Adds conditions for clusters that do not have Sourcegraph installed. (#951)

- Before, clusters/namespaces would pass all validations even if no
  Sourcegraph instance was installed.
- Now: pods, services, connections and PVC validations fail with a
  warning if none exist.

Author: jasonhawkharris

internal/validate/kube/kube.go

@@ -211,6 +211,18 @@ func Pods(ctx context.Context, config *Config) ([]validate.Result, error) {
 
 	var results []validate.Result
 
+	if len(pods.Items) == 0 {
+		results = append(results, validate.Result{
+			Status: validate.Warning,
+			Message: fmt.Sprintf(
+				"No pods exist on namespace '%s'. check namespace/cluster",
+				config.namespace,
+			),
+		})
+
+		return results, nil
+	}
+
 	for _, pod := range pods.Items {
 		r := validatePod(&pod)
 		results = append(results, r...)
@@ -291,6 +303,18 @@ func Services(ctx context.Context, config *Config) ([]validate.Result, error) {
 
 	var results []validate.Result
 
+	if len(services.Items) <= 1 {
+		results = append(results, validate.Result{
+			Status: validate.Warning,
+			Message: fmt.Sprintf(
+				"unexpected number of services on namespace '%s'; check namespace/cluster",
+				config.namespace,
+			),
+		})
+
+		return results, nil
+	}
+
 	for _, service := range services.Items {
 		r := validateService(&service)
 		results = append(results, r...)
@@ -326,6 +350,18 @@ func PVCs(ctx context.Context, config *Config) ([]validate.Result, error) {
 
 	var results []validate.Result
 
+	if len(pvcs.Items) == 0 {
+		results = append(results, validate.Result{
+			Status: validate.Warning,
+			Message: fmt.Sprintf(
+				"no PVCs exist in namespace '%s'; check namespace/cluster",
+				config.namespace,
+			),
+		})
+
+		return results, nil
+	}
+
 	for _, pvc := range pvcs.Items {
 		r := validatePVC(&pvc)
 		results = append(results, r...)
@@ -368,6 +404,18 @@ func Connections(ctx context.Context, config *Config) ([]validate.Result, error)
 		return nil, err
 	}
 
+	if len(pods.Items) == 0 {
+		results = append(results, validate.Result{
+			Status: validate.Warning,
+			Message: fmt.Sprintf(
+				"cannot check connections: zero pods exist in namespace '%s'",
+				config.namespace,
+			),
+		})
+
+		return results, nil
+	}
+
 	// iterate through pods looking for specific pod name prefixes, then construct
 	// a relationship map between pods that should have connectivity with each other
 	for _, pod := range pods.Items {