`TypeError: cannot unpack non-iterable NoneType object` when using docker bridge network

[thentgesMindee]

---

• asyncpg version: 0.27.0
• PostgreSQL version: 12
• Python version: 3.8
• Platform: Ubuntu 22
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes

---

It seems that asyncpg is not working correctly when using an host defined using a bridge network in docker. I am actually not sure the error comes from asyncpg or docker, any idea here could be really helpful. Opening any new connection using an asyncpg connection string will result in the following error TypeError: cannot unpack non-iterable NoneType object, but only when using a network alias from a docker bridge network.

More Details + how to reproduce

I have a docker-compose.yml file looking like: (simplified for the sake of this issue)

version: '3.4'

services:
  postgresdb:
    image: postgres:12
    networks:
      proxy_network:
        aliases:
          - postgresdb_host
    env_file:
      - db.env
    ports:
      - 3333:5432
    volumes:
      - ./db/postgres:/docker-entrypoint-initdb.d
      - ./storage/postgres:/var/lib/postgresql/data

  app_one_api:
    build:
      context: ${APP_ONE_DIR}
      target: base
    ports:
      - 5000:5000
    networks:
      proxy_network:
        aliases:
          - app_one_host
    restart: on-failure
    command: bash -c "flask run --port 5000 --host 0.0.0.0"
    volumes:
      - ${APP_ONE_DIR}:/app
      - ./storage/app_one/:/storage/
    depends_on:
      - postgresdb

  app_two_api:
    build:
      context: ${APP_TWO_DIR}
      target: prod
    ports:
      - 1234:8383
    networks:
      proxy_network:
        aliases:
          - app_two_host
    restart: on-failure
    entrypoint: bash -c "python main.py"
    volumes:
      - ${APP_TWO_DIR}:/app
      - ./storage/app_two/:/storage/
    depends_on:
      - postgresdb

networks:
  proxy_network:
    driver: bridge

Where app_one is a Flask application using SQLAlchemy and psycopg2 (synchronous session, no asyncpg there), and app_two is a fastAPI application using SQLAlchemy and asyncpg.

• When I use postgresql://postgres:postgres@postgresdb_host:5432/my_db_name as an URI for the Flask application, everything is working well, meaning my proxy_network is configured correctly between app_one and postgresdb (and db is properly running)
• When I run my app_two outside of docker, but still run postgresdb container, I can properly use postgresql+asyncpg://postgres:postgres@127.0.0.1:3333/my_db_name and it works. (external host / ports), meaning the database container is working correctly
• When I do a HTTP call from my app_two container, to an endpoint of app_one, using http://app_one_host:5000 as URI, it works correctly, meaning app_two and app_one are also properly linked to the bridge network.

However, using postgresql+asyncpg://postgres:postgres@postgresdb_host:5432/my_db_name as my database URI from within the docker container of app_two, here is the error I get when trying to open any new connection:

   File "/usr/local/lib/python3.8/site-packages/asyncpg/connect_utils.py", line 825, in __connect_addr
     tr, pr = await compat.wait_for(connector, timeout=timeout)
 TypeError: cannot unpack non-iterable NoneType object

see full error stacktrace:

``` File "/app/app/db/session.py", line 85, in check_dbs async with self.engines[bind].begin() as connection: File "/usr/local/lib/python3.8/site-packages/sqlalchemy/ext/asyncio/base.py", line 66, in __aenter__ return await self.start(is_ctxmanager=True) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/ext/asyncio/engine.py", line 599, in start await self.conn.start(is_ctxmanager=is_ctxmanager) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/ext/asyncio/engine.py", line 157, in start await (greenlet_spawn(self.sync_engine.connect)) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 126, in greenlet_spawn result = context.throw(*sys.exc_info()) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/future/engine.py", line 406, in connect return super(Engine, self).connect() File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 3320, in connect return self._connection_cls(self, close_with_result=close_with_result) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 96, in __init__ else engine.raw_connection() File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 3399, in raw_connection return self._wrap_pool_connect(self.pool.connect, _connection) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 3366, in _wrap_pool_connect return fn() File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/base.py", line 327, in connect return _ConnectionFairy._checkout(self) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/base.py", line 894, in _checkout fairy = _ConnectionRecord.checkout(pool) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/base.py", line 493, in checkout rec = pool._do_get() File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/impl.py", line 146, in _do_get self._dec_overflow() File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py", line 70, in __exit__ compat.raise_( File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/compat.py", line 211, in raise_ raise exception File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/impl.py", line 143, in _do_get return self._create_connection() File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/base.py", line 273, in _create_connection return _ConnectionRecord(self) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/base.py", line 388, in __init__ self.__connect() File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/base.py", line 691, in __connect pool.logger.debug("Error on connect(): %s", e) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py", line 70, in __exit__ compat.raise_( File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/compat.py", line 211, in raise_ raise exception File "/usr/local/lib/python3.8/site-packages/sqlalchemy/pool/base.py", line 686, in __connect self.dbapi_connection = connection = pool._invoke_creator(self) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/create.py", line 574, in connect return dialect.connect(*cargs, **cparams) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/default.py", line 598, in connect return self.dbapi.connect(*cargs, **cparams) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/dialects/postgresql/asyncpg.py", line 780, in connect await_only(self.asyncpg.connect(*arg, **kw)), File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 68, in await_only return current.driver.switch(awaitable) File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 121, in greenlet_spawn value = await result File "/usr/local/lib/python3.8/site-packages/asyncpg/connection.py", line 2092, in connect return await connect_utils._connect( File "/usr/local/lib/python3.8/site-packages/asyncpg/connect_utils.py", line 881, in _connect return await _connect_addr( File "/usr/local/lib/python3.8/site-packages/asyncpg/connect_utils.py", line 773, in _connect_addr return await __connect_addr(params, timeout, True, *args) File "/usr/local/lib/python3.8/site-packages/asyncpg/connect_utils.py", line 825, in __connect_addr tr, pr = await compat.wait_for(connector, timeout=timeout) TypeError: cannot unpack non-iterable NoneType object ```

With all those experiments I did, I cannot find what is the issue, except that it happens only when using asyncpg + bridge network. Bridge network with psycopg2 works fine, as well as asyncpg without bridge network hosts. Combining both fails.

I tried to add as much info as possible on my issue and how to reproduce, but feel free to ask anything I may have forgotten!

[elprans]

I could not reproduce this on my end using just asyncpg (without SQLAlchemy). Here's the compose file I used:

services:
  postgresdb:
    image: postgres:12
    networks:
      proxy_network:
        aliases:
          - postgresdb_host
    env_file:
      - db.env
    ports:
      - 3333:5432

  app:
    build:
      context: .
    ports:
      - 1234:8383
    networks:
      proxy_network:
        aliases:
          - app_two_host
    restart: on-failure
    entrypoint: bash -c "python /usr/local/bin/test_bug1030.py"
    depends_on:
      - postgresdb

networks:
  proxy_network:
    driver: bridge

test_bug1030.py:

import asyncio
import asyncpg

async def main():
    con = await asyncpg.connect('postgresql://postgres:foo@postgresdb_host:5432/postgres')
    print(await con.fetchval('select 1'))
    await con.close()

asyncio.run(main())