Type loss and metric rename in prometheus input → prometheus output

[zagy]

Bug report

Loading the data with telegraf Prometheus input and exporting it with the prometheus output (e.g. haproxy-exporter --[prometheus protocol]--telegraf---[prometheus protocol]---…) yields

• Metric is being renamed to *_<type> (e.g. haproxy_up becomes haproxy_up_gauge)
• Type becomes untyped

Relevant telegraf.conf:

[inputs.prometheus]
urls = ["http://localhost:9127/metrics"]

[outputs.prometheus_client]
listen = "172.22.49.216:9126"

System info:

Tested in

• 1.2.1
• 1.3.0

Steps to reproduce:

1. Setup https://github.com/prometheus/haproxy_exporter
2. Point telegraf to haproxy_export (prometheus input)
3. Setup telegraf output prometheus_client
4. See that metrics are renamed after they come out of telegraf.

Expected behavior:

• No rename of metric
• Keep type

Actual behavior:

• Metric is being renamed to *_<type> (e.g. haproxy_up becomes haproxy_up_gauge)
• Type becomes untyped

haproxy exporter gives:

# HELP haproxy_up Was the last scrape of haproxy successful.
# TYPE haproxy_up gauge
haproxy_up 1

Telegraf exports:

# HELP haproxy_up_gauge Telegraf collected metric
# TYPE haproxy_up_gauge untyped
haproxy_up_gauge{host="hostname", url="http://localhost:9127/metrics"} 1

[spowser]

Can confirm this issue. Any metrics that traverse through telegraf are losing their metric types. We also have Prometheus as the input and output.

[dylanzr]

I can confirm this is present in 1.4.1. I think the offending line is found here

			// the prometheus input.
			var mname string
			if fn == "value" {
				mname = sanitize(point.Name())
			} else {
				mname = sanitize(fmt.Sprintf("%s_%s", point.Name(), fn))
                        }

[dylanzr]

After thinking about this a little further, I think this would have to be addressed on the input and not the output. Trying to address this on the output would be difficult, as histogram types would have to construct new histogram labels and use the field names as the label value.

For any other single value metric, the field name should get used as the type.

[spowser]

Will this be added to the 1.5 milestone?

[jdoupe]

This is mostly addressed by #3337. Types are still lost, but metric names are no longer mangled unnecessarily.