Django Dbconn Retry Save
Patches Django to reconnect on a failed database connection once before failing. Helping with running Django ORM through HAProxy, for example.
Django Database Connection Autoreconnect
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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:
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Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
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.
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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/
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