graphite provider treats empty result as an error

[tomasz-torcz-airspace-intelligence]

Checklist:

• I've included steps to reproduce the bug.
• I've included the version of argo rollouts.

Describe the bug

We are using Graphite as a metric provider, and in AnalysisTemplate we check for number of errors in last few minutes. When there are no errors from the component, graphite returns empty set. This is treated by provider as an error:

argo-rollouts/metricproviders/graphite/graphite.go

Lines 69 to 71 in 02d7e4f

	if len(result) == 0 {
	return metricutil.MarkMeasurementError(newMeasurement, errors.New("no values found"))
	}

Empty set of errors is an indicator of lack of errors, so it should be ok.
Moreover, this is expected for other providers -- documentation mentions how to deal with empty sets and recommends including len(results) > 0 || … in successCondition. This workaround does not work with Graphite provider, due to hardcoded fail on empty results set.

To Reproduce

Have and Graphite-using AnalyzeTemplate with settings like:

      successCondition: "len(result) > 0 ? result[0] < 1 : true"
      provider:
        graphite:
          address: http://{{ $.Values.metrics.graphiteHost }}:8080
          query: |
            target=sum(
              summarize(stats_counts.service_name.error_class.*,"2minutes","sum")
            )

Expected behavior

Empty result set should be surfaced to AnalysisRun and interpreted there.

Screenshots

Version

Rollouts v1.6.6

Logs

# Paste the logs from the rollout controller

# Logs for the entire controller:
kubectl logs -n argo-rollouts deployment/argo-rollouts

# Logs for a specific rollout:
kubectl logs -n argo-rollouts deployment/argo-rollouts | grep rollout=<ROLLOUTNAME

Message: Metric "error-rate-ra-model" assessed Error due to consecutiveErrors (5) > consecutiveErrorLimit (4): "Error Message: no values found"

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