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.
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.
Just pull the library in using pip install django-dbconn-retry. Then add
django_dbconn_retry to INSTALLED_APPS in your settings.py.
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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