minio/cmd/metrics-v2.go

// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cmd

import (
	"context"
	"fmt"
	"net/http"
	"runtime"
	"strings"
	"sync"
	"time"

	"github.com/minio/minio/cmd/logger"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	dto "github.com/prometheus/client_model/go"
	"github.com/prometheus/procfs"
)

// MetricNamespace is top level grouping of metrics to create the metric name.
type MetricNamespace string

// MetricSubsystem is the sub grouping for metrics within a namespace.
type MetricSubsystem string

const (
	bucketMetricNamespace    MetricNamespace = "minio_bucket"
	clusterMetricNamespace   MetricNamespace = "minio_cluster"
	healMetricNamespace      MetricNamespace = "minio_heal"
	interNodeMetricNamespace MetricNamespace = "minio_inter_node"
	nodeMetricNamespace      MetricNamespace = "minio_node"
	minioMetricNamespace     MetricNamespace = "minio"
	s3MetricNamespace        MetricNamespace = "minio_s3"
)

const (
	cacheSubsystem            MetricSubsystem = "cache"
	capacityRawSubsystem      MetricSubsystem = "capacity_raw"
	capacityUsableSubsystem   MetricSubsystem = "capacity_usable"
	diskSubsystem             MetricSubsystem = "disk"
	fileDescriptorSubsystem   MetricSubsystem = "file_descriptor"
	goRoutines                MetricSubsystem = "go_routine"
	ioSubsystem               MetricSubsystem = "io"
	nodesSubsystem            MetricSubsystem = "nodes"
	objectsSubsystem          MetricSubsystem = "objects"
	processSubsystem          MetricSubsystem = "process"
	replicationSubsystem      MetricSubsystem = "replication"
	requestsSubsystem         MetricSubsystem = "requests"
	requestsRejectedSubsystem MetricSubsystem = "requests_rejected"
	timeSubsystem             MetricSubsystem = "time"
	trafficSubsystem          MetricSubsystem = "traffic"
	softwareSubsystem         MetricSubsystem = "software"
	sysCallSubsystem          MetricSubsystem = "syscall"
	usageSubsystem            MetricSubsystem = "usage"
)

// MetricName are the individual names for the metric.
type MetricName string

const (
	authTotal      MetricName = "auth_total"
	canceledTotal  MetricName = "canceled_total"
	errorsTotal    MetricName = "errors_total"
	headerTotal    MetricName = "header_total"
	healTotal      MetricName = "heal_total"
	hitsTotal      MetricName = "hits_total"
	inflightTotal  MetricName = "inflight_total"
	invalidTotal   MetricName = "invalid_total"
	limitTotal     MetricName = "limit_total"
	missedTotal    MetricName = "missed_total"
	waitingTotal   MetricName = "waiting_total"
	objectTotal    MetricName = "object_total"
	offlineTotal   MetricName = "offline_total"
	onlineTotal    MetricName = "online_total"
	openTotal      MetricName = "open_total"
	readTotal      MetricName = "read_total"
	timestampTotal MetricName = "timestamp_total"
	writeTotal     MetricName = "write_total"
	total          MetricName = "total"
	freeInodes     MetricName = "free_inodes"

	failedCount   MetricName = "failed_count"
	failedBytes   MetricName = "failed_bytes"
	freeBytes     MetricName = "free_bytes"
	pendingBytes  MetricName = "pending_bytes"
	pendingCount  MetricName = "pending_count"
	readBytes     MetricName = "read_bytes"
	rcharBytes    MetricName = "rchar_bytes"
	receivedBytes MetricName = "received_bytes"
	sentBytes     MetricName = "sent_bytes"
	totalBytes    MetricName = "total_bytes"
	usedBytes     MetricName = "used_bytes"
	writeBytes    MetricName = "write_bytes"
	wcharBytes    MetricName = "wchar_bytes"

	usagePercent MetricName = "update_percent"

	commitInfo  MetricName = "commit_info"
	usageInfo   MetricName = "usage_info"
	versionInfo MetricName = "version_info"

	sizeDistribution = "size_distribution"
	ttfbDistribution = "ttfb_seconds_distribution"

	lastActivityTime = "last_activity_nano_seconds"
	startTime        = "starttime_seconds"
	upTime           = "uptime_seconds"
	memory           = "resident_memory_bytes"
	cpu              = "cpu_total_seconds"
)

const (
	serverName = "server"
)

// MetricType for the types of metrics supported
type MetricType string

const (
	gaugeMetric     = "gaugeMetric"
	counterMetric   = "counterMetric"
	histogramMetric = "histogramMetric"
)

// MetricDescription describes the metric
type MetricDescription struct {
	Namespace MetricNamespace `json:"MetricNamespace"`
	Subsystem MetricSubsystem `json:"Subsystem"`
	Name      MetricName      `json:"MetricName"`
	Help      string          `json:"Help"`
	Type      MetricType      `json:"Type"`
}

// Metric captures the details for a metric
type Metric struct {
	Description          MetricDescription `json:"Description"`
	StaticLabels         map[string]string `json:"StaticLabels"`
	Value                float64           `json:"Value"`
	VariableLabels       map[string]string `json:"VariableLabels"`
	HistogramBucketLabel string            `json:"HistogramBucketLabel"`
	Histogram            map[string]uint64 `json:"Histogram"`
}

func (m *Metric) copyMetric() Metric {
	metric := Metric{
		Description:          m.Description,
		Value:                m.Value,
		HistogramBucketLabel: m.HistogramBucketLabel,
		StaticLabels:         make(map[string]string),
		VariableLabels:       make(map[string]string),
		Histogram:            make(map[string]uint64),
	}
	for k, v := range m.StaticLabels {
		metric.StaticLabels[k] = v
	}
	for k, v := range m.VariableLabels {
		metric.VariableLabels[k] = v
	}
	for k, v := range m.Histogram {
		metric.Histogram[k] = v
	}
	return metric
}

// MetricsGroup are a group of metrics that are initialized together.
type MetricsGroup struct {
	id            string
	cacheInterval time.Duration
	cachedRead    func(ctx context.Context, mg *MetricsGroup) []Metric
	read          func(ctx context.Context) []Metric
}

var metricsGroupCache = make(map[string]*timedValue)
var cacheLock sync.Mutex

func cachedRead(ctx context.Context, mg *MetricsGroup) (metrics []Metric) {
	cacheLock.Lock()
	defer cacheLock.Unlock()
	v, ok := metricsGroupCache[mg.id]
	if !ok {
		interval := mg.cacheInterval
		if interval == 0 {
			interval = 30 * time.Second
		}
		v = &timedValue{}
		v.Once.Do(func() {
			v.Update = func() (interface{}, error) {
				c := mg.read(ctx)
				return c, nil
			}
			v.TTL = interval
		})
		metricsGroupCache[mg.id] = v
	}
	c, err := v.Get()
	if err != nil {
		return []Metric{}
	}
	m := c.([]Metric)
	for i := range m {
		metrics = append(metrics, m[i].copyMetric())
	}
	return metrics
}

// MetricsGenerator are functions that generate metric groups.
type MetricsGenerator func() MetricsGroup

// GetGlobalGenerators gets all the generators the report global metrics pre calculated.
func GetGlobalGenerators() []MetricsGenerator {
	g := []MetricsGenerator{
		getBucketUsageMetrics,
		getMinioHealingMetrics,
		getNodeHealthMetrics,
		getClusterStorageMetrics,
	}
	return g
}

// GetAllGenerators gets all the metric generators.
func GetAllGenerators() []MetricsGenerator {
	g := GetGlobalGenerators()
	g = append(g, GetGeneratorsForPeer()...)
	return g
}

// GetGeneratorsForPeer - gets the generators to report to peer.
func GetGeneratorsForPeer() []MetricsGenerator {
	g := []MetricsGenerator{
		getCacheMetrics,
		getGoMetrics,
		getHTTPMetrics,
		getLocalStorageMetrics,
		getMinioProcMetrics,
		getMinioVersionMetrics,
		getNetworkMetrics,
		getS3TTFBMetric,
	}
	return g
}

// GetSingleNodeGenerators gets the metrics that are local
func GetSingleNodeGenerators() []MetricsGenerator {
	g := []MetricsGenerator{
		getNodeHealthMetrics,
		getCacheMetrics,
		getHTTPMetrics,
		getNetworkMetrics,
		getMinioVersionMetrics,
		getS3TTFBMetric,
	}
	return g
}

func getClusterCapacityTotalBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: capacityRawSubsystem,
		Name:      totalBytes,
		Help:      "Total capacity online in the cluster.",
		Type:      gaugeMetric,
	}
}
func getClusterCapacityFreeBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: capacityRawSubsystem,
		Name:      freeBytes,
		Help:      "Total free capacity online in the cluster.",
		Type:      gaugeMetric,
	}
}
func getClusterCapacityUsageBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: capacityUsableSubsystem,
		Name:      totalBytes,
		Help:      "Total usable capacity online in the cluster.",
		Type:      gaugeMetric,
	}
}
func getClusterCapacityUsageFreeBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: capacityUsableSubsystem,
		Name:      freeBytes,
		Help:      "Total free usable capacity online in the cluster.",
		Type:      gaugeMetric,
	}
}

func getNodeDiskUsedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: diskSubsystem,
		Name:      usedBytes,
		Help:      "Total storage used on a disk.",
		Type:      gaugeMetric,
	}
}
func getNodeDiskFreeBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: diskSubsystem,
		Name:      freeBytes,
		Help:      "Total storage available on a disk.",
		Type:      gaugeMetric,
	}
}
func getClusterDisksOfflineTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: diskSubsystem,
		Name:      offlineTotal,
		Help:      "Total disks offline.",
		Type:      gaugeMetric,
	}
}

func getClusterDisksOnlineTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: diskSubsystem,
		Name:      onlineTotal,
		Help:      "Total disks online.",
		Type:      gaugeMetric,
	}
}

func getClusterDisksTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: diskSubsystem,
		Name:      total,
		Help:      "Total disks.",
		Type:      gaugeMetric,
	}
}

func getClusterDisksFreeInodes() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: diskSubsystem,
		Name:      freeInodes,
		Help:      "Total free inodes.",
		Type:      gaugeMetric,
	}
}

func getNodeDiskTotalBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: diskSubsystem,
		Name:      totalBytes,
		Help:      "Total storage on a disk.",
		Type:      gaugeMetric,
	}
}
func getUsageLastScanActivityMD() MetricDescription {
	return MetricDescription{
		Namespace: minioMetricNamespace,
		Subsystem: usageSubsystem,
		Name:      lastActivityTime,
		Help:      "Time elapsed (in nano seconds) since last scan activity. This is set to 0 until first scan cycle",
		Type:      gaugeMetric,
	}
}

func getBucketUsageTotalBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: usageSubsystem,
		Name:      totalBytes,
		Help:      "Total bucket size in bytes",
		Type:      gaugeMetric,
	}
}
func getBucketUsageObjectsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: usageSubsystem,
		Name:      objectTotal,
		Help:      "Total number of objects",
		Type:      gaugeMetric,
	}
}
func getBucketRepPendingBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: replicationSubsystem,
		Name:      pendingBytes,
		Help:      "Total bytes pending to replicate.",
		Type:      gaugeMetric,
	}
}
func getBucketRepFailedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: replicationSubsystem,
		Name:      failedBytes,
		Help:      "Total number of bytes failed at least once to replicate.",
		Type:      gaugeMetric,
	}
}
func getBucketRepSentBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: replicationSubsystem,
		Name:      sentBytes,
		Help:      "Total number of bytes replicated to the target bucket.",
		Type:      gaugeMetric,
	}
}
func getBucketRepReceivedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: replicationSubsystem,
		Name:      receivedBytes,
		Help:      "Total number of bytes replicated to this bucket from another source bucket.",
		Type:      gaugeMetric,
	}
}
func getBucketRepPendingOperationsMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: replicationSubsystem,
		Name:      pendingCount,
		Help:      "Total number of objects pending replication",
		Type:      gaugeMetric,
	}
}
func getBucketRepFailedOperationsMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: replicationSubsystem,
		Name:      failedCount,
		Help:      "Total number of objects which failed replication",
		Type:      gaugeMetric,
	}
}
func getBucketObjectDistributionMD() MetricDescription {
	return MetricDescription{
		Namespace: bucketMetricNamespace,
		Subsystem: objectsSubsystem,
		Name:      sizeDistribution,
		Help:      "Distribution of object sizes in the bucket, includes label for the bucket name.",
		Type:      histogramMetric,
	}
}
func getInternodeFailedRequests() MetricDescription {
	return MetricDescription{
		Namespace: interNodeMetricNamespace,
		Subsystem: trafficSubsystem,
		Name:      errorsTotal,
		Help:      "Total number of failed internode calls.",
		Type:      counterMetric,
	}
}

func getInterNodeSentBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: interNodeMetricNamespace,
		Subsystem: trafficSubsystem,
		Name:      sentBytes,
		Help:      "Total number of bytes sent to the other peer nodes.",
		Type:      counterMetric,
	}
}
func getInterNodeReceivedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: interNodeMetricNamespace,
		Subsystem: trafficSubsystem,
		Name:      receivedBytes,
		Help:      "Total number of bytes received from other peer nodes.",
		Type:      counterMetric,
	}
}
func getS3SentBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: trafficSubsystem,
		Name:      sentBytes,
		Help:      "Total number of s3 bytes sent",
		Type:      counterMetric,
	}
}
func getS3ReceivedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: trafficSubsystem,
		Name:      receivedBytes,
		Help:      "Total number of s3 bytes received.",
		Type:      counterMetric,
	}
}
func getS3RequestsInFlightMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsSubsystem,
		Name:      inflightTotal,
		Help:      "Total number of S3 requests currently in flight",
		Type:      gaugeMetric,
	}
}
func getS3RequestsInQueueMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsSubsystem,
		Name:      waitingTotal,
		Help:      "Number of S3 requests in the waiting queue",
		Type:      gaugeMetric,
	}
}
func getS3RequestsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsSubsystem,
		Name:      total,
		Help:      "Total number S3 requests",
		Type:      counterMetric,
	}
}
func getS3RequestsErrorsMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsSubsystem,
		Name:      errorsTotal,
		Help:      "Total number S3 requests with errors",
		Type:      counterMetric,
	}
}
func getS3RequestsCanceledMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsSubsystem,
		Name:      canceledTotal,
		Help:      "Total number S3 requests that were canceled from the client while processing",
		Type:      counterMetric,
	}
}
func getS3RejectedAuthRequestsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsRejectedSubsystem,
		Name:      authTotal,
		Help:      "Total number S3 requests rejected for auth failure.",
		Type:      counterMetric,
	}
}
func getS3RejectedHeaderRequestsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsRejectedSubsystem,
		Name:      headerTotal,
		Help:      "Total number S3 requests rejected for invalid header.",
		Type:      counterMetric,
	}
}
func getS3RejectedTimestampRequestsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsRejectedSubsystem,
		Name:      timestampTotal,
		Help:      "Total number S3 requests rejected for invalid timestamp.",
		Type:      counterMetric,
	}
}
func getS3RejectedInvalidRequestsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: requestsRejectedSubsystem,
		Name:      invalidTotal,
		Help:      "Total number S3 invalid requests.",
		Type:      counterMetric,
	}
}
func getCacheHitsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: minioNamespace,
		Subsystem: cacheSubsystem,
		Name:      hitsTotal,
		Help:      "Total number of disk cache hits",
		Type:      counterMetric,
	}
}
func getCacheHitsMissedTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: minioNamespace,
		Subsystem: cacheSubsystem,
		Name:      missedTotal,
		Help:      "Total number of disk cache misses",
		Type:      counterMetric,
	}
}
func getCacheUsagePercentMD() MetricDescription {
	return MetricDescription{
		Namespace: minioNamespace,
		Subsystem: minioNamespace,
		Name:      usagePercent,
		Help:      "Total percentage cache usage",
		Type:      gaugeMetric,
	}
}
func getCacheUsageInfoMD() MetricDescription {
	return MetricDescription{
		Namespace: minioNamespace,
		Subsystem: cacheSubsystem,
		Name:      usageInfo,
		Help:      "Total percentage cache usage, value of 1 indicates high and 0 low, label level is set as well",
		Type:      gaugeMetric,
	}
}
func getCacheUsedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: minioNamespace,
		Subsystem: cacheSubsystem,
		Name:      usedBytes,
		Help:      "Current cache usage in bytes",
		Type:      gaugeMetric,
	}
}
func getCacheTotalBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: minioNamespace,
		Subsystem: cacheSubsystem,
		Name:      totalBytes,
		Help:      "Total size of cache disk in bytes",
		Type:      gaugeMetric,
	}
}
func getCacheSentBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: minioNamespace,
		Subsystem: cacheSubsystem,
		Name:      sentBytes,
		Help:      "Total number of bytes served from cache",
		Type:      counterMetric,
	}
}
func getHealObjectsTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: healMetricNamespace,
		Subsystem: objectsSubsystem,
		Name:      total,
		Help:      "Objects scanned in current self healing run",
		Type:      gaugeMetric,
	}
}
func getHealObjectsHealTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: healMetricNamespace,
		Subsystem: objectsSubsystem,
		Name:      healTotal,
		Help:      "Objects healed in current self healing run",
		Type:      gaugeMetric,
	}
}

func getHealObjectsFailTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: healMetricNamespace,
		Subsystem: objectsSubsystem,
		Name:      errorsTotal,
		Help:      "Objects for which healing failed in current self healing run",
		Type:      gaugeMetric,
	}
}
func getHealLastActivityTimeMD() MetricDescription {
	return MetricDescription{
		Namespace: healMetricNamespace,
		Subsystem: timeSubsystem,
		Name:      lastActivityTime,
		Help:      "Time elapsed (in nano seconds) since last self healing activity. This is set to -1 until initial self heal activity",
		Type:      gaugeMetric,
	}
}
func getNodeOnlineTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: nodesSubsystem,
		Name:      onlineTotal,
		Help:      "Total number of MinIO nodes online.",
		Type:      gaugeMetric,
	}
}
func getNodeOfflineTotalMD() MetricDescription {
	return MetricDescription{
		Namespace: clusterMetricNamespace,
		Subsystem: nodesSubsystem,
		Name:      offlineTotal,
		Help:      "Total number of MinIO nodes offline.",
		Type:      gaugeMetric,
	}
}
func getMinIOVersionMD() MetricDescription {
	return MetricDescription{
		Namespace: minioMetricNamespace,
		Subsystem: softwareSubsystem,
		Name:      versionInfo,
		Help:      "MinIO Release tag for the server",
		Type:      gaugeMetric,
	}
}
func getMinIOCommitMD() MetricDescription {
	return MetricDescription{
		Namespace: minioMetricNamespace,
		Subsystem: softwareSubsystem,
		Name:      commitInfo,
		Help:      "Git commit hash for the MinIO release.",
		Type:      gaugeMetric,
	}
}
func getS3TTFBDistributionMD() MetricDescription {
	return MetricDescription{
		Namespace: s3MetricNamespace,
		Subsystem: timeSubsystem,
		Name:      ttfbDistribution,
		Help:      "Distribution of the time to first byte across API calls.",
		Type:      gaugeMetric,
	}
}
func getMinioFDOpenMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: fileDescriptorSubsystem,
		Name:      openTotal,
		Help:      "Total number of open file descriptors by the MinIO Server process.",
		Type:      gaugeMetric,
	}
}
func getMinioFDLimitMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: fileDescriptorSubsystem,
		Name:      limitTotal,
		Help:      "Limit on total number of open file descriptors for the MinIO Server process.",
		Type:      gaugeMetric,
	}
}
func getMinioProcessIOWriteBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: ioSubsystem,
		Name:      writeBytes,
		Help:      "Total bytes written by the process to the underlying storage system, /proc/[pid]/io write_bytes",
		Type:      counterMetric,
	}
}
func getMinioProcessIOReadBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: ioSubsystem,
		Name:      readBytes,
		Help:      "Total bytes read by the process from the underlying storage system, /proc/[pid]/io read_bytes",
		Type:      counterMetric,
	}
}
func getMinioProcessIOWriteCachedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: ioSubsystem,
		Name:      wcharBytes,
		Help:      "Total bytes written by the process to the underlying storage system including page cache, /proc/[pid]/io wchar",
		Type:      counterMetric,
	}
}
func getMinioProcessIOReadCachedBytesMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: ioSubsystem,
		Name:      rcharBytes,
		Help:      "Total bytes read by the process from the underlying storage system including cache, /proc/[pid]/io rchar",
		Type:      counterMetric,
	}
}
func getMinIOProcessSysCallRMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: sysCallSubsystem,
		Name:      readTotal,
		Help:      "Total read SysCalls to the kernel. /proc/[pid]/io syscr",
		Type:      counterMetric,
	}
}
func getMinIOProcessSysCallWMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: sysCallSubsystem,
		Name:      writeTotal,
		Help:      "Total write SysCalls to the kernel. /proc/[pid]/io syscw",
		Type:      counterMetric,
	}
}
func getMinIOGORoutineCountMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: goRoutines,
		Name:      total,
		Help:      "Total number of go routines running.",
		Type:      gaugeMetric,
	}
}
func getMinIOProcessStartTimeMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: processSubsystem,
		Name:      startTime,
		Help:      "Start time for MinIO process per node, time in seconds since Unix epoc.",
		Type:      gaugeMetric,
	}
}
func getMinIOProcessUptimeMD() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: processSubsystem,
		Name:      upTime,
		Help:      "Uptime for MinIO process per node in seconds.",
		Type:      gaugeMetric,
	}
}
func getMinIOProcessResidentMemory() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: processSubsystem,
		Name:      memory,
		Help:      "Resident memory size in bytes.",
		Type:      gaugeMetric,
	}
}
func getMinIOProcessCPUTime() MetricDescription {
	return MetricDescription{
		Namespace: nodeMetricNamespace,
		Subsystem: processSubsystem,
		Name:      cpu,
		Help:      "Total user and system CPU time spent in seconds.",
		Type:      counterMetric,
	}
}
func getMinioProcMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "MinioProcMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			if runtime.GOOS == "windows" {
				return nil
			}
			metrics = make([]Metric, 0, 20)
			p, err := procfs.Self()
			if err != nil {
				logger.LogOnceIf(ctx, err, nodeMetricNamespace)
				return
			}
			var openFDs int
			openFDs, err = p.FileDescriptorsLen()
			if err != nil {
				logger.LogOnceIf(ctx, err, getMinioFDOpenMD())
				return
			}
			l, err := p.Limits()
			if err != nil {
				logger.LogOnceIf(ctx, err, getMinioFDLimitMD())
				return
			}
			io, err := p.IO()
			if err != nil {
				logger.LogOnceIf(ctx, err, ioSubsystem)
				return
			}
			stat, err := p.Stat()
			if err != nil {
				logger.LogOnceIf(ctx, err, processSubsystem)
				return
			}
			startTime, err := stat.StartTime()
			if err != nil {
				logger.LogOnceIf(ctx, err, startTime)
				return
			}

			metrics = append(metrics,
				Metric{
					Description: getMinioFDOpenMD(),
					Value:       float64(openFDs),
				},
			)
			metrics = append(metrics,
				Metric{
					Description: getMinioFDLimitMD(),
					Value:       float64(l.OpenFiles),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinIOProcessSysCallRMD(),
					Value:       float64(io.SyscR),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinIOProcessSysCallWMD(),
					Value:       float64(io.SyscW),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinioProcessIOReadBytesMD(),
					Value:       float64(io.ReadBytes),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinioProcessIOWriteBytesMD(),
					Value:       float64(io.WriteBytes),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinioProcessIOReadCachedBytesMD(),
					Value:       float64(io.RChar),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinioProcessIOWriteCachedBytesMD(),
					Value:       float64(io.WChar),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinIOProcessStartTimeMD(),
					Value:       startTime,
				})
			metrics = append(metrics,
				Metric{
					Description: getMinIOProcessUptimeMD(),
					Value:       time.Since(globalBootTime).Seconds(),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinIOProcessResidentMemory(),
					Value:       float64(stat.ResidentMemory()),
				})
			metrics = append(metrics,
				Metric{
					Description: getMinIOProcessCPUTime(),
					Value:       float64(stat.CPUTime()),
				})
			return
		},
	}
}
func getGoMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "GoMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			metrics = append(metrics, Metric{
				Description: getMinIOGORoutineCountMD(),
				Value:       float64(runtime.NumGoroutine()),
			})
			return
		},
	}
}
func getS3TTFBMetric() MetricsGroup {
	return MetricsGroup{
		id:         "s3TTFBMetric",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {

			// Read prometheus metric on this channel
			ch := make(chan prometheus.Metric)
			var wg sync.WaitGroup
			wg.Add(1)

			// Read prometheus histogram data and convert it to internal metric data
			go func() {
				defer wg.Done()
				for promMetric := range ch {
					dtoMetric := &dto.Metric{}
					err := promMetric.Write(dtoMetric)
					if err != nil {
						logger.LogIf(GlobalContext, err)
						return
					}
					h := dtoMetric.GetHistogram()
					for _, b := range h.Bucket {
						labels := make(map[string]string)
						for _, lp := range dtoMetric.GetLabel() {
							labels[*lp.Name] = *lp.Value
						}
						labels["le"] = fmt.Sprintf("%.3f", *b.UpperBound)
						metric := Metric{
							Description:    getS3TTFBDistributionMD(),
							VariableLabels: labels,
							Value:          float64(b.GetCumulativeCount()),
						}
						metrics = append(metrics, metric)
					}
				}

			}()

			httpRequestsDuration.Collect(ch)
			close(ch)
			wg.Wait()
			return
		},
	}
}

func getMinioVersionMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "MinioVersionMetrics",
		cachedRead: cachedRead,
		read: func(_ context.Context) (metrics []Metric) {
			metrics = append(metrics, Metric{
				Description:    getMinIOCommitMD(),
				VariableLabels: map[string]string{"commit": CommitID},
			})
			metrics = append(metrics, Metric{
				Description:    getMinIOVersionMD(),
				VariableLabels: map[string]string{"version": Version},
			})
			return
		},
	}
}

func getNodeHealthMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "NodeHealthMetrics",
		cachedRead: cachedRead,
		read: func(_ context.Context) (metrics []Metric) {
			nodesUp, nodesDown := GetPeerOnlineCount()
			metrics = append(metrics, Metric{
				Description: getNodeOnlineTotalMD(),
				Value:       float64(nodesUp),
			})
			metrics = append(metrics, Metric{
				Description: getNodeOfflineTotalMD(),
				Value:       float64(nodesDown),
			})
			return
		},
	}
}

func getMinioHealingMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "minioHealingMetrics",
		cachedRead: cachedRead,
		read: func(_ context.Context) (metrics []Metric) {
			metrics = make([]Metric, 0, 5)
			if !globalIsErasure {
				return
			}
			bgSeq, exists := globalBackgroundHealState.getHealSequenceByToken(bgHealingUUID)
			if !exists {
				return
			}

			if bgSeq.lastHealActivity.IsZero() {
				return
			}

			metrics = append(metrics, Metric{
				Description: getHealLastActivityTimeMD(),
				Value:       float64(time.Since(bgSeq.lastHealActivity)),
			})
			metrics = append(metrics, getObjectsScanned(bgSeq)...)
			metrics = append(metrics, getScannedItems(bgSeq)...)
			metrics = append(metrics, getFailedItems(bgSeq)...)
			return
		},
	}
}

func getFailedItems(seq *healSequence) (m []Metric) {
	m = make([]Metric, 0, 1)
	for k, v := range seq.gethealFailedItemsMap() {
		s := strings.Split(k, ",")
		m = append(m, Metric{
			Description: getHealObjectsFailTotalMD(),
			VariableLabels: map[string]string{
				"mount_path":    s[0],
				"volume_status": s[1],
			},
			Value: float64(v),
		})
	}
	return
}

func getScannedItems(seq *healSequence) (m []Metric) {
	items := seq.getHealedItemsMap()
	m = make([]Metric, 0, len(items))
	for k, v := range items {
		m = append(m, Metric{
			Description:    getHealObjectsHealTotalMD(),
			VariableLabels: map[string]string{"type": string(k)},
			Value:          float64(v),
		})
	}
	return
}

func getObjectsScanned(seq *healSequence) (m []Metric) {
	items := seq.getHealedItemsMap()
	m = make([]Metric, 0, len(items))
	for k, v := range seq.getScannedItemsMap() {
		m = append(m, Metric{
			Description:    getHealObjectsTotalMD(),
			VariableLabels: map[string]string{"type": string(k)},
			Value:          float64(v),
		})
	}
	return
}
func getCacheMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "CacheMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			metrics = make([]Metric, 0, 20)
			cacheObjLayer := newCachedObjectLayerFn()
			// Service not initialized yet
			if cacheObjLayer == nil {
				return
			}
			metrics = append(metrics, Metric{
				Description: getCacheHitsTotalMD(),
				Value:       float64(cacheObjLayer.CacheStats().getHits()),
			})
			metrics = append(metrics, Metric{
				Description: getCacheHitsMissedTotalMD(),
				Value:       float64(cacheObjLayer.CacheStats().getMisses()),
			})
			metrics = append(metrics, Metric{
				Description: getCacheSentBytesMD(),
				Value:       float64(cacheObjLayer.CacheStats().getBytesServed()),
			})
			for _, cdStats := range cacheObjLayer.CacheStats().GetDiskStats() {
				metrics = append(metrics, Metric{
					Description:    getCacheUsagePercentMD(),
					Value:          float64(cdStats.UsagePercent),
					VariableLabels: map[string]string{"disk": cdStats.Dir},
				})
				metrics = append(metrics, Metric{
					Description:    getCacheUsageInfoMD(),
					Value:          float64(cdStats.UsageState),
					VariableLabels: map[string]string{"disk": cdStats.Dir, "level": cdStats.GetUsageLevelString()},
				})
				metrics = append(metrics, Metric{
					Description:    getCacheUsedBytesMD(),
					Value:          float64(cdStats.UsageSize),
					VariableLabels: map[string]string{"disk": cdStats.Dir},
				})
				metrics = append(metrics, Metric{
					Description:    getCacheTotalBytesMD(),
					Value:          float64(cdStats.TotalCapacity),
					VariableLabels: map[string]string{"disk": cdStats.Dir},
				})
			}
			return
		},
	}
}

func getHTTPMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "httpMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			httpStats := globalHTTPStats.toServerHTTPStats()
			metrics = make([]Metric, 0, 3+
				len(httpStats.CurrentS3Requests.APIStats)+
				len(httpStats.TotalS3Requests.APIStats)+
				len(httpStats.TotalS3Errors.APIStats))
			metrics = append(metrics, Metric{
				Description: getS3RejectedAuthRequestsTotalMD(),
				Value:       float64(httpStats.TotalS3RejectedAuth),
			})
			metrics = append(metrics, Metric{
				Description: getS3RejectedTimestampRequestsTotalMD(),
				Value:       float64(httpStats.TotalS3RejectedTime),
			})
			metrics = append(metrics, Metric{
				Description: getS3RejectedHeaderRequestsTotalMD(),
				Value:       float64(httpStats.TotalS3RejectedHeader),
			})
			metrics = append(metrics, Metric{
				Description: getS3RejectedInvalidRequestsTotalMD(),
				Value:       float64(httpStats.TotalS3RejectedInvalid),
			})
			metrics = append(metrics, Metric{
				Description: getS3RequestsInQueueMD(),
				Value:       float64(httpStats.S3RequestsInQueue),
			})
			for api, value := range httpStats.CurrentS3Requests.APIStats {
				metrics = append(metrics, Metric{
					Description:    getS3RequestsInFlightMD(),
					Value:          float64(value),
					VariableLabels: map[string]string{"api": api},
				})
			}
			for api, value := range httpStats.TotalS3Requests.APIStats {
				metrics = append(metrics, Metric{
					Description:    getS3RequestsTotalMD(),
					Value:          float64(value),
					VariableLabels: map[string]string{"api": api},
				})
			}
			for api, value := range httpStats.TotalS3Errors.APIStats {
				metrics = append(metrics, Metric{
					Description:    getS3RequestsErrorsMD(),
					Value:          float64(value),
					VariableLabels: map[string]string{"api": api},
				})
			}
			for api, value := range httpStats.TotalS3Canceled.APIStats {
				metrics = append(metrics, Metric{
					Description:    getS3RequestsCanceledMD(),
					Value:          float64(value),
					VariableLabels: map[string]string{"api": api},
				})
			}
			return
		},
	}
}

func getNetworkMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "networkMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			metrics = make([]Metric, 0, 10)
			metrics = append(metrics, Metric{
				Description: getInternodeFailedRequests(),
				Value:       float64(loadAndResetRPCNetworkErrsCounter()),
			})
			connStats := globalConnStats.toServerConnStats()
			metrics = append(metrics, Metric{
				Description: getInterNodeSentBytesMD(),
				Value:       float64(connStats.TotalOutputBytes),
			})
			metrics = append(metrics, Metric{
				Description: getInterNodeReceivedBytesMD(),
				Value:       float64(connStats.TotalInputBytes),
			})
			metrics = append(metrics, Metric{
				Description: getS3SentBytesMD(),
				Value:       float64(connStats.S3OutputBytes),
			})
			metrics = append(metrics, Metric{
				Description: getS3ReceivedBytesMD(),
				Value:       float64(connStats.S3InputBytes),
			})
			return
		},
	}
}

func getBucketUsageMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "BucketUsageMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			metrics = make([]Metric, 0, 50)
			objLayer := newObjectLayerFn()
			// Service not initialized yet
			if objLayer == nil {
				return
			}

			if globalIsGateway {
				return
			}

			dataUsageInfo, err := loadDataUsageFromBackend(ctx, objLayer)
			if err != nil {
				return
			}

			// data usage has not captured any data yet.
			if dataUsageInfo.LastUpdate.IsZero() {
				return
			}

			metrics = append(metrics, Metric{
				Description: getUsageLastScanActivityMD(),
				Value:       float64(time.Since(dataUsageInfo.LastUpdate)),
			})

			for bucket, usage := range dataUsageInfo.BucketsUsage {
				stat := getLatestReplicationStats(bucket, usage)

				metrics = append(metrics, Metric{
					Description:    getBucketUsageTotalBytesMD(),
					Value:          float64(usage.Size),
					VariableLabels: map[string]string{"bucket": bucket},
				})

				metrics = append(metrics, Metric{
					Description:    getBucketUsageObjectsTotalMD(),
					Value:          float64(usage.ObjectsCount),
					VariableLabels: map[string]string{"bucket": bucket},
				})

				if stat.hasReplicationUsage() {
					metrics = append(metrics, Metric{
						Description:    getBucketRepPendingBytesMD(),
						Value:          float64(stat.PendingSize),
						VariableLabels: map[string]string{"bucket": bucket},
					})
					metrics = append(metrics, Metric{
						Description:    getBucketRepFailedBytesMD(),
						Value:          float64(stat.FailedSize),
						VariableLabels: map[string]string{"bucket": bucket},
					})
					metrics = append(metrics, Metric{
						Description:    getBucketRepSentBytesMD(),
						Value:          float64(stat.ReplicatedSize),
						VariableLabels: map[string]string{"bucket": bucket},
					})
					metrics = append(metrics, Metric{
						Description:    getBucketRepReceivedBytesMD(),
						Value:          float64(stat.ReplicaSize),
						VariableLabels: map[string]string{"bucket": bucket},
					})
					metrics = append(metrics, Metric{
						Description:    getBucketRepPendingOperationsMD(),
						Value:          float64(stat.PendingCount),
						VariableLabels: map[string]string{"bucket": bucket},
					})
					metrics = append(metrics, Metric{
						Description:    getBucketRepFailedOperationsMD(),
						Value:          float64(stat.FailedCount),
						VariableLabels: map[string]string{"bucket": bucket},
					})
				}

				metrics = append(metrics, Metric{
					Description:          getBucketObjectDistributionMD(),
					Histogram:            usage.ObjectSizesHistogram,
					HistogramBucketLabel: "range",
					VariableLabels:       map[string]string{"bucket": bucket},
				})

			}
			return
		},
	}
}
func getLocalStorageMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "localStorageMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			objLayer := newObjectLayerFn()
			// Service not initialized yet
			if objLayer == nil {
				return
			}

			if globalIsGateway {
				return
			}

			metrics = make([]Metric, 0, 50)
			storageInfo, _ := objLayer.LocalStorageInfo(ctx)
			for _, disk := range storageInfo.Disks {
				metrics = append(metrics, Metric{
					Description:    getNodeDiskUsedBytesMD(),
					Value:          float64(disk.UsedSpace),
					VariableLabels: map[string]string{"disk": disk.DrivePath},
				})

				metrics = append(metrics, Metric{
					Description:    getNodeDiskFreeBytesMD(),
					Value:          float64(disk.AvailableSpace),
					VariableLabels: map[string]string{"disk": disk.DrivePath},
				})

				metrics = append(metrics, Metric{
					Description:    getNodeDiskTotalBytesMD(),
					Value:          float64(disk.TotalSpace),
					VariableLabels: map[string]string{"disk": disk.DrivePath},
				})

				metrics = append(metrics, Metric{
					Description:    getClusterDisksFreeInodes(),
					Value:          float64(disk.FreeInodes),
					VariableLabels: map[string]string{"disk": disk.DrivePath},
				})
			}
			return
		},
	}
}
func getClusterStorageMetrics() MetricsGroup {
	return MetricsGroup{
		id:         "ClusterStorageMetrics",
		cachedRead: cachedRead,
		read: func(ctx context.Context) (metrics []Metric) {
			objLayer := newObjectLayerFn()
			// Service not initialized yet
			if objLayer == nil {
				return
			}

			if globalIsGateway {
				return
			}

			// Fetch disk space info, ignore errors
			metrics = make([]Metric, 0, 10)
			storageInfo, _ := objLayer.StorageInfo(ctx)
			onlineDisks, offlineDisks := getOnlineOfflineDisksStats(storageInfo.Disks)
			totalDisks := onlineDisks.Merge(offlineDisks)

			metrics = append(metrics, Metric{
				Description: getClusterCapacityTotalBytesMD(),
				Value:       float64(GetTotalCapacity(storageInfo.Disks)),
			})

			metrics = append(metrics, Metric{
				Description: getClusterCapacityFreeBytesMD(),
				Value:       float64(GetTotalCapacityFree(storageInfo.Disks)),
			})

			metrics = append(metrics, Metric{
				Description: getClusterCapacityUsageBytesMD(),
				Value:       GetTotalUsableCapacity(storageInfo.Disks, storageInfo),
			})

			metrics = append(metrics, Metric{
				Description: getClusterCapacityUsageFreeBytesMD(),
				Value:       GetTotalUsableCapacityFree(storageInfo.Disks, storageInfo),
			})

			metrics = append(metrics, Metric{
				Description: getClusterDisksOfflineTotalMD(),
				Value:       float64(offlineDisks.Sum()),
			})

			metrics = append(metrics, Metric{
				Description: getClusterDisksOnlineTotalMD(),
				Value:       float64(onlineDisks.Sum()),
			})

			metrics = append(metrics, Metric{
				Description: getClusterDisksTotalMD(),
				Value:       float64(totalDisks.Sum()),
			})
			return
		},
	}
}

type minioClusterCollector struct {
	desc *prometheus.Desc
}

func newMinioClusterCollector() *minioClusterCollector {
	return &minioClusterCollector{
		desc: prometheus.NewDesc("minio_stats", "Statistics exposed by MinIO server", nil, nil),
	}
}

// Describe sends the super-set of all possible descriptors of metrics
func (c *minioClusterCollector) Describe(ch chan<- *prometheus.Desc) {
	ch <- c.desc
}

// Collect is called by the Prometheus registry when collecting metrics.
func (c *minioClusterCollector) Collect(out chan<- prometheus.Metric) {

	var wg sync.WaitGroup
	publish := func(in <-chan Metric) {
		defer wg.Done()
		for metric := range in {
			labels, values := getOrderedLabelValueArrays(metric.VariableLabels)
			if metric.Description.Type == histogramMetric {
				if metric.Histogram == nil {
					continue
				}
				for k, v := range metric.Histogram {
					l := append(labels, metric.HistogramBucketLabel)
					lv := append(values, k)
					out <- prometheus.MustNewConstMetric(
						prometheus.NewDesc(
							prometheus.BuildFQName(string(metric.Description.Namespace),
								string(metric.Description.Subsystem),
								string(metric.Description.Name)),
							metric.Description.Help,
							l,
							metric.StaticLabels,
						),
						prometheus.GaugeValue,
						float64(v),
						lv...)
				}
				continue
			}
			metricType := prometheus.GaugeValue
			switch metric.Description.Type {
			case counterMetric:
				metricType = prometheus.CounterValue
			}
			toPost := prometheus.MustNewConstMetric(
				prometheus.NewDesc(
					prometheus.BuildFQName(string(metric.Description.Namespace),
						string(metric.Description.Subsystem),
						string(metric.Description.Name)),
					metric.Description.Help,
					labels,
					metric.StaticLabels,
				),
				metricType,
				metric.Value,
				values...)
			out <- toPost
		}
	}

	// Call peer api to fetch metrics
	peerCh := globalNotificationSys.GetClusterMetrics(GlobalContext)
	selfCh := ReportMetrics(GlobalContext, GetAllGenerators)
	wg.Add(2)
	go publish(peerCh)
	go publish(selfCh)
	wg.Wait()
}

// ReportMetrics reports serialized metrics to the channel passed for the metrics generated.
func ReportMetrics(ctx context.Context, generators func() []MetricsGenerator) <-chan Metric {
	ch := make(chan Metric)
	go func() {
		defer close(ch)
		populateAndPublish(generators, func(m Metric) bool {
			if m.VariableLabels == nil {
				m.VariableLabels = make(map[string]string)
			}
			m.VariableLabels[serverName] = globalLocalNodeName
			for {
				select {
				case ch <- m:
					return true
				case <-ctx.Done():
					return false
				}
			}
		})
	}()
	return ch
}

// minioCollectorV2 is the Custom Collector
type minioCollectorV2 struct {
	generator func() []MetricsGenerator
	desc      *prometheus.Desc
}

// Describe sends the super-set of all possible descriptors of metrics
func (c *minioCollectorV2) Describe(ch chan<- *prometheus.Desc) {
	ch <- c.desc
}

// populateAndPublish populates and then publishes the metrics generated by the generator function.
func populateAndPublish(generatorFn func() []MetricsGenerator, publish func(m Metric) bool) {
	generators := generatorFn()
	for _, g := range generators {
		metricsGroup := g()
		metrics := metricsGroup.cachedRead(GlobalContext, &metricsGroup)
		for _, metric := range metrics {
			if !publish(metric) {
				return
			}
		}
	}
}

// Collect is called by the Prometheus registry when collecting metrics.
func (c *minioCollectorV2) Collect(ch chan<- prometheus.Metric) {

	// Expose MinIO's version information
	minioVersionInfo.WithLabelValues(Version, CommitID).Set(1.0)

	populateAndPublish(c.generator, func(metric Metric) bool {
		labels, values := getOrderedLabelValueArrays(metric.VariableLabels)
		values = append(values, globalLocalNodeName)
		labels = append(labels, serverName)

		if metric.Description.Type == histogramMetric {
			if metric.Histogram == nil {
				return true
			}
			for k, v := range metric.Histogram {
				labels = append(labels, metric.HistogramBucketLabel)
				values = append(values, k)
				ch <- prometheus.MustNewConstMetric(
					prometheus.NewDesc(
						prometheus.BuildFQName(string(metric.Description.Namespace),
							string(metric.Description.Subsystem),
							string(metric.Description.Name)),
						metric.Description.Help,
						labels,
						metric.StaticLabels,
					),
					prometheus.GaugeValue,
					float64(v),
					values...)
			}
			return true
		}

		metricType := prometheus.GaugeValue
		switch metric.Description.Type {
		case counterMetric:
			metricType = prometheus.CounterValue
		}
		ch <- prometheus.MustNewConstMetric(
			prometheus.NewDesc(
				prometheus.BuildFQName(string(metric.Description.Namespace),
					string(metric.Description.Subsystem),
					string(metric.Description.Name)),
				metric.Description.Help,
				labels,
				metric.StaticLabels,
			),
			metricType,
			metric.Value,
			values...)
		return true
	})
}

func getOrderedLabelValueArrays(labelsWithValue map[string]string) (labels, values []string) {
	labels = make([]string, 0)
	values = make([]string, 0)
	for l, v := range labelsWithValue {
		labels = append(labels, l)
		values = append(values, v)
	}
	return
}

// newMinioCollectorV2 describes the collector
// and returns reference of minioCollector for version 2
// It creates the Prometheus Description which is used
// to define Metric and  help string
func newMinioCollectorV2(generator func() []MetricsGenerator) *minioCollectorV2 {
	return &minioCollectorV2{
		generator: generator,
		desc:      prometheus.NewDesc("minio_stats", "Statistics exposed by MinIO server", nil, nil),
	}
}

func metricsServerHandler() http.Handler {

	registry := prometheus.NewRegistry()

	// Report all other metrics
	err := registry.Register(newMinioClusterCollector())
	if err != nil {
		logger.CriticalIf(GlobalContext, err)
	}
	// DefaultGatherers include golang metrics and process metrics.
	gatherers := prometheus.Gatherers{
		registry,
	}
	// Delegate http serving to Prometheus client library, which will call collector.Collect.
	return promhttp.InstrumentMetricHandler(
		registry,
		promhttp.HandlerFor(gatherers,
			promhttp.HandlerOpts{
				ErrorHandling: promhttp.ContinueOnError,
			}),
	)
}

func metricsNodeHandler() http.Handler {
	registry := prometheus.NewRegistry()

	err := registry.Register(newMinioCollectorV2(GetSingleNodeGenerators))
	if err != nil {
		logger.CriticalIf(GlobalContext, err)
	}
	err = registry.Register(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{
		Namespace:    minioNamespace,
		ReportErrors: true,
	}))
	if err != nil {
		logger.CriticalIf(GlobalContext, err)
	}
	err = registry.Register(prometheus.NewGoCollector())
	if err != nil {
		logger.CriticalIf(GlobalContext, err)
	}
	gatherers := prometheus.Gatherers{
		registry,
	}
	// Delegate http serving to Prometheus client library, which will call collector.Collect.
	return promhttp.InstrumentMetricHandler(
		registry,
		promhttp.HandlerFor(gatherers,
			promhttp.HandlerOpts{
				ErrorHandling: promhttp.ContinueOnError,
			}),
	)
}