cli: add --selector flag to proxy-metrics and multi-resource to routes

Closes #2734

Two additions toward full kubectl-style resource selector support:

1. viz routes — multi-resource support
   Change Args from ExactArgs(1) to MinimumNArgs(1) so that multiple
   resources can be specified:

     linkerd viz routes svc/webapp svc/api -n test

   The API client is constructed once before the loop; each resource
   produces one TopRoutesRequest and the outputs are concatenated.

2. diagnostics proxy-metrics — --selector / -l flag
   Add a labelSelector field to metricsOptions and register the
   --selector/-l flag. When no positional argument is given but a
   selector is provided, GetPodsBySelector (new helper in pkg/k8s) is
   called to list matching pods directly:

     linkerd diagnostics proxy-metrics -n emojivoto -l app=web

   GetPodsBySelector wraps a plain CoreV1().Pods().List() call with
   the label-selector string, consistent with the existing getPods()
   helper in cli/cmd/identity.go.

   A positional argument is still accepted and takes precedence when
   both are given; omitting both is an error.

Signed-off-by: Sudheer Obbu <mail2sudheerobbu@gmail.com>

Author: mail2sudheerobbu-oss

cli/cmd/metrics.go

@@ -2,40 +2,45 @@ package cmd
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"time"
 
 	pkgcmd "github.com/linkerd/linkerd2/pkg/cmd"
 	"github.com/linkerd/linkerd2/pkg/k8s"
 	"github.com/spf13/cobra"
+	corev1 "k8s.io/api/core/v1"
 )
 
 type metricsOptions struct {
-	namespace string
-	pod       string
-	obfuscate bool
+	namespace     string
+	pod           string
+	obfuscate     bool
+	labelSelector string
 }
 
 func newMetricsOptions() *metricsOptions {
 	return &metricsOptions{
-		pod:       "",
-		obfuscate: false,
+		pod:           "",
+		obfuscate:     false,
+		labelSelector: "",
 	}
 }
 
 func newCmdMetrics() *cobra.Command {
 	options := newMetricsOptions()
 
 	cmd := &cobra.Command{
-		Use:   "proxy-metrics [flags] (RESOURCE)",
+		Use:   "proxy-metrics [flags] [(RESOURCE)]",
 		Short: "Fetch metrics directly from Linkerd proxies",
 		Long: `Fetch metrics directly from Linkerd proxies.
 
   This command initiates a port-forward to a given pod or set of pods, and
   queries the /metrics endpoint on the Linkerd proxies.
 
   The RESOURCE argument specifies the target resource to query metrics for:
-  (TYPE/NAME)
+  (TYPE/NAME). Alternatively, use --selector (-l) to select pods by label
+  without specifying a resource name.
 
   Examples:
   * cronjob/my-cronjob
@@ -61,14 +66,21 @@ func newCmdMetrics() *cobra.Command {
   # Get metrics from the web deployment in the emojivoto namespace.
   linkerd diagnostics proxy-metrics -n emojivoto deploy/web
 
+  # Get metrics from all pods with a given label in the emojivoto namespace.
+  linkerd diagnostics proxy-metrics -n emojivoto -l app=web
+
   # Get metrics from the linkerd-destination pod in the linkerd namespace.
   linkerd diagnostics proxy-metrics -n linkerd $(
     kubectl --namespace linkerd get pod \
       --selector linkerd.io/control-plane-component=destination \
       --output name
   )`,
-		Args: cobra.ExactArgs(1),
+		Args: cobra.MaximumNArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
+			if len(args) == 0 && options.labelSelector == "" {
+				return errors.New("must specify a resource or --selector")
+			}
+
 			if options.namespace == "" {
 				options.namespace = pkgcmd.GetDefaultNamespace(kubeconfigPath, kubeContext)
 			}
@@ -77,7 +89,13 @@ func newCmdMetrics() *cobra.Command {
 				return err
 			}
 
-			pods, err := k8s.GetPodsFor(cmd.Context(), k8sAPI, options.namespace, args[0])
+			var pods []corev1.Pod
+			if len(args) == 0 {
+				// selector-only mode: list pods matching the label selector
+				pods, err = k8s.GetPodsBySelector(cmd.Context(), k8sAPI, options.namespace, options.labelSelector)
+			} else {
+				pods, err = k8s.GetPodsFor(cmd.Context(), k8sAPI, options.namespace, args[0])
+			}
 			if err != nil {
 				return err
 			}
@@ -111,6 +129,7 @@ func newCmdMetrics() *cobra.Command {
 
 	cmd.PersistentFlags().StringVarP(&options.namespace, "namespace", "n", options.namespace, "Namespace of resource")
 	cmd.PersistentFlags().BoolVar(&options.obfuscate, "obfuscate", options.obfuscate, "Obfuscate sensitive information")
+	cmd.PersistentFlags().StringVarP(&options.labelSelector, "selector", "l", options.labelSelector, "Selector (label query) to filter on, supports '=', '==', and '!=")
 
 	pkgcmd.ConfigureNamespaceFlagCompletion(cmd, []string{"namespace"},
 		kubeconfigPath, impersonate, impersonateGroup, kubeContext)

pkg/k8s/api.go

@@ -490,6 +490,18 @@ func GetPodsFor(ctx context.Context, clientset kubernetes.Interface, namespace s
 
 	return pods, nil
 }
+// GetPodsBySelector queries the Kubernetes API and returns all pods in the
+// given namespace matching the provided label selector string. If selector is
+// empty, all pods in the namespace are returned.
+func GetPodsBySelector(ctx context.Context, clientset kubernetes.Interface, namespace string, selector string) ([]corev1.Pod, error) {
+	podList, err := clientset.CoreV1().Pods(namespace).List(ctx, metav1.ListOptions{
+		LabelSelector: selector,
+	})
+	if err != nil {
+		return nil, err
+	}
+	return podList.Items, nil
+}
 
 func isOwner(u types.UID, ownerRefs []metav1.OwnerReference) bool {
 	for _, or := range ownerRefs {

viz/cmd/routes.go

@@ -54,50 +54,55 @@ func NewCmdRoutes() *cobra.Command {
 	options := newRoutesOptions()
 
 	cmd := &cobra.Command{
-		Use:   "routes [flags] (RESOURCES)",
+		Use:   "routes [flags] (RESOURCE) [RESOURCE...]",
 		Short: "Display route stats",
 		Long: `Display route stats.
 
 This command will only display traffic which is sent to a service that has a Service Profile defined.`,
 		Example: `  # Routes for the webapp service in the test namespace.
   linkerd viz routes service/webapp -n test
 
+  # Routes for multiple services in the test namespace.
+  linkerd viz routes service/webapp service/api -n test
+
   # Routes for calls from the traffic deployment to the webapp service in the test namespace.
   linkerd viz routes deploy/traffic -n test --to svc/webapp`,
-		Args:      cobra.ExactArgs(1),
+		Args:      cobra.MinimumNArgs(1),
 		ValidArgs: pkgUtil.ValidTargets,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if options.namespace == "" {
 				options.namespace = pkgcmd.GetDefaultNamespace(kubeconfigPath, kubeContext)
 			}
-			req, err := buildTopRoutesRequest(args[0], options)
-			if err != nil {
-				return fmt.Errorf("error creating metrics request while making routes request: %w", err)
-			}
-
-			output, err := requestRouteStatsFromAPI(
-				api.CheckClientOrExit(hc.VizOptions{
-					Options: &healthcheck.Options{
-						ControlPlaneNamespace: controlPlaneNamespace,
-						KubeConfig:            kubeconfigPath,
-						Impersonate:           impersonate,
-						ImpersonateGroup:      impersonateGroup,
-						KubeContext:           kubeContext,
-						APIAddr:               apiAddr,
-					},
-					VizNamespaceOverride: vizNamespace,
-				}),
-				req,
-				options,
-			)
-			if err != nil {
-				fmt.Fprint(os.Stderr, err.Error())
-				os.Exit(1)
+			client := api.CheckClientOrExit(hc.VizOptions{
+				Options: &healthcheck.Options{
+					ControlPlaneNamespace: controlPlaneNamespace,
+					KubeConfig:            kubeconfigPath,
+					Impersonate:           impersonate,
+					ImpersonateGroup:      impersonateGroup,
+					KubeContext:           kubeContext,
+					APIAddr:               apiAddr,
+				},
+				VizNamespaceOverride: vizNamespace,
+			})
+
+			var buf bytes.Buffer
+			for _, arg := range args {
+				req, err := buildTopRoutesRequest(arg, options)
+				if err != nil {
+					return fmt.Errorf("error creating metrics request while making routes request: %w", err)
+				}
+
+				output, err := requestRouteStatsFromAPI(client, req, options)
+				if err != nil {
+					fmt.Fprint(os.Stderr, err.Error())
+					os.Exit(1)
+				}
+				buf.WriteString(output)
 			}
 
-			_, err = fmt.Print(output)
+			_, printErr := fmt.Print(buf.String())
 
-			return err
+			return printErr
 		},
 	}