The prometheus metrics refractoring (#8003)

The measures are consolidated to the following metrics

- `disk_storage_used` : Disk space used by the disk.
- `disk_storage_available`: Available disk space left on the disk.
- `disk_storage_total`: Total disk space on the disk.
- `disks_offline`: Total number of offline disks in current MinIO instance.
- `disks_total`: Total number of disks in current MinIO instance.
- `s3_requests_total`: Total number of s3 requests in current MinIO instance.
- `s3_errors_total`: Total number of errors in s3 requests in current MinIO instance.
- `s3_requests_current`: Total number of active s3 requests in current MinIO instance.
- `internode_rx_bytes_total`: Total number of internode bytes received by current MinIO server instance.
- `internode_tx_bytes_total`: Total number of bytes sent to the other nodes by current MinIO server instance.
- `s3_rx_bytes_total`: Total number of s3 bytes received by current MinIO server instance.
- `s3_tx_bytes_total`: Total number of s3 bytes sent by current MinIO server instance.
- `minio_version_info`: Current MinIO version with commit-id.
- `s3_ttfb_seconds_bucket`: Histogram that holds the latency information of the requests.

And this PR also modifies the current StorageInfo queries

- Decouples StorageInfo from ServerInfo .
- StorageInfo is enhanced to give endpoint information.

NOTE: ADMIN API VERSION IS BUMPED UP IN THIS PR

Fixes #7873

cmd/http-traffic-recorder.go

@@ -0,0 +1,107 @@
+/*
+ * MinIO Cloud Storage, (C) 2019 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 cmd
+
+import (
+	"io"
+	"net/http"
+	"time"
+)
+
+// records the incoming bytes from the underlying request.Body.
+type recordTrafficRequest struct {
+	io.ReadCloser
+	isS3Request bool
+}
+
+// Records the bytes read.
+func (r *recordTrafficRequest) Read(p []byte) (n int, err error) {
+	n, err = r.ReadCloser.Read(p)
+	globalConnStats.incInputBytes(n)
+	if r.isS3Request {
+		globalConnStats.incS3InputBytes(n)
+	}
+	return n, err
+}
+
+// Records the outgoing bytes through the responseWriter.
+type recordTrafficResponse struct {
+	// wrapper for underlying http.ResponseWriter.
+	writer      http.ResponseWriter
+	isS3Request bool
+}
+
+// Calls the underlying WriteHeader.
+func (r *recordTrafficResponse) WriteHeader(i int) {
+	r.writer.WriteHeader(i)
+}
+
+// Calls the underlying Header.
+func (r *recordTrafficResponse) Header() http.Header {
+	return r.writer.Header()
+}
+
+// Records the output bytes
+func (r *recordTrafficResponse) Write(p []byte) (n int, err error) {
+	n, err = r.writer.Write(p)
+	globalConnStats.incOutputBytes(n)
+	// Check if it is s3 request
+	if r.isS3Request {
+		globalConnStats.incS3OutputBytes(n)
+	}
+	return n, err
+}
+
+// Calls the underlying Flush.
+func (r *recordTrafficResponse) Flush() {
+	r.writer.(http.Flusher).Flush()
+}
+
+// Records the outgoing bytes through the responseWriter.
+type recordAPIStats struct {
+	// wrapper for underlying http.ResponseWriter.
+	writer         http.ResponseWriter
+	TTFB           time.Time // TimeToFirstByte.
+	firstByteRead  bool
+	respStatusCode int
+	isS3Request    bool
+}
+
+// Calls the underlying WriteHeader.
+func (r *recordAPIStats) WriteHeader(i int) {
+	r.respStatusCode = i
+	r.writer.WriteHeader(i)
+}
+
+// Calls the underlying Header.
+func (r *recordAPIStats) Header() http.Header {
+	return r.writer.Header()
+}
+
+// Records the TTFB on the first byte write.
+func (r *recordAPIStats) Write(p []byte) (n int, err error) {
+	if !r.firstByteRead {
+		r.TTFB = UTCNow()
+		r.firstByteRead = true
+	}
+	return r.writer.Write(p)
+}
+
+// Calls the underlying Flush.
+func (r *recordAPIStats) Flush() {
+	r.writer.(http.Flusher).Flush()
+}