component-base: initialize logging as soon as possible

In various places log messages where emitted as part of validation or even
before it (for example, cli.PrintFlags). Those log messages did not use the
final logging configuration, for example text output instead of JSON or not the
final verbosity. The last point became more obvious after moving the setup of
verbosity into logs.Options.Apply because PrintFlags never printed anything
anymore.

In order to force applications to deal with logging as soon as possible, the
Options.Validate and Options.Apply methods are now private. Applications should
use the new Options.ValidateAndApply directly after parsing.

cmd/kube-scheduler/app/options/options.go

@@ -231,7 +231,6 @@ func (o *Options) ApplyTo(c *schedulerappconfig.Config) error {
 		}
 	}
 	o.Metrics.Apply()
-	o.Logs.Apply()
 	return nil
 }
 
@@ -247,7 +246,6 @@ func (o *Options) Validate() []error {
 	errs = append(errs, o.Authorization.Validate()...)
 	errs = append(errs, o.Deprecated.Validate()...)
 	errs = append(errs, o.Metrics.Validate()...)
-	errs = append(errs, o.Logs.Validate()...)
 
 	return errs
 }

cmd/kube-scheduler/app/server.go

@@ -108,6 +108,13 @@ for more information about scheduling and the kube-scheduler component.`,
 // runCommand runs the scheduler.
 func runCommand(cmd *cobra.Command, opts *options.Options, registryOptions ...Option) error {
 	verflag.PrintAndExitIfRequested()
+
+	// Activate logging as soon as possible, after that
+	// show flags with the final logging configuration.
+	if err := opts.Logs.ValidateAndApply(); err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	}
 	cliflag.PrintFlags(cmd.Flags())
 
 	ctx, cancel := context.WithCancel(context.Background())