[receiver/dockerstat] Only one label/envVar is added even if multiple ones are specified

[paologallinaharbur]

Component(s)

receiver/dockerstats

What happened?

When running the dockerstat receiver I noticed that setting container_labels_to_metric_labels with 2 or more labels results in just either one of the labels included as a resource attribute.

receivers:
  docker_stats:
    container_labels_to_metric_labels:
      "com.docker.compose.config-hash": "com.docker.compose.config-hash"
      "com.docker.compose.container-number": "new.name"

Steps to Reproduce

Run the exporters with 2 or more entries of container_labels_to_metric_labels

Expected Result

Both labels included

Actual Result

Only one of the two was present at a time.

Root cause

Basically here we have a loop and we are using directly the labels variable without saving a local copy when creating resourceMetricsOptions.
Therefore when running the loop multiple resourceMetricsOptions are appended, but all shares the same value for label, i.e. the latest one applied.

The following code solves the issue:

	for k, label := range r.config.ContainerLabelsToMetricLabels {

		l := label  <- Adding this shadows the loop variable and fixes the code

		if v := container.Config.Labels[k]; v != "" {
			resourceMetricsOptions = append(resourceMetricsOptions, func(ras metadata.ResourceAttributesSettings, rm pmetric.ResourceMetrics) {
				rm.Resource().Attributes().PutStr(l, v)
			})
		}
	}

I checked into the code and envVars are affected as well when setting env_vars_to_metric_labels.

Notice that there are currently discussions regarding modifying the configuration experience and the implementation to include labels. See #13848

Collector version

691044b

[github-actions]

Pinging code owners:

• receiver/dockerstat: @rmfitzpatrick @jamesmoessis
• receiver/dockerstats: @rmfitzpatrick @jamesmoessis

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[paologallinaharbur]

Ideally, we would need a fix and a test covering such use-case. I can take ownership of fixing it if you want.