The recommendation from #sig-cli was to print usage, then the error. Extra care
is taken to only print the usage instruction when the error really was about
flag parsing.
Taking kube-scheduler as example:
$ _output/bin/kube-scheduler
I0929 09:42:42.289039 149029 serving.go:348] Generated self-signed cert in-memory
...
W0929 09:42:42.489255 149029 client_config.go:620] error creating inClusterConfig, falling back to default config: unable to load in-cluster configuration, KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT must be defined
E0929 09:42:42.489366 149029 run.go:98] "command failed" err="invalid configuration: no configuration has been provided, try setting KUBERNETES_MASTER environment variable"
$ _output/bin/kube-scheduler --xxx
Usage:
kube-scheduler [flags]
...
--vmodule moduleSpec
comma-separated list of pattern=N settings for file-filtered logging
Error: unknown flag: --xxx
The kubectl behavior doesn't change:
$ _output/bin/kubectl get nodes
Unable to connect to the server: dial tcp: lookup xxxx: No address associated with hostname
$ _output/bin/kubectl --xxx
Error: unknown flag: --xxx
See 'kubectl --help' for usage.
All Kubernetes commands should show flags with hyphens in their help text even
when the flag originally was defined with underscore. Converting a command to
this style is not breaking its command line API because the old-style parameter
with underscore is accepted as alias.
The easiest solution to achieve this is to set normalization shortly before
running the command in the new central cli.Run or the few places where that
function isn't used yet.
There may be some texts which depends on normalization at flag definition time,
like the --logging-format usage warning. Those get generated assuming that
hyphens will be used.
It wasn't documented that InitLogs already uses the log flush frequency, so
some commands have called it before parsing (for example, kubectl in the
original code for logs.go). The flag never had an effect in such commands.
Fixing this turned into a major refactoring of how commands set up flags and
run their Cobra command:
- component-base/logs: implicitely registering flags during package init is an
anti-pattern that makes it impossible to use the package in commands which
want full control over their command line. Logging flags must be added
explicitly now, something that the new cli.Run does automatically.
- component-base/logs: AddFlags would have crashed in kubectl-convert if it
had been called because it relied on the global pflag.CommandLine. This
has been fixed and kubectl-convert now has the same --log-flush-frequency
flag as other commands.
- component-base/logs/testinit: an exception are tests where flag.CommandLine has
to be used. This new package can be imported to add flags to that
once per test program.
- Normalization of the klog command line flags was inconsistent. Some commands
unintentionally didn't normalize to the recommended format with hyphens. This
gets fixed for sample programs, but not for production programs because
it would be a breaking change.
This refactoring has the following user-visible effects:
- The validation error for `go run ./cmd/kube-apiserver --logging-format=json
--add-dir-header` now references `add-dir-header` instead of `add_dir_header`.
- `staging/src/k8s.io/cloud-provider/sample` uses flags with hyphen instead of
underscore.
- `--log-flush-frequency` is not listed anymore in the --logging-format flag's
`non-default formats don't honor these flags` usage text because it will also
work for non-default formats once it is needed.
- `cmd/kubelet`: the description of `--logging-format` uses hyphens instead of
underscores for the flags, which now matches what the command is using.
- `staging/src/k8s.io/component-base/logs/example/cmd`: added logging flags.
- `apiextensions-apiserver` no longer prints a useless stack trace for `main`
when command line parsing raises an error.
