Comment 2 for bug 1196368

In fact, since the user can only override option values by using a configuration file they MUST either

1) supply values in their user-supplied config file for ALL options listed in the original system configuration file; or,
2) use an initial --config-file directive on the command line to force the processing of the original system configuration file before any --config-file directive pointing to a user-provided configuration file.

If this isn't done, the user runs the risk of having the value of some option that they haven't even specified changing.

This can arise if the default value for the option differs in the source code from that supplied in the system configuration file. (Easy to happen as an installation is tuned). Supplying a user-provided configuration file on the command line _suppresses_ processing of the system configuration file causing the option value to revert to the default provided in the source code even though it is mentioned on neither the command line nor the user-supplied configuration file.

I agree with Monty Taylor in that I find the order/rules for oslo.config processing inconvenient and surprising.