Bring etcd support for bucket DNS federation

- Supports centralized `config.json`
- Supports centralized `bucket` service records
  for client lookups
- implement a new proxy forwarder

pkg/dns/coredns.go

@@ -0,0 +1,140 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * 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 dns
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/coredns/coredns/plugin/etcd/msg"
+	etcdc "github.com/coreos/etcd/client"
+)
+
+// create a new coredns service record for the bucket.
+func newCoreDNSMsg(bucket string, ip string, port int, ttl uint32) ([]byte, error) {
+	return json.Marshal(&SrvRecord{
+		Host:         ip,
+		Port:         port,
+		TTL:          ttl,
+		CreationDate: time.Now().UTC(),
+	})
+}
+
+// Retrieves list of DNS entries for a bucket.
+func (c *coreDNS) List() ([]SrvRecord, error) {
+	kapi := etcdc.NewKeysAPI(c.etcdClient)
+	key := msg.Path(fmt.Sprintf("%s.", c.domainName), defaultPrefixPath)
+	ctx, cancel := context.WithTimeout(context.Background(), defaultContextTimeout)
+	r, err := kapi.Get(ctx, key, nil)
+	cancel()
+	if err != nil {
+		return nil, err
+	}
+
+	var srvRecords []SrvRecord
+	for _, n := range r.Node.Nodes {
+		var srvRecord SrvRecord
+		if err = json.Unmarshal([]byte(n.Value), &srvRecord); err != nil {
+			return nil, err
+		}
+		srvRecord.Key = strings.TrimPrefix(n.Key, key)
+		srvRecords = append(srvRecords, srvRecord)
+	}
+	sort.Slice(srvRecords, func(i int, j int) bool {
+		return srvRecords[i].Key < srvRecords[j].Key
+	})
+	return srvRecords, nil
+}
+
+// Retrieves DNS record for a bucket.
+func (c *coreDNS) Get(bucket string) (SrvRecord, error) {
+	kapi := etcdc.NewKeysAPI(c.etcdClient)
+	key := msg.Path(fmt.Sprintf("%s.%s.", bucket, c.domainName), defaultPrefixPath)
+	ctx, cancel := context.WithTimeout(context.Background(), defaultContextTimeout)
+	r, err := kapi.Get(ctx, key, nil)
+	cancel()
+	if err != nil {
+		return SrvRecord{}, err
+	}
+	var sr SrvRecord
+	if err = json.Unmarshal([]byte(r.Node.Value), &sr); err != nil {
+		return SrvRecord{}, err
+	}
+	sr.Key = strings.TrimPrefix(r.Node.Key, key)
+	return sr, nil
+}
+
+// Adds DNS entries into etcd endpoint in CoreDNS etcd messae format.
+func (c *coreDNS) Put(bucket string) error {
+	bucketMsg, err := newCoreDNSMsg(bucket, c.domainIP, c.domainPort, defaultTTL)
+	if err != nil {
+		return err
+	}
+	kapi := etcdc.NewKeysAPI(c.etcdClient)
+	key := msg.Path(fmt.Sprintf("%s.%s.", bucket, c.domainName), defaultPrefixPath)
+	ctx, cancel := context.WithTimeout(context.Background(), defaultContextTimeout)
+	_, err = kapi.Set(ctx, key, string(bucketMsg), nil)
+	cancel()
+	return err
+}
+
+// Removes DNS entries added in Put().
+func (c *coreDNS) Delete(bucket string) error {
+	kapi := etcdc.NewKeysAPI(c.etcdClient)
+	key := msg.Path(fmt.Sprintf("%s.%s.", bucket, c.domainName), defaultPrefixPath)
+	ctx, cancel := context.WithTimeout(context.Background(), defaultContextTimeout)
+	_, err := kapi.Delete(ctx, key, nil)
+	cancel()
+	return err
+}
+
+// CoreDNS - represents dns config for coredns server.
+type coreDNS struct {
+	domainName, domainIP string
+	domainPort           int
+	etcdClient           etcdc.Client
+}
+
+// NewCoreDNS - initialize a new coreDNS set/unset values.
+func NewCoreDNS(domainName, domainIP, domainPort string, etcdClient etcdc.Client) (Config, error) {
+	if domainName == "" || domainIP == "" || etcdClient == nil {
+		return nil, errors.New("invalid argument")
+	}
+
+	if net.ParseIP(domainIP) == nil {
+		return nil, errors.New("invalid argument")
+	}
+
+	port, err := strconv.Atoi(domainPort)
+	if err != nil {
+		return nil, err
+	}
+
+	return &coreDNS{
+		domainName: domainName,
+		domainIP:   domainIP,
+		domainPort: port,
+		etcdClient: etcdClient,
+	}, nil
+}

pkg/dns/dns.go

@@ -0,0 +1,65 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * 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 dns
+
+import (
+	"time"
+)
+
+const (
+	defaultTTL            = 30
+	defaultPrefixPath     = "/skydns"
+	defaultContextTimeout = 5 * time.Minute
+)
+
+// SrvRecord - represents a DNS service record
+type SrvRecord struct {
+	Host     string `json:"host,omitempty"`
+	Port     int    `json:"port,omitempty"`
+	Priority int    `json:"priority,omitempty"`
+	Weight   int    `json:"weight,omitempty"`
+	Text     string `json:"text,omitempty"`
+	Mail     bool   `json:"mail,omitempty"` // Be an MX record. Priority becomes Preference.
+	TTL      uint32 `json:"ttl,omitempty"`
+
+	// Holds info about when the entry was created first.
+	CreationDate time.Time `json:"creationDate"`
+
+	// When a SRV record with a "Host: IP-address" is added, we synthesize
+	// a srv.Target domain name.  Normally we convert the full Key where
+	// the record lives to a DNS name and use this as the srv.Target. When
+	// TargetStrip > 0 we strip the left most TargetStrip labels from the
+	// DNS name.
+	TargetStrip int `json:"targetstrip,omitempty"`
+
+	// Group is used to group (or *not* to group) different services
+	// together. Services with an identical Group are returned in
+	// the same answer.
+	Group string `json:"group,omitempty"`
+
+	// Key carries the original key used during Put().
+	Key string `json:"-"`
+}
+
+// Config - represents dns put, get interface. This interface can be
+// used to implement various backends as needed.
+type Config interface {
+	Put(key string) error
+	List() ([]SrvRecord, error)
+	Get(key string) (SrvRecord, error)
+	Delete(key string) error
+}