master-config.yaml with invalid keys are not validated

[gnufied]

Sometimes our users put keys in YAML in subtly incorrect indentation. This does not cause any validation errors or anything like that and master controllers start just fine but intended purpose of putting the key in YAML does not work.

YAML being whitespace senstive makes it harder to notice. Can we just start validating the keys in YAML and print warning or errors or even refuse to start the process if something is wrong with YAML?

Examples:

1. https://bugzilla.redhat.com/show_bug.cgi?id=1582231
2. https://bugzilla.redhat.com/show_bug.cgi?id=1570085

[gnufied]

cc @liggitt @smarterclayton

[liggitt]

Can we just start validating the keys in YAML

there's no facility for negative schema validation in our current json/yaml machinery. the data decodes to go structs, and unknown fields get dropped in the process, with no programmatic indication that occurred (this is identical to the way our API objects work when decoded by the server)

and print warning or errors or even refuse to start the process if something is wrong with YAML?

an unexpected key is indistinguishable from a config field added in a future version of the server. we should think carefully about hard-failing on that

[enj]

Just waiting on Go 1.10 for #19106

It warns on unexpected fields but does not fail.

[gnufied]

It warns on unexpected fields but does not fail.

Awesome, yeah I think warning should be "good enough" compromise for now.