Re: Could not resolve host name error in psycopg2

On 4/16/20 5:38 PM, derwin theduck wrote:
> We have been getting this error intermittently (about once a week) in
> Django with channels since switching from a local database server to a
> hosted one:
>
> could not translate host name "timescaledb" to address: Name or service
> not known
>
> Connecting directly to the server with psycopg2 in the python
> interpreter works ok:
>
> >>> import psycopg2 as pg
> >>> pg.__version__
> '2.7.7 (dt dec pq3 ext lo64)'
> >>> conn = pg.connect(host='timescaledb', database=*, user=*,
> password=*)        >>> conn.server_version
> 110005

Well I'm go out on a limb and say there is some sort of DNS resolution
issue going on.

>
> The resident database / network expert maintains that everything is ok
> on the networking side, and that django, once it establishes a
> connection, should not be attempting to reconnect.

Huh? Leaving open connections is not considered a good thing. In other
words a connection should last for as long as it takes to get it's task
done and then it should close.

>
> The problem happens not on startup, but in the middle of the day after
> processing transactions without any issues for several hours.
>
> Any idea how to go about troubleshooting / fixing this? :'(
>
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/models/query.py",
> line 276, in __iter__)
>  (    self._fetch_all())
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/models/query.py",
> line 1261, in _fetch_all)
>  (    self._result_cache = list(self._iterable_class(self)))
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/models/query.py",
> line 57, in __iter__)
>  (    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch,
> chunk_size=self.chunk_size))
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/models/sql/compiler.py",
> line 1135, in execute_sql)
>  (    cursor = self.connection.cursor())
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/utils/asyncio.py", line
> 24, in inner)
>  (    return func(*args, **kwargs))
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/backends/base/base.py",
> line 260, in cursor)
>  (    return self._cursor())
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/backends/base/base.py",
> line 236, in _cursor)
>  (    self.ensure_connection())
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/utils/asyncio.py", line
> 24, in inner)
>  (    return func(*args, **kwargs))
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/backends/base/base.py",
> line 220, in ensure_connection)
>  (    self.connect())
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/utils.py",
> line 90, in __exit__)
>  (    raise dj_exc_value.with_traceback(traceback) from exc_value)
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/backends/base/base.py",
> line 220, in ensure_connection)
>  (    self.connect())
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/utils/asyncio.py", line
> 24, in inner)
>  (    return func(*args, **kwargs))
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/backends/base/base.py",
> line 197, in connect)
>  (    self.connection = self.get_new_connection(conn_params))
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/utils/asyncio.py", line
> 24, in inner)
>  (    return func(*args, **kwargs))
>  (  File
> "/home/dduck/.local/lib/python3.7/site-packages/django/db/backends/postgresql/base.py",
> line 185, in get_new_connection)
>  (    connection = Database.connect(**conn_params))
>  (  File
> "/usr/local/lib64/python3.7/site-packages/psycopg2/__init__.py", line
> 130, in connect)
>  (    conn = _connect(dsn, connection_factory=connection_factory,
> **kwasync))
>  (  could not translate host name "timescaledb" to address: Name or
> service not known)
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com