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https://github.com/jdelic/django-dbconn-retry

Patches Django to reconnect on a failed database connection once before failing. Helping with running Django ORM through HAProxy, for example.
https://github.com/jdelic/django-dbconn-retry

django django-orm haproxy mysql pgbouncer postgresql python3

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Patches Django to reconnect on a failed database connection once before failing. Helping with running Django ORM through HAProxy, for example.

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README 

        
Django Database Connection Autoreconnect

========================================



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    :target: https://coveralls.io/github/jdelic/django-dbconn-retry?branch=master



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    :target: https://github.com/jdelic/django-dbconn-retry/actions



This library monkeypatches ``django.db.backends.base.BaseDatabaseWrapper`` so

that when a database operation fails because the underlying TCP connection was

already closed, it first tried to reconnect, instead of immediately raising

an ``OperationException``.



Why is this useful?

-------------------

I use `HAProxy`_ as a load-balancer in front of my PostgreSQL databases all

the time, sometimes in addition to ``pgbouncer``. Even though you can mostly

prevent surprises by enabling TCP keep-alive packets through `tcpka`_,

`clitcpka`_ and `srvtcpka`_, I still encounter situations where the

underlying TCP connection has been closed through the load-balancer. Most often

this results in



.. code-block::



    django.db.utils.OperationalError: server closed the connection unexpectedly

    This probably means the server terminated abnormally before or while

    processing the request.



This library patches Django such that it try to reconnect once before failing.



Another application of this is when using `Hashicorp Vault`_, where

credentials for a database connection can expire at any time and then need to

be refreshed from Vault.



How to install?

---------------

Just pull the library in using ``pip install django-dbconn-retry``. Then add

``django_dbconn_retry`` to ``INSTALLED_APPS`` in your ``settings.py``.



Signals

-------

The library provides an interface for other code to plug into the process to,

for example, allow `12factor-vault`_ to refresh the database credentials

before the code tries to reestablish the database connection. These are

implemented using `Django Signals`_.



===========================  ==================================================

Signal                       Description

===========================  ==================================================

``pre_reconnect``            Installs a hook of the type

                             ``Callable[[type, BaseDatabaseWrapper], None]``

                             that will be called before the library tries to

                             reestablish a connection. 12factor-vault uses this

                             to refresh the database credentials from Vault.

``post_reconnect``           Installs a hook of the type

                             ``Callable[[type, BaseDatabaseWrapper], None]``

                             that will be called after the library tried to

                             reestablish the connection. Success or failure has

                             not been tested at this point. So the connection

                             may be in any state.

===========================  ==================================================



Both signals send a parameter ``dbwrapper`` which points to the current instance

of ``django.db.backends.base.BaseDatabaseWrapper`` which allows the signal

receiver to act on the database connection.



License

=======



Copyright (c) 2018, Jonas Maurus

All rights reserved.



Redistribution and use in source and binary forms, with or without

modification, are permitted provided that the following conditions are met:



1. Redistributions of source code must retain the above copyright notice, this

   list of conditions and the following disclaimer.



2. Redistributions in binary form must reproduce the above copyright notice,

   this list of conditions and the following disclaimer in the documentation

   and/or other materials provided with the distribution.



3. Neither the name of the copyright holder nor the names of its contributors

   may be used to endorse or promote products derived from this software

   without specific prior written permission.



THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND

ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE

FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER

CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,

OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.



.. _12factor-vault: https://github.com/jdelic/12factor-vault/

.. _Django Signals: https://docs.djangoproject.com/en/dev/topics/signals/

.. _HAProxy: http://www.haproxy.org/

.. _tcpka:

   https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#option%20tcpka

.. _clitcpka:

   https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#4-option%20clitcpka

.. _srvtcpka:

   https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#option%20srvtcpka

.. _Hashicorp Vault: https://vaultproject.io/