Make CoreDNS a server type plugin for Caddy (#220)

* Make CoreDNS a server type plugin for Caddy

Remove code we don't need and port all middleware over. Fix all tests
and rework the documentation.

Also make `go generate` build a caddy binary which we then copy into
our directory. This means `go build`-builds remain working as-is.

And new etc instances in each etcd test for better isolation.
Fix more tests and rework test.Server with the newer support Caddy offers.

Fix Makefile to support new mode of operation.

middleware/kubernetes/setup.go

@@ -0,0 +1,140 @@
+package kubernetes
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/miekg/coredns/core/dnsserver"
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/middleware/kubernetes/nametemplate"
+
+	"github.com/mholt/caddy"
+	unversionedapi "k8s.io/kubernetes/pkg/api/unversioned"
+)
+
+func init() {
+	caddy.RegisterPlugin("kubernetes", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	kubernetes, err := kubernetesParse(c)
+	if err != nil {
+		return err
+	}
+
+	err = kubernetes.InitKubeCache()
+	if err != nil {
+		return err
+	}
+
+	// Register KubeCache start and stop functions with Caddy
+	c.OnStartup(func() error {
+		go kubernetes.APIConn.Run()
+		return nil
+	})
+
+	c.OnShutdown(func() error {
+		return kubernetes.APIConn.Stop()
+	})
+
+	dnsserver.GetConfig(c).AddMiddleware(func(next dnsserver.Handler) dnsserver.Handler {
+		kubernetes.Next = next
+		return kubernetes
+	})
+
+	return nil
+}
+
+func kubernetesParse(c *caddy.Controller) (Kubernetes, error) {
+	var err error
+	template := defaultNameTemplate
+
+	k8s := Kubernetes{ResyncPeriod: defaultResyncPeriod}
+	k8s.NameTemplate = new(nametemplate.NameTemplate)
+	k8s.NameTemplate.SetTemplate(template)
+
+	for c.Next() {
+		if c.Val() == "kubernetes" {
+			zones := c.RemainingArgs()
+
+			if len(zones) == 0 {
+				k8s.Zones = make([]string, len(c.ServerBlockKeys))
+				copy(k8s.Zones, c.ServerBlockKeys)
+			}
+
+			k8s.Zones = NormalizeZoneList(zones)
+			middleware.Zones(k8s.Zones).FullyQualify()
+
+			if k8s.Zones == nil || len(k8s.Zones) < 1 {
+				err = errors.New("Zone name must be provided for kubernetes middleware.")
+				return Kubernetes{}, err
+			}
+
+			for c.NextBlock() {
+				switch c.Val() {
+				case "template":
+					args := c.RemainingArgs()
+					if len(args) != 0 {
+						template := strings.Join(args, "")
+						err = k8s.NameTemplate.SetTemplate(template)
+						if err != nil {
+							return Kubernetes{}, err
+						}
+					} else {
+						return Kubernetes{}, c.ArgErr()
+					}
+				case "namespaces":
+					args := c.RemainingArgs()
+					if len(args) != 0 {
+						k8s.Namespaces = append(k8s.Namespaces, args...)
+					} else {
+						return Kubernetes{}, c.ArgErr()
+					}
+				case "endpoint":
+					args := c.RemainingArgs()
+					if len(args) != 0 {
+						k8s.APIEndpoint = args[0]
+					} else {
+						return Kubernetes{}, c.ArgErr()
+					}
+				case "resyncperiod":
+					args := c.RemainingArgs()
+					if len(args) != 0 {
+						k8s.ResyncPeriod, err = time.ParseDuration(args[0])
+						if err != nil {
+							err = errors.New(fmt.Sprintf("Unable to parse resync duration value. Value provided was '%v'. Example valid values: '15s', '5m', '1h'. Error was: %v", args[0], err))
+							return Kubernetes{}, err
+						}
+					} else {
+						return Kubernetes{}, c.ArgErr()
+					}
+				case "labels":
+					args := c.RemainingArgs()
+					if len(args) != 0 {
+						labelSelectorString := strings.Join(args, " ")
+						k8s.LabelSelector, err = unversionedapi.ParseToLabelSelector(labelSelectorString)
+						if err != nil {
+							err = errors.New(fmt.Sprintf("Unable to parse label selector. Value provided was '%v'. Error was: %v", labelSelectorString, err))
+							return Kubernetes{}, err
+						}
+					} else {
+						return Kubernetes{}, c.ArgErr()
+					}
+				}
+			}
+			return k8s, nil
+		}
+	}
+	err = errors.New("Kubernetes setup called without keyword 'kubernetes' in Corefile")
+	return Kubernetes{}, err
+}
+
+const (
+	defaultNameTemplate = "{service}.{namespace}.{zone}"
+	defaultResyncPeriod = 5 * time.Minute
+)