wip: disruptors: error out if there are no targets

pkg/disruptors/pod.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"fmt"
 	"reflect"
+	"strings"
 	"time"
 
 	"github.com/grafana/xk6-disruptor/pkg/kubernetes"
@@ -52,6 +53,50 @@ type PodAttributes struct {
 	Labels map[string]string
 }
 
+// NamespaceOrDefault returns the configured namespace for this selector, and the name of the default namespace if it
+// is not configured.
+func (p PodSelector) NamespaceOrDefault() string {
+	if p.Namespace != "" {
+		return p.Namespace
+	}
+
+	return metav1.NamespaceDefault
+}
+
+// String returns a human-readable explanation of the pods matched by a PodSelector.
+func (p PodSelector) String() string {
+	var str string
+
+	if len(p.Select.Labels) == 0 && len(p.Exclude.Labels) == 0 {
+		str = "all pods"
+	} else {
+		str = "pods "
+		if len(p.Select.Labels) != 0 {
+			str += "including("
+			for k, v := range p.Select.Labels {
+				str += fmt.Sprintf("%s=%s, ", k, v)
+			}
+			str = strings.TrimSuffix(str, ", ")
+			str += "), "
+		}
+
+		if len(p.Exclude.Labels) != 0 {
+			str += "excluding("
+			for k, v := range p.Exclude.Labels {
+				str += fmt.Sprintf("%s=%s, ", k, v)
+			}
+			str = strings.TrimSuffix(str, ", ")
+			str += "), "
+		}
+
+		str = strings.TrimSuffix(str, ", ")
+	}
+
+	str += fmt.Sprintf(" in ns %q", p.NamespaceOrDefault())
+
+	return str
+}
+
 // NewPodDisruptor creates a new instance of a PodDisruptor that acts on the pods
 // that match the given PodSelector
 func NewPodDisruptor(
@@ -68,10 +113,7 @@ func NewPodDisruptor(
 	}
 
 	// ensure selector and controller use default namespace if none specified
-	namespace := selector.Namespace
-	if selector.Namespace == "" {
-		selector.Namespace = metav1.NamespaceDefault
-	}
+	namespace := selector.NamespaceOrDefault()
 	helper := k8s.PodHelper(namespace)
 
 	filter := helpers.PodFilter{
@@ -84,6 +126,10 @@ func NewPodDisruptor(
 		return nil, err
 	}
 
+	if len(targets) == 0 {
+		return nil, fmt.Errorf("couldn't find any pods matching '%s'", selector)
+	}
+
 	controller := NewAgentController(
 		ctx,
 		helper,

pkg/disruptors/pod_test.go

@@ -499,3 +499,53 @@ func Test_PodGrpcPFaultInjection(t *testing.T) {
 		})
 	}
 }
+
+func TestPodSelector_String(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name     string
+		selector PodSelector
+		expected string
+	}{
+		{
+			name:     "Empty selector",
+			expected: `all pods in ns "default"`,
+		},
+		{
+			name: "Only inclusions",
+			selector: PodSelector{
+				Namespace: "testns",
+				Select:    PodAttributes{map[string]string{"foo": "bar"}},
+			},
+			expected: `pods including(foo=bar) in ns "testns"`,
+		},
+		{
+			name: "Only exclusions",
+			selector: PodSelector{
+				Namespace: "testns",
+				Exclude:   PodAttributes{map[string]string{"foo": "bar"}},
+			},
+			expected: `pods excluding(foo=bar) in ns "testns"`,
+		},
+		{
+			name: "Both inclusions and exclusions",
+			selector: PodSelector{
+				Namespace: "testns",
+				Select:    PodAttributes{map[string]string{"foo": "bar"}},
+				Exclude:   PodAttributes{map[string]string{"boo": "baa"}},
+			},
+			expected: `pods including(foo=bar), excluding(boo=baa) in ns "testns"`,
+		},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			output := tc.selector.String()
+			if tc.expected != output {
+				t.Errorf("expected string does not match output string:\n%s\n%s", tc.expected, output)
+			}
+		})
+	}
+}

pkg/disruptors/service.go

@@ -59,6 +59,10 @@ func NewServiceDisruptor(
 		return nil, err
 	}
 
+	if len(targets) == 0 {
+		return nil, fmt.Errorf("could not find any pods backing service %q in namespace %q", service, namespace)
+	}
+
 	ph := k8s.PodHelper(namespace)
 	controller := NewAgentController(
 		ctx,