Counters reported as Gauges in Prometheus metrics

[danielgblanco]

What happened:
Some of the Prometheus metrics exported by the VPC CNI plugin are defined with inaccurate metric types. For example:

amazon-vpc-cni-k8s/utils/prometheusmetrics/prometheusmetrics.go

Line 64 in 27ce136

AddIPCnt = prometheus.NewGauge(

This metric (awscni_add_ip_req_count) is exported as a gauge but it has cumulative incremental values. In fact, it seems that it's used as a counter in:

amazon-vpc-cni-k8s/pkg/ipamd/rpc_handler.go

Line 70 in 27ce136

prometheusmetrics.AddIPCnt.Inc()

It seems that awscni_del_ip_req_count is correctly exported as a counter.

I probably don't have enough context on this to make a judgement call. However, I think there are probably more Gauges that are operating as Counters.

Attach logs
N/A

What you expected to happen:
I'd expect metrics to follow the semantic conventions defined in https://prometheus.io/docs/concepts/metric_types/

How to reproduce it (as minimally and precisely as possible):
Using Prometheus exporters.

Anything else we need to know?:
This may not be a critical issues if systems use Prometheus as the backend. However, it becomes a problem when Prometheus metrics are transformed into other representations. For example, OpenTelemetry Collectors will read this as a Gauge and that gives the aggregation a different meaning (e.g. one can change temporality of counters from cumulative to delta or viceversa).

Environment:

• Kubernetes version (use kubectl version): 1.28.12
• CNI Version: 1.16.3
• OS (e.g: cat /etc/os-release): Bottlerocket 1.21.0
• Kernel (e.g. uname -a): x86_64 GNU/Linux

[orsenthil]

@danielgblanco - could you verify this with the latest version of VPC CNI. This was fixed in the recent versions of CNI 1.18.3.

[orsenthil]

This is still present as Gauge in master

https://github.com/aws/amazon-vpc-cni-k8s/blob/master/utils/prometheusmetrics/prometheusmetrics.go#L64

We need to fix this to use as Counter.

[danielgblanco]

Sorry I've been on PTO, thanks for the follow up.

[hbhasker]

Looks like its not just the AddIPCnt metric that changed incorrectly to a gauge. I think this was done incorrectly in 2ac9e0a#diff-6c65a620b5206565cbd61b3390a33e02146dac52f62735909564c6b963127968L182