative import declarative_base

user = os.environ.get('DB_USER','user')
password = os.environ.get('DB_PASSWORD','password')
address = os.environ.get('DB_ADDR','0.0.0.0')
port = os.environ.get('DB_PORT','')
name = os.environ.get('DB_NAME','')

db_url = "postgresql://%s:%s@%s:%s/%s" % (user, password, address, port, name) 

engine = create_engine(db_url, convert_unicode=True, client_encoding='utf8')

print (engine)

engine.connect()

when I log the "engine" I get this:

Engine(postgresql://user:***@172.17.0.2:5432/mydb)

which again matches the parameters used in succesful database connection with the database from my host computer.

I'm assuming there must be something wrong with my python code since the docker containers appear by all accounts to be working correctly.

any help would be much appreciated, thank you.

Answer 1

所以我的代码实际上没问题，发生的是一种竞争情况，其中python在数据库完全初始化并接受连接之前发送连接请求。