Fix crash when there are no pods matching the regex (#85)

* Removed done todo.

* Error when trying to apply tapper-daemonset with 0 pods in affinity.

* Reorder imports.

* Create/update mizu tappers if there are tapped pods. Delete if there are no tapped pods.

* Skip deletion if tapper daemonset is not installed.

* Renamed createMizuTappers -> updateMizuTappers.

* Renamed IsDaemonSetApplied -> CheckDaemonSetExists.

* Skip deletion if pod / service is not installed.

* Fixed: Inverted logic.

* Rename.

* Fixed compilation bugs.

* Warn if no pods are found. Suggest changing the namespace.

* Use consts.

* Removed empty line.

cli/cmd/tapRunner.go

@@ -3,13 +3,14 @@ package cmd
 import (
 	"context"
 	"fmt"
-	"github.com/up9inc/mizu/shared"
 	"os"
 	"os/signal"
 	"regexp"
 	"syscall"
 	"time"
 
+	"github.com/up9inc/mizu/shared"
+
 	core "k8s.io/api/core/v1"
 
 	"github.com/up9inc/mizu/cli/debounce"
@@ -45,6 +46,22 @@ func RunMizuTap(podRegexQuery *regexp.Regexp, tappingOptions *MizuTapOptions) {
 		currentlyTappedPods = matchingPods
 	}
 
+	var namespacesStr string
+	if targetNamespace != mizu.K8sAllNamespaces {
+		namespacesStr = fmt.Sprintf("namespace \"%s\"", targetNamespace)
+	} else {
+		namespacesStr = "all namespaces"
+	}
+	fmt.Printf("Tapping pods in %s\n", namespacesStr)
+
+	if len(currentlyTappedPods) == 0 {
+		var suggestionStr string
+		if targetNamespace != mizu.K8sAllNamespaces {
+			suggestionStr = "\nSelect a different namespace with -n or tap all namespaces with -A"
+		}
+		fmt.Printf("Did not find any pods matching the regex argument%s\n", suggestionStr)
+	}
+
 	nodeToTappedPodIPMap, err := getNodeHostToTappedPodIpsMap(currentlyTappedPods)
 	if err != nil {
 		return
@@ -67,7 +84,7 @@ func createMizuResources(ctx context.Context, kubernetesProvider *kubernetes.Pro
 		return err
 	}
 
-	if err := createMizuTappers(ctx, kubernetesProvider, nodeToTappedPodIPMap, tappingOptions); err != nil {
+	if err := updateMizuTappers(ctx, kubernetesProvider, nodeToTappedPodIPMap, tappingOptions); err != nil {
 		return err
 	}
 
@@ -111,7 +128,8 @@ func getMizuApiFilteringOptions(tappingOptions *MizuTapOptions) (*shared.Traffic
 	return &shared.TrafficFilteringOptions{PlainTextMaskingRegexes: compiledRegexSlice}, nil
 }
 
-func createMizuTappers(ctx context.Context, kubernetesProvider *kubernetes.Provider, nodeToTappedPodIPMap map[string][]string, tappingOptions *MizuTapOptions) error {
+func updateMizuTappers(ctx context.Context, kubernetesProvider *kubernetes.Provider, nodeToTappedPodIPMap map[string][]string, tappingOptions *MizuTapOptions) error {
+	if len(nodeToTappedPodIPMap) > 0 {
 		if err := kubernetesProvider.ApplyMizuTapperDaemonSet(
 			ctx,
 			mizu.ResourcesNamespace,
@@ -126,6 +144,12 @@ func createMizuTappers(ctx context.Context, kubernetesProvider *kubernetes.Provi
 			fmt.Printf("Error creating mizu tapper daemonset: %v\n", err)
 			return err
 		}
+	} else {
+		if err := kubernetesProvider.RemoveDaemonSet(ctx, mizu.ResourcesNamespace, mizu.TapperDaemonSetName); err != nil {
+			fmt.Printf("Error deleting mizu tapper daemonset: %v\n", err)
+			return err
+		}
+	}
 
 	return nil
 }
@@ -164,7 +188,7 @@ func watchPodsForTapping(ctx context.Context, kubernetesProvider *kubernetes.Pro
 			cancel()
 		}
 
-		if err := createMizuTappers(ctx, kubernetesProvider, nodeToTappedPodIPMap, tappingOptions); err != nil {
+		if err := updateMizuTappers(ctx, kubernetesProvider, nodeToTappedPodIPMap, tappingOptions); err != nil {
 			fmt.Printf("Error updating daemonset: %s (%v,%+v)\n", err, err, err)
 			cancel()
 		}

cli/kubernetes/provider.go

@@ -102,7 +102,6 @@ func (provider *Provider) CreateMizuAggregatorPod(ctx context.Context, namespace
 			},
 			DNSPolicy:                     core.DNSClusterFirstWithHostNet,
 			TerminationGracePeriodSeconds: new(int64),
-			// Affinity: TODO: define node selector for all relevant nodes for this mizu instance
 		},
 	}
 	//define the service account only when it exists to prevent pod crash
@@ -215,18 +214,94 @@ func (provider *Provider) CreateMizuRBAC(ctx context.Context, namespace string,
 }
 
 func (provider *Provider) RemovePod(ctx context.Context, namespace string, podName string) error {
+	if isFound, err := provider.CheckPodExists(ctx, namespace, podName);
+	err != nil {
+		return err
+	} else if !isFound {
+		return nil
+	}
+
 	return provider.clientSet.CoreV1().Pods(namespace).Delete(ctx, podName, metav1.DeleteOptions{})
 }
 
 func (provider *Provider) RemoveService(ctx context.Context, namespace string, serviceName string) error {
+	if isFound, err := provider.CheckServiceExists(ctx, namespace, serviceName);
+	err != nil {
+		return err
+	} else if !isFound {
+		return nil
+	}
+
 	return provider.clientSet.CoreV1().Services(namespace).Delete(ctx, serviceName, metav1.DeleteOptions{})
 }
 
 func (provider *Provider) RemoveDaemonSet(ctx context.Context, namespace string, daemonSetName string) error {
+	if isFound, err := provider.CheckDaemonSetExists(ctx, namespace, daemonSetName);
+	err != nil {
+		return err
+	} else if !isFound {
+		return nil
+	}
+
 	return provider.clientSet.AppsV1().DaemonSets(namespace).Delete(ctx, daemonSetName, metav1.DeleteOptions{})
 }
 
+func (provider *Provider) CheckPodExists(ctx context.Context, namespace string, name string) (bool, error) {
+	listOptions := metav1.ListOptions{
+		FieldSelector: fmt.Sprintf("metadata.name=%s", name),
+		Limit: 1,
+	}
+	resourceList, err := provider.clientSet.CoreV1().Pods(namespace).List(ctx, listOptions)
+	if err != nil {
+		return false, err
+	}
+
+	if len(resourceList.Items) > 0 {
+		return true, nil
+	}
+
+	return false, nil
+}
+
+func (provider *Provider) CheckServiceExists(ctx context.Context, namespace string, name string) (bool, error) {
+	listOptions := metav1.ListOptions{
+		FieldSelector: fmt.Sprintf("metadata.name=%s", name),
+		Limit: 1,
+	}
+	resourceList, err := provider.clientSet.CoreV1().Services(namespace).List(ctx, listOptions)
+	if err != nil {
+		return false, err
+	}
+
+	if len(resourceList.Items) > 0 {
+		return true, nil
+	}
+
+	return false, nil
+}
+
+func (provider *Provider) CheckDaemonSetExists(ctx context.Context, namespace string, name string) (bool, error) {
+	listOptions := metav1.ListOptions{
+		FieldSelector: fmt.Sprintf("metadata.name=%s", name),
+		Limit: 1,
+	}
+	resourceList, err := provider.clientSet.AppsV1().DaemonSets(namespace).List(ctx, listOptions)
+	if err != nil {
+		return false, err
+	}
+
+	if len(resourceList.Items) > 0 {
+		return true, nil
+	}
+
+	return false, nil
+}
+
 func (provider *Provider) ApplyMizuTapperDaemonSet(ctx context.Context, namespace string, daemonSetName string, podImage string, tapperPodName string, aggregatorPodIp string, nodeToTappedPodIPMap map[string][]string, linkServiceAccount bool, tapOutgoing bool) error {
+	if len(nodeToTappedPodIPMap) == 0 {
+		return fmt.Errorf("Daemon set %s must tap at least 1 pod", daemonSetName)
+	}
+
 	nodeToTappedPodIPMapJsonStr, err := json.Marshal(nodeToTappedPodIPMap)
 	if err != nil {
 		return err