[openstack-dev] [oslo.config] Config files overriding CLI: The path of most surprise.

John Dennis jdennis at redhat.com
Tue Jul 2 14:03:47 UTC 2013

On 07/01/2013 05:52 PM, Clint Byrum wrote:
> Last week I went to use oslo.config in a utility I am writing called
> os-collect-config[1]...
> While running unit tests on the main() method that is used for the CLI,
> I was surprised to find that my unit tests were picking up values from
> a config file I had created just as a test. The tests can be fixed to
> disable config file lookups, but what was more troublesome was that the
> config file was overriding values I was passing in as sys.argv.
> I have read the thread[2] which suggest that CLI should defer to config
> file because config files are somehow less permanent than the CLI.
> I am writing today to challenge that notion, and also to suggest that even
> if that is the case, it is inappropriate to have oslo.config operate in
> such a profoundly different manner than basically any other config library
> or system software in general use. CLI options are _for config files_
> and if packagers are shipping configurations in systemd unit files,
> upstart jobs, or sysvinits, they are doing so to control the concerns
> of that particular invocation of whatever command they are running,
> and not to configure the software entirely.
> CLI args are by definition ephemeral, even if somebody might make them
> "permanent" in their system, I doubt any packager would then expect that
> these CLI args would be overridden by any config files. This default is
> just wrong, and needs to be fixed.


When I read "Option values in config files override those on the command
line." in the cfg.py docstring I thought surely that must be a typo
because it's it's the opposite of years of established practice.

I think the following captures the expected behavior

> I was also confused by the ordering in this list, though when I read more carefully it seems to agree with me:
>> - Default value in source code
>> - Overridden by value in config file
>> - Overridden by value in environment variable
>> - Overridden by value given as command line option
> I'd like to rewrite that list as
> - Value given as a command line option
> - Failing that, value in environment variable
> - Failing that, value in config file
> - Failing that, default value in source code 


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