feat: Add Metrics V3 API (#19068)

Metrics v3 is mainly a reorganization of metrics into smaller groups of
metrics and the removal of internal aggregation of metrics received from
peer nodes in a MinIO cluster.

This change adds the endpoint `/minio/metrics/v3` as the top-level metrics
endpoint and under this, various sub-endpoints are implemented. These
are currently documented in `docs/metrics/v3.md`

The handler will serve metrics at any path
`/minio/metrics/v3/PATH`, as follows:

when PATH is a sub-endpoint listed above => serves the group of
metrics under that path; or when PATH is a (non-empty) parent 
directory of the sub-endpoints listed above => serves metrics
from each child sub-endpoint of PATH. otherwise, returns a no 
resource found error

All available metrics are listed in the `docs/metrics/v3.md`. More will
be added subsequently.

cmd/metrics-v3-cluster-erasure-set.go

@@ -0,0 +1,89 @@
+// Copyright (c) 2015-2024 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"
+	"strconv"
+)
+
+const (
+	erasureSetOverallWriteQuorum = "overall_write_quorum"
+	erasureSetOverallHealth      = "overall_health"
+	erasureSetReadQuorum         = "read_quorum"
+	erasureSetWriteQuorum        = "write_quorum"
+	erasureSetOnlineDrivesCount  = "online_drives_count"
+	erasureSetHealingDrivesCount = "healing_drives_count"
+	erasureSetHealth             = "health"
+)
+
+const (
+	poolIDL = "pool_id"
+	setIDL  = "set_id"
+)
+
+var (
+	erasureSetOverallWriteQuorumMD = NewGaugeMD(erasureSetOverallWriteQuorum,
+		"Overall write quorum across pools and sets")
+	erasureSetOverallHealthMD = NewGaugeMD(erasureSetOverallHealth,
+		"Overall health across pools and sets (1=healthy, 0=unhealthy)")
+	erasureSetReadQuorumMD = NewGaugeMD(erasureSetReadQuorum,
+		"Read quorum for the erasure set in a pool", poolIDL, setIDL)
+	erasureSetWriteQuorumMD = NewGaugeMD(erasureSetWriteQuorum,
+		"Write quorum for the erasure set in a pool", poolIDL, setIDL)
+	erasureSetOnlineDrivesCountMD = NewGaugeMD(erasureSetOnlineDrivesCount,
+		"Count of online drives in the erasure set in a pool", poolIDL, setIDL)
+	erasureSetHealingDrivesCountMD = NewGaugeMD(erasureSetHealingDrivesCount,
+		"Count of healing drives in the erasure set in a pool", poolIDL, setIDL)
+	erasureSetHealthMD = NewGaugeMD(erasureSetHealth,
+		"Health of the erasure set in a pool (1=healthy, 0=unhealthy)",
+		poolIDL, setIDL)
+)
+
+func b2f(v bool) float64 {
+	if v {
+		return 1
+	}
+	return 0
+}
+
+// loadClusterErasureSetMetrics - `MetricsLoaderFn` for cluster storage erasure
+// set metrics.
+func loadClusterErasureSetMetrics(ctx context.Context, m MetricValues, c *metricsCache) error {
+	result, _ := c.esetHealthResult.Get()
+
+	m.Set(erasureSetOverallWriteQuorum, float64(result.WriteQuorum))
+	m.Set(erasureSetOverallHealth, b2f(result.Healthy))
+
+	for _, h := range result.ESHealth {
+		poolLV := strconv.Itoa(h.PoolID)
+		setLV := strconv.Itoa(h.SetID)
+		m.Set(erasureSetReadQuorum, float64(h.ReadQuorum),
+			poolIDL, poolLV, setIDL, setLV)
+		m.Set(erasureSetWriteQuorum, float64(h.WriteQuorum),
+			poolIDL, poolLV, setIDL, setLV)
+		m.Set(erasureSetOnlineDrivesCount, float64(h.HealthyDrives),
+			poolIDL, poolLV, setIDL, setLV)
+		m.Set(erasureSetHealingDrivesCount, float64(h.HealingDrives),
+			poolIDL, poolLV, setIDL, setLV)
+		m.Set(erasureSetHealth, b2f(h.Healthy),
+			poolIDL, poolLV, setIDL, setLV)
+	}
+
+	return nil
+}