Bring etcd support for bucket DNS federation

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

cmd/generic-handlers.go

@@ -19,13 +19,17 @@ package cmd
 import (
 	"bufio"
 	"context"
+	"fmt"
 	"net"
 	"net/http"
+	"net/url"
 	"strings"
 	"time"
 
+	"github.com/coreos/etcd/client"
 	humanize "github.com/dustin/go-humanize"
 	"github.com/minio/minio/cmd/logger"
+	"github.com/minio/minio/pkg/handlers"
 	"github.com/minio/minio/pkg/sys"
 	"github.com/rs/cors"
 	"golang.org/x/time/rate"
@@ -611,6 +615,64 @@ func (h pathValidityHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	h.handler.ServeHTTP(w, r)
 }
 
+// To forward the path style requests on a bucket to the right
+// configured server, bucket to IP configuration is obtained
+// from centralized etcd configuration service.
+type bucketForwardingHandler struct {
+	fwd     *handlers.Forwarder
+	handler http.Handler
+}
+
+func (f bucketForwardingHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if globalDNSConfig == nil || globalDomainName == "" {
+		f.handler.ServeHTTP(w, r)
+		return
+	}
+
+	bucket, object := urlPath2BucketObjectName(r.URL.Path)
+	if r.Method == http.MethodPut && bucket != "" && object == "" {
+		f.handler.ServeHTTP(w, r)
+		return
+	}
+
+	sr, err := globalDNSConfig.Get(bucket)
+	if err != nil {
+		if client.IsKeyNotFound(err) {
+			writeErrorResponse(w, ErrNoSuchBucket, r.URL)
+		} else {
+			writeErrorResponse(w, toAPIErrorCode(err), r.URL)
+		}
+		return
+	}
+
+	if sr.Host != globalDomainIP {
+		backendURL := fmt.Sprintf("http://%s:%d", sr.Host, sr.Port)
+		if globalIsSSL {
+			backendURL = fmt.Sprintf("https://%s:%d", sr.Host, sr.Port)
+		}
+		r.URL, err = url.Parse(backendURL)
+		if err != nil {
+			writeErrorResponse(w, toAPIErrorCode(err), r.URL)
+			return
+		}
+		f.fwd.ServeHTTP(w, r)
+		return
+	}
+
+	f.handler.ServeHTTP(w, r)
+}
+
+// setBucketForwardingHandler middleware forwards the path style requests
+// on a bucket to the right bucket location, bucket to IP configuration
+// is obtained from centralized etcd configuration service.
+func setBucketForwardingHandler(h http.Handler) http.Handler {
+	fwd := handlers.NewForwarder(&handlers.Forwarder{
+		PassHost:     true,
+		RoundTripper: NewCustomHTTPTransport(),
+	})
+	return bucketForwardingHandler{fwd, h}
+}
+
 // setRateLimitHandler middleware limits the throughput to h using a
 // rate.Limiter token bucket configured with maxOpenFileLimit and
 // burst set to 1. The request will idle for up to 1*time.Second.