Backport of docs: clarify the behavior of prepending hostname to metrics into release/1.15.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #17521 to be assessed for backporting due to the inclusion of the label backport/1.15.

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The person who merged in the original PR is:
@huikang
This person should manually cherry-pick the original PR into a new backport PR,
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merge conflict error: unable to process merge commit: "0f4c45088c68c448905dca4e8463bf23f3c4f39b", automatic backport requires rebase workflow

The below text is copied from the body of the original PR.

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Description

The prepended name to the gauge metrics causes some confusion on how to query the metrics. According to the go-metrics' godoc, EnableHostname is only applicable to gauge metrics:

“EnableHostname   	bool // Enable prefixing gauge values with hostname”

Consul initializes the metrics.config with the agent configuration value “telemetry.disable_hostname”.

consul/lib/telemetry.go

Lines 327 to 329 in 720dda7

	func configureSinks(cfg TelemetryConfig, memSink metrics.MetricSink) (metrics.FanoutSink, error) {
	metricsConf := metrics.DefaultConfig(cfg.MetricsPrefix)
	metricsConf.EnableHostname = !cfg.DisableHostname

Therefore, if disable_hostname is false, hostname will be added to gauge metric names (the default behavior); otherwise, no hostname will be prepended to the metrics name of gauge type. That said, disable_hostname has no impact on other types of metrics.

This PR clarifies this behavior in consul's doc.

Links

fix #17320

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• 81fe71d - 8d6b707 - 0f4c450 - 92984da

[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR