Disable auto_minor_version_upgrade

[flaupretre]

My configuration didn't specify 'db_engine_version' and database was created with default value (11.5), which was fine. As 'auto_minor_version_upgrade' is set to 'true' in terraform-aws-modules/rds/aws, the AWS auto-upgrade mechanism then upgraded my DB to version 11.8. Now, if I run my terraform script, it fails with a message saying it cannot downgrade from 11.8 to 11.5.

The only workaround, at this time, is to modify my script and add a 'db_engine_version' parameter containing the current DB version. As soon as AWS upgrades it again, I'll have to modify my script.

My first idea was to add an 'auto_minor_version_upgrade' variable to your module but, as long as the db_engine_version parameter is mandatory and cannot be sent to the TF module as 'latest', the AWS auto-upgrade mechanism is incompatible with terraform and should be disabled.

A much smarter solution would imply a change in the TF module, which would accept the 'latest' string as db_engine_version. This would be the default and would also become the default in your module. Then, you would add an 'auto_minor_version_upgrade' variable to your module, true by default. This way, the default configuration would mean : 'delegate version mgt to AWS which will ensure DB version is always the latest one', which is the default behavior most people expect.