Refactor provider init (#360)

* Refactor provider init

This moves provider init out of vkubelet setup, instead preferring to
initialize vkubelet with a provider.

* Split API server configuration from setup.

This makes sure that configuration (which is done primarily through env
vars) is separate from actually standing up the servers.

This also makes sure to abort daemon initialization if the API servers
are not able to start.

cmd/taint.go

@@ -0,0 +1,56 @@
+package cmd
+
+import (
+	"os"
+
+	"github.com/cpuguy83/strongerrors"
+
+	"github.com/pkg/errors"
+	corev1 "k8s.io/api/core/v1"
+)
+
+// Default taint values
+const (
+	DefaultTaintEffect = corev1.TaintEffectPreferNoSchedule
+	DefaultTaintKey    = "virtual-kubelet.io/provider"
+)
+
+func getEnv(key, defaultValue string) string {
+	value, found := os.LookupEnv(key)
+	if found {
+		return value
+	}
+	return defaultValue
+}
+
+// getTaint creates a taint using the provided key/value.
+// Taint effect is read from the environment
+// The taint key/value may be overwritten by the environment.
+func getTaint(key, value string) (*corev1.Taint, error) {
+	if key == "" {
+		key = DefaultTaintKey
+		value = provider
+	}
+
+	key = getEnv("VKUBELET_TAINT_KEY", key)
+	value = getEnv("VKUBELET_TAINT_VALUE", value)
+	effectEnv := getEnv("VKUBELET_TAINT_EFFECT", string(DefaultTaintEffect))
+
+	var effect corev1.TaintEffect
+	switch effectEnv {
+	case "NoSchedule":
+		effect = corev1.TaintEffectNoSchedule
+	case "NoExecute":
+		effect = corev1.TaintEffectNoExecute
+	case "PreferNoSchedule":
+		effect = corev1.TaintEffectPreferNoSchedule
+	default:
+		return nil, strongerrors.InvalidArgument(errors.Errorf("taint effect %q is not supported", effectEnv))
+	}
+
+	return &corev1.Taint{
+		Key:    key,
+		Value:  value,
+		Effect: effect,
+	}, nil
+}