Metric 'gateway_service_count' type should be gauge not counter

[xueli-daisy]

From Prometheus metric type: https://prometheus.io/docs/concepts/metric_types/, I know that a counter is a cumulative metric that represents a single monotonically increasing counter whose value can only increase or be reset to zero on restart. A gauge is a metric that represents a single numerical value that can arbitrarily go up and down.

Behavior:
I can saw the value of 'gateway_service_count{function_name="***"}' goes up and down, so I think the type of gateway_service_count is gauge.
And in the code, it is also be defined as a gauge.
expectedServiceReplicasGaugeDesc := Desc{fqName: "gateway_service_count", help: "Service replicas", constLabels: {}, variableLabels: [function_name]}

Suggestion:
Change the metric 'gateway_service_count' type to a gauge in https://docs.openfaas.com/architecture/metrics/.

Thanks.

[alexellis]

This seems like a fair description of events. Thanks for letting us know that we have a metric called a count which is actually used like a gauge.

Out of interest are you wanting to send a PR for this?

Is there a chance that it could break compatibility?

Alex