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Question

I use a Postgres 16.2 database in my Django 5.0 project configured like so:

### settings.py
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'DB_NAME',
        'USER': 'DB_USER',
        'PASSWORD': 'DB_PASS',
        'HOST': 'DB_HOST',
        'PORT': '5432',
    }
}

It works well, no issue here.

However, when I simulate a database outage (typically, I’m stopping the database service on my computer), I end up with an exception that I cannot manage to catch:

Exception in thread django-main-thread:
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/base/base.py", line 275, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.12/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/base/base.py", line 256, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/postgresql/base.py", line 277, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/psycopg2/__init__.py", line 122, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.OperationalError: could not translate host name "api-db" to address: Temporary failure in name resolution


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

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.12/threading.py", line 1010, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.12/site-packages/django/utils/autoreload.py", line 64, in wrapper
    fn(*args, **kwargs)
  File "/usr/local/lib/python3.12/site-packages/django/core/management/commands/runserver.py", line 136, in inner_run
    self.check_migrations()
  File "/usr/local/lib/python3.12/site-packages/django/core/management/base.py", line 581, in check_migrations
    executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/migrations/executor.py", line 18, in __init__
    self.loader = MigrationLoader(self.connection)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/migrations/loader.py", line 58, in __init__
    self.build_graph()
  File "/usr/local/lib/python3.12/site-packages/django/db/migrations/loader.py", line 235, in build_graph
    self.applied_migrations = recorder.applied_migrations()
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/migrations/recorder.py", line 89, in applied_migrations
    if self.has_table():
       ^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/migrations/recorder.py", line 63, in has_table
    with self.connection.cursor() as cursor:
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/base/base.py", line 316, in cursor
    return self._cursor()
           ^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/base/base.py", line 292, in _cursor
    self.ensure_connection()
  File "/usr/local/lib/python3.12/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/base/base.py", line 274, in ensure_connection
    with self.wrap_database_errors:
  File "/usr/local/lib/python3.12/site-packages/django/db/utils.py", line 91, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/base/base.py", line 275, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.12/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/base/base.py", line 256, in connect
    self.connection = self.get_new_connection(conn_params)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/utils/asyncio.py", line 26, in inner
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/db/backends/postgresql/base.py", line 277, in get_new_connection
    connection = self.Database.connect(**conn_params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/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 "api-db" to address: Temporary failure in name resolution

The exception is thrown in thread django-main-thread before entering the view.

I tried to use a middleware, but it doesn’t help:

from django.db.utils import OperationalError
from django.utils.deprecation import MiddlewareMixin
from rest_framework import status
from rest_framework.response import Response


class OperationalErrorMiddleware(MiddlewareMixin):
    def __init__(self, get_response):
        super().__init__(get_response)

    def __call__(self, request):
        try:
            return self.get_response(request)
        except OperationalError:
            return Response({'status': "DB_ERROR"}, status=status.HTTP_503_SERVICE_UNAVAILABLE)

I also tried to use Django’s handler500 and DRF (Django REST Framework) EXCEPTION_HANDLER, but these handlers do not catch the exception either.

This exception results in an empty response for the client (ERR_EMPTY_RESPONSE in Chrome) which is bad.

How can I catch this exception in order to show a more “user-friendly” error?

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Danh mục

How to catch Django’s OperationalError exception thrown in django-main-thread