Patch Django to retry a database connection first before failing.

## Django Database Connection Autoreconnect

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

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.

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