expfmt: Consider filter the illegal metrics rather than drop all the metrics

[i19]

common/expfmt/decode.go

Lines 104 to 108 in 2f17f4a

	if !model.LabelValue(l.GetValue()).IsValid() {
	return fmt.Errorf("invalid label value %q", l.GetValue())
	}
	if !model.LabelName(l.GetName()).IsValid() {
	return fmt.Errorf("invalid label name %q", l.GetName())

Rather than return error cause losing the whole metrics, it would be reasonable to just filter them and log it.

[brian-brazil]

Invalid output should cause the entire scrape to fail, as partial scrapes are very difficult to deal with. I'd suggest filing a bug with the client library you're using to fix their output.

[i19]

The strange thing is, the error occur when i federate from another prometheus. i can see the illegal metric at the prometheus which was being federated. lol

[brian-brazil]

Previous versions didn't validate as much as they should have. If you upgrade your Prometheus it should handle this correctly.

[i19]

Thanks
I'm using 1.6.1
I will upgrade it as soon as possible