Django unable to translate host for managed postgresql Database

I have app on the app platform that consists of a React front end, a Django backend, and a managed PostgreSQL database. The frontend is deployed from source (github) and builds and deploys without issues. The backend (django) is a container built using github actions and pushed to a DigitalOcean container registy. The Dockerfile is below (2 part build, wheels copied to runtime container, no entrypoint run):

###########
# BUILDER #
###########

# pull official base image
FROM --platform=linux/amd64 python:3.11-bookworm AS visivi4_builder

# set work directory
WORKDIR /usr/src/visivi4

# set environment variables
ENV PYTHONDONTWRITEBYTECODE=1
ENV PYTHONUNBUFFERED=1

# install psycopg2 dependencies
RUN apt-get update \
    && apt-get install gcc git proj-bin libgdal-dev -y \
    && pip install --upgrade pip

# install dependencies
COPY ./requirements.txt .
COPY ./requirements/ ./requirements/
RUN pip wheel --no-cache-dir --wheel-dir /usr/src/visivi4/wheels -r requirements/production.txt


#########
# FINAL #
#########

# pull official base image
FROM --platform=linux/amd64 python:3.11-slim-bookworm AS visivi4_runtime

# create directory for the app user
RUN mkdir -p /home/visivi4

ARG USERNAME=visivi4
ARG USER_UID=1000
ARG USER_GID=$USER_UID

# create the appropriate directories
ENV HOME=/home/visivi4
ENV APP_HOME=/home/visivi4/web
# create the app user
RUN groupadd --gid $USER_GID $USERNAME \
    && useradd --uid $USER_UID --gid $USER_GID -m $USERNAME \
    && mkdir $APP_HOME \
    && mkdir $APP_HOME/staticfiles

WORKDIR $APP_HOME

# install geo libraries, note these paths need to be set in .env files
RUN apt-get update \
    && RUN_DEPS=" \
    libgdal32 \
    libgeos-c1v5 \
    " \
    # && UNUSED=" \
    # # gcc-12 \
    # # mariadb-common \
    # # mysql-common \
    # " \
    && apt-get install --no-install-recommends -y $RUN_DEPS \
    && rm -rf /var/lib/apt/lists/*
# && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false $UNUSED

COPY --from=visivi4_builder /usr/src/visivi4/wheels /wheels

RUN pip install --no-cache --no-deps /wheels/*

# copy project
COPY --chown=visivi4:visivi4 . $APP_HOME

# copy entrypoint.prod.sh
COPY --chown=visivi4:visivi4 ./entrypoint.vis4.sh .

RUN sed -i 's/\r$//g'  ./entrypoint.vis4.sh \
    && chmod +x  ./entrypoint.vis4.sh \
    && rm -f .env

RUN chown visivi4:visivi4 $APP_HOME/staticfiles

# change to the app user
USER visivi4

# run entrypoint.prod.sh
# ENTRYPOINT ["./entrypoint.vis4.sh"]

EXPOSE 8000
EXPOSE 25060

ENV DJANGO_SETTINGS_MODULE=config.settings.production

# DigitalOcean AppPlatform allows setting of a RunCommand, use that
# CMD ["gunicorn", "-w", "2", "-b", "0.0.0.0:8000", "config.wsgi:application"]

This deploys happily.

Once I attempt to connect to the backend I receive an error that it cannot resolve the host for the database.

[2024-08-14 12:27:59,702] ERROR django.request:241 -> Internal Server Error: /api/logincheck/
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 289, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 270, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/contrib/gis/db/backends/postgis/base.py", line 112, in get_new_connection
    connection = super().get_new_connection(conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/postgresql/base.py", line 275, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/psycopg2/__init__.py", line 122, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.OperationalError: could not translate host name "db-postgisql-lon1-vis4-staging-do-user-1111702-0.m.db.ondigitalocean.com" to address: Name or service not known
visivi4-backend 2024-08-14T12:28:00.164954040Z
The above exception was the direct cause of the following exception:
visivi4-backend 2024-08-14T12:28:00.164960470Z Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/contextlib.py", line 80, in inner
    with self._recreate_cm():
  File "/usr/local/lib/python3.11/site-packages/django/db/transaction.py", line 198, in __enter__
    if not connection.get_autocommit():
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 464, in get_autocommit
    self.ensure_connection()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 288, in ensure_connection
    with self.wrap_database_errors:
  File "/usr/local/lib/python3.11/site-packages/django/db/utils.py", line 91, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 289, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 270, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/contrib/gis/db/backends/postgis/base.py", line 112, in get_new_connection
    connection = super().get_new_connection(conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/postgresql/base.py", line 275, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/psycopg2/__init__.py", line 122, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
django.db.utils.OperationalError: could not translate host name "db-postgisql-lon1-vis4-staging-do-user-1111702-0.m.db.ondigitalocean.com" to address: Name or service not known
visivi4-backend 2024-08-14T12:28:00.176060723Z [2024-08-14 12:27:59,698] ERROR django.request:241 -> Internal Server Error: /api/users/user-info/
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 289, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 270, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/contrib/gis/db/backends/postgis/base.py", line 112, in get_new_connection
    connection = super().get_new_connection(conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/postgresql/base.py", line 275, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/psycopg2/__init__.py", line 122, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.OperationalError: could not translate host name "db-postgisql-lon1-vis4-staging-do-user-1111702-0.m.db.ondigitalocean.com" to address: Name or service not known
visivi4-backend 2024-08-14T12:28:00.176173954Z
The above exception was the direct cause of the following exception:
visivi4-backend 2024-08-14T12:28:00.176180871Z Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/contextlib.py", line 80, in inner
    with self._recreate_cm():
  File "/usr/local/lib/python3.11/site-packages/django/db/transaction.py", line 198, in __enter__
    if not connection.get_autocommit():
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 464, in get_autocommit
    self.ensure_connection()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 288, in ensure_connection
    with self.wrap_database_errors:
  File "/usr/local/lib/python3.11/site-packages/django/db/utils.py", line 91, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 289, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 270, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/contrib/gis/db/backends/postgis/base.py", line 112, in get_new_connection
    connection = super().get_new_connection(conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/postgresql/base.py", line 275, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/psycopg2/__init__.py", line 122, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
django.db.utils.OperationalError: could not translate host name "db-postgisql-lon1-vis4-staging-do-user-1111702-0.m.db.ondigitalocean.com" to address: Name or service not known
visivi4-backend 2024-08-14T12:28:00.672151627Z [2024-08-14 12:28:00,355] ERROR django.request:241 -> Internal Server Error: /api/accounts/login/
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 289, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 270, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/contrib/gis/db/backends/postgis/base.py", line 112, in get_new_connection
    connection = super().get_new_connection(conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/postgresql/base.py", line 275, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/psycopg2/__init__.py", line 122, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.OperationalError: could not translate host name "db-postgisql-lon1-vis4-staging-do-user-1111702-0.m.db.ondigitalocean.com" to address: Name or service not known
visivi4-backend 2024-08-14T12:28:00.672266270Z
The above exception was the direct cause of the following exception:
visivi4-backend 2024-08-14T12:28:00.672274758Z Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/contextlib.py", line 80, in inner
    with self._recreate_cm():
  File "/usr/local/lib/python3.11/site-packages/django/db/transaction.py", line 198, in __enter__
    if not connection.get_autocommit():
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 464, in get_autocommit
    self.ensure_connection()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 288, in ensure_connection
    with self.wrap_database_errors:
  File "/usr/local/lib/python3.11/site-packages/django/db/utils.py", line 91, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 289, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/base/base.py", line 270, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/contrib/gis/db/backends/postgis/base.py", line 112, in get_new_connection
    connection = super().get_new_connection(conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/django/db/backends/postgresql/base.py", line 275, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/psycopg2/__init__.py", line 122, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
django.db.utils.OperationalError: could not translate host name "db-postgisql-lon1-vis4-staging-do-user-1111702-0.m.db.ondigitalocean.com" to address: Name or service not known

For clarification, the above hostname is my managed postgres cluster

Things I’ve tried:

• set the DATABASE_URL env variable to various iterations of ${mydbname.DATABASE_URL}, this generally gives a different error of “set mydbname.DATABASE_URL”
• exposed the ports stated in the db connection string in the dockerfile
• exposed the ports in the app platform config
• set DATABASE_URL to the connection string in the database component

I have been able to use the console to confirm that DNS is working (used python REPL in the console to send a GET to www.google.com and received 200) I can connect to the database using the connection string and psql from my local machine.

I’m hoping this is something basic I am missing as the django backend will happily connect to a dev database, but that is not sufficient for my production needs.

Thank you for your time

Simon