Use random host from among multiple hosts to create requests

Also use hosts passed to Minio startup command to populate IP
addresses if MINIO_PUBLIC_IPS is not set.

pkg/dns/etcd_dns.go

@@ -0,0 +1,157 @@
+/*
+ * 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"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/minio/minio-go/pkg/set"
+
+	"github.com/coredns/coredns/plugin/etcd/msg"
+	etcd "github.com/coreos/etcd/client"
+)
+
+// ErrNoEntriesFound - Indicates no entries were found for the given key (directory)
+var ErrNoEntriesFound = errors.New("No entries found for this key")
+
+// create a new coredns service record for the bucket.
+func newCoreDNSMsg(bucket, 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 the domain.
+func (c *coreDNS) List() ([]SrvRecord, error) {
+	key := msg.Path(fmt.Sprintf("%s.", c.domainName), defaultPrefixPath)
+	return c.list(key)
+}
+
+// Retrieves DNS records for a bucket.
+func (c *coreDNS) Get(bucket string) ([]SrvRecord, error) {
+	key := msg.Path(fmt.Sprintf("%s.%s.", bucket, c.domainName), defaultPrefixPath)
+	return c.list(key)
+}
+
+// Retrieves list of entries under the key passed.
+// Note that this method fetches entries upto only two levels deep.
+func (c *coreDNS) list(key string) ([]SrvRecord, error) {
+	kapi := etcd.NewKeysAPI(c.etcdClient)
+	ctx, cancel := context.WithTimeout(context.Background(), defaultContextTimeout)
+	r, err := kapi.Get(ctx, key, &etcd.GetOptions{Recursive: true})
+	cancel()
+	if err != nil {
+		return nil, err
+	}
+
+	var srvRecords []SrvRecord
+	for _, n := range r.Node.Nodes {
+		if !n.Dir {
+			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)
+		} else {
+			// As this is a directory, loop through all the nodes inside (assuming all nodes are non-directories)
+			for _, n1 := range n.Nodes {
+				var srvRecord SrvRecord
+				if err = json.Unmarshal([]byte(n1.Value), &srvRecord); err != nil {
+					return nil, err
+				}
+				srvRecord.Key = strings.TrimPrefix(n1.Key, key)
+				srvRecord.Key = strings.TrimSuffix(srvRecord.Key, srvRecord.Host)
+				srvRecords = append(srvRecords, srvRecord)
+			}
+		}
+	}
+	if srvRecords != nil {
+		sort.Slice(srvRecords, func(i int, j int) bool {
+			return srvRecords[i].Key < srvRecords[j].Key
+		})
+	} else {
+		return nil, ErrNoEntriesFound
+	}
+	return srvRecords, nil
+}
+
+// Adds DNS entries into etcd endpoint in CoreDNS etcd message format.
+func (c *coreDNS) Put(bucket string) error {
+	var err error
+	for ip := range c.domainIPs {
+		var bucketMsg []byte
+		bucketMsg, err = newCoreDNSMsg(bucket, ip, c.domainPort, defaultTTL)
+		if err != nil {
+			return err
+		}
+		kapi := etcd.NewKeysAPI(c.etcdClient)
+		key := msg.Path(fmt.Sprintf("%s.%s", bucket, c.domainName), defaultPrefixPath)
+		key = key + "/" + ip
+		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 := etcd.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, &etcd.DeleteOptions{Recursive: true})
+	cancel()
+	return err
+}
+
+// CoreDNS - represents dns config for coredns server.
+type coreDNS struct {
+	domainName string
+	domainIPs  set.StringSet
+	domainPort int
+	etcdClient etcd.Client
+}
+
+// NewCoreDNS - initialize a new coreDNS set/unset values.
+func NewCoreDNS(domainName string, domainIPs set.StringSet, domainPort string, etcdClient etcd.Client) (Config, error) {
+	if domainName == "" || domainIPs.IsEmpty() || etcdClient == nil {
+		return nil, errors.New("invalid argument")
+	}
+
+	port, err := strconv.Atoi(domainPort)
+	if err != nil {
+		return nil, err
+	}
+
+	return &coreDNS{
+		domainName: domainName,
+		domainIPs:  domainIPs,
+		domainPort: port,
+		etcdClient: etcdClient,
+	}, nil
+}