Fix incorrect container name gathered in docker input (#4391)

plugins/inputs/docker/docker.go

@@ -365,10 +365,18 @@ func (d *Docker) gatherContainer(
 ) error {
 	var v *types.StatsJSON
 	// Parse container name
-	cname := "unknown"
-	if len(container.Names) > 0 {
-		// Not sure what to do with other names, just take the first.
-		cname = strings.TrimPrefix(container.Names[0], "/")
+	var cname string
+	for _, name := range container.Names {
+		trimmedName := strings.TrimPrefix(name, "/")
+		match := d.containerFilter.Match(trimmedName)
+		if match {
+			cname = trimmedName
+			break
+		}
+	}
+
+	if cname == "" {
+		return nil
 	}
 
 	// the image name sometimes has a version part, or a private repo
@@ -391,10 +399,6 @@ func (d *Docker) gatherContainer(
 		"container_version": imageVersion,
 	}
 
-	if !d.containerFilter.Match(cname) {
-		return nil
-	}
-
 	ctx, cancel := context.WithTimeout(context.Background(), d.Timeout.Duration)
 	defer cancel()
 	r, err := d.client.ContainerStats(ctx, container.ID, false)
@@ -411,6 +415,9 @@ func (d *Docker) gatherContainer(
 	}
 	daemonOSType := r.OSType
 
+	// use common (printed at `docker ps`) name for container
+	tags["container_name"] = strings.TrimPrefix(v.Name, "/")
+
 	// Add labels to tags
 	for k, label := range container.Labels {
 		if d.labelFilter.Match(k) {
@@ -461,12 +468,12 @@ func (d *Docker) gatherContainer(
 		acc.AddFields("docker_container_health", healthfields, tags, time.Now())
 	}
 
-	gatherContainerStats(v, acc, tags, container.ID, d.PerDevice, d.Total, daemonOSType)
+	parseContainerStats(v, acc, tags, container.ID, d.PerDevice, d.Total, daemonOSType)
 
 	return nil
 }
 
-func gatherContainerStats(
+func parseContainerStats(
 	stat *types.StatsJSON,
 	acc telegraf.Accumulator,
 	tags map[string]string,