CoreDNS/SkyDNS provider

This commit adds support for CoreDNS through its etcd middleware.
Because the middleware is backward compatible with SkyDNS this
commit adds support for SkyDNS as well. In fact, new provider
is available under two names in CLI (coredns and skydns).

All interactions with middleware happen through etcd cluster,
whose location (URIs) is specified via --etcd CLI parameter
by default http://localhost:2379).

The provider translates CoreDNS/DkyDNS SRV records to
A/CNAME + optional TXT endpoints, when reading from etcd and
combines A/CNAME with TXT endpoints back into single SRV record
when writing it back.

Also:
* adds github.com/coreos/etcd package to glide.yaml and vendor folder
  because it is used by the provider
* adds "interfaces" packages and moves Registry and Provider interfaces
  declaration there. This is required in order to use registry in
  provider unit tests. Otherwise there going to be circular imports
  because provider UTests would import registry which imports providers
  back.

controller/controller.go

@@ -21,8 +21,8 @@ import (
 
 	log "github.com/Sirupsen/logrus"
 
+	"github.com/kubernetes-incubator/external-dns/interfaces"
 	"github.com/kubernetes-incubator/external-dns/plan"
-	"github.com/kubernetes-incubator/external-dns/registry"
 	"github.com/kubernetes-incubator/external-dns/source"
 )
 
@@ -34,7 +34,7 @@ import (
 // * Tell the DNS provider to apply the changes calucated by the Plan.
 type Controller struct {
 	Source   source.Source
-	Registry registry.Registry
+	Registry interfaces.Registry
 	// The policy that defines which changes to DNS records are allowed
 	Policy plan.Policy
 	// The interval between individual synchronizations

glide.yaml

@@ -54,3 +54,4 @@ import:
 - package: github.com/digitalocean/godo
   version: ~1.1.0
 - package: github.com/coreos/go-oidc
+- package: github.com/coreos/etcd

interfaces/provider.go

@@ -0,0 +1,28 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package interfaces
+
+import (
+	"github.com/kubernetes-incubator/external-dns/endpoint"
+	"github.com/kubernetes-incubator/external-dns/plan"
+)
+
+// Provider defines the interface DNS providers should implement.
+type Provider interface {
+	Records() ([]*endpoint.Endpoint, error)
+	ApplyChanges(changes *plan.Changes) error
+}

interfaces/registry.go

@@ -0,0 +1,31 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package interfaces
+
+import (
+	"github.com/kubernetes-incubator/external-dns/endpoint"
+	"github.com/kubernetes-incubator/external-dns/plan"
+)
+
+// Registry is an interface which should enables ownership concept in external-dns
+// Records() returns ALL records registered with DNS provider (TODO: for multi-zone support return all records)
+// each entry includes owner information
+// ApplyChanges(changes *plan.Changes) propagates the changes to the DNS Provider API and correspondingly updates ownership depending on type of registry being used
+type Registry interface {
+	Records() ([]*endpoint.Endpoint, error)
+	ApplyChanges(changes *plan.Changes) error
+}

main.go

@@ -33,6 +33,7 @@ import (
 	"k8s.io/client-go/tools/clientcmd"
 
 	"github.com/kubernetes-incubator/external-dns/controller"
+	"github.com/kubernetes-incubator/external-dns/interfaces"
 	"github.com/kubernetes-incubator/external-dns/pkg/apis/externaldns"
 	"github.com/kubernetes-incubator/external-dns/pkg/apis/externaldns/validation"
 	"github.com/kubernetes-incubator/external-dns/plan"
@@ -108,7 +109,7 @@ func main() {
 
 	endpointsSource := source.NewDedupSource(source.NewMultiSource(sources))
 
-	var p provider.Provider
+	var p interfaces.Provider
 	switch cfg.Provider {
 	case "aws":
 		p, err = provider.NewAWSProvider(cfg.DomainFilter, cfg.DryRun)
@@ -122,14 +123,16 @@ func main() {
 		p, err = provider.NewDigitalOceanProvider(cfg.DomainFilter, cfg.DryRun)
 	case "inmemory":
 		p, err = provider.NewInMemoryProvider(provider.InMemoryWithDomain(cfg.DomainFilter), provider.InMemoryWithLogging()), nil
+	case "coredns", "skydns":
+		p, err = provider.NewCoreDNSProvider(cfg.ETCD, cfg.DryRun)
 	default:
 		log.Fatalf("unknown dns provider: %s", cfg.Provider)
 	}
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	var r registry.Registry
+	var r interfaces.Registry
 	switch cfg.Registry {
 	case "noop":
 		r, err = registry.NewNoopRegistry(p)

pkg/apis/externaldns/types.go

@@ -49,6 +49,7 @@ type Config struct {
 	LogFormat          string
 	MetricsAddress     string
 	Debug              bool
+	ETCD               string
 }
 
 var defaultConfig = &Config{
@@ -73,6 +74,7 @@ var defaultConfig = &Config{
 	LogFormat:          "text",
 	MetricsAddress:     ":7979",
 	Debug:              false,
+	ETCD:               "http://localhost:2379",
 }
 
 // NewConfig returns new Config object
@@ -97,11 +99,12 @@ func (cfg *Config) ParseFlags(args []string) error {
 	app.Flag("compatibility", "Process annotation semantics from legacy implementations (optional, options: mate, molecule)").Default(defaultConfig.Compatibility).EnumVar(&cfg.Compatibility, "", "mate", "molecule")
 
 	// Flags related to providers
-	app.Flag("provider", "The DNS provider where the DNS records will be created (required, options: aws, google, azure, cloudflare, digitalocean, inmemory)").Required().PlaceHolder("provider").EnumVar(&cfg.Provider, "aws", "google", "azure", "cloudflare", "digitalocean", "inmemory")
+	app.Flag("provider", "The DNS provider where the DNS records will be created (required, options: aws, google, azure, cloudflare, digitalocean, inmemory, coredns, skydns)").Required().PlaceHolder("provider").EnumVar(&cfg.Provider, "aws", "google", "azure", "cloudflare", "digitalocean", "inmemory", "coredns", "skydns")
 	app.Flag("google-project", "When using the Google provider, specify the Google project (required when --provider=google)").Default(defaultConfig.GoogleProject).StringVar(&cfg.GoogleProject)
 	app.Flag("domain-filter", "Limit possible target zones by a domain suffix (optional)").Default(defaultConfig.DomainFilter).StringVar(&cfg.DomainFilter)
 	app.Flag("azure-config-file", "When using the Azure provider, specify the Azure configuration file (required when --provider=azure").Default(defaultConfig.AzureConfigFile).StringVar(&cfg.AzureConfigFile)
 	app.Flag("azure-resource-group", "When using the Azure provider, override the Azure resource group to use (optional)").Default(defaultConfig.AzureResourceGroup).StringVar(&cfg.AzureResourceGroup)
+	app.Flag("etcd", "ETCD cluster URI(s) for coredns/skydns provider").Default(defaultConfig.ETCD).StringVar(&cfg.ETCD)
 
 	// Flags related to policies
 	app.Flag("policy", "Modify how DNS records are sychronized between sources and providers (default: sync, options: sync, upsert-only)").Default(defaultConfig.Policy).EnumVar(&cfg.Policy, "sync", "upsert-only")

pkg/apis/externaldns/types_test.go

@@ -48,6 +48,7 @@ var (
 		LogFormat:          "text",
 		MetricsAddress:     ":7979",
 		Debug:              false,
+		ETCD:               "http://localhost:2379",
 	}
 
 	overriddenConfig = &Config{
@@ -72,6 +73,7 @@ var (
 		LogFormat:          "json",
 		MetricsAddress:     "127.0.0.1:9099",
 		Debug:              true,
+		ETCD:               "http://host:3378,http://host:3379",
 	}
 )
 
@@ -116,6 +118,7 @@ func TestParseFlags(t *testing.T) {
 				"--log-format=json",
 				"--metrics-address=127.0.0.1:9099",
 				"--debug",
+				"--etcd=http://host:3378,http://host:3379",
 			},
 			envVars:  map[string]string{},
 			expected: overriddenConfig,
@@ -145,6 +148,7 @@ func TestParseFlags(t *testing.T) {
 				"EXTERNAL_DNS_LOG_FORMAT":           "json",
 				"EXTERNAL_DNS_METRICS_ADDRESS":      "127.0.0.1:9099",
 				"EXTERNAL_DNS_DEBUG":                "1",
+				"EXTERNAL_DNS_ETCD":                 "http://host:3378,http://host:3379",
 			},
 			expected: overriddenConfig,
 		},