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/types.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
+}