Export tier metrics (#18678)

minio_node_tier_ttlb_seconds - Distribution of time to last byte for streaming objects from warm tier
minio_node_tier_requests_success - Number of requests to download object from warm tier that were successful
minio_node_tier_requests_failure - Number of requests to download object from warm tier that failed

cmd/tier_test.go

@@ -0,0 +1,52 @@
+// Copyright (c) 2015-2023 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 (
+	"testing"
+	"time"
+)
+
+func TestTierMetrics(t *testing.T) {
+	tier := "WARM-1"
+	globalTierMetrics.Observe(tier, 200*time.Millisecond)
+	expSuccess := 10
+	expFailure := 5
+	for i := 0; i < expSuccess; i++ {
+		globalTierMetrics.logSuccess(tier)
+	}
+	for i := 0; i < expFailure; i++ {
+		globalTierMetrics.logFailure(tier)
+	}
+	metrics := globalTierMetrics.Report()
+	var succ, fail float64
+	for _, metric := range metrics {
+		switch metric.Description.Name {
+		case tierRequestsSuccess:
+			succ += metric.Value
+		case tierRequestsFailure:
+			fail += metric.Value
+		}
+	}
+	if int(succ) != expSuccess {
+		t.Fatalf("Expected %d successes but got %f", expSuccess, succ)
+	}
+	if int(fail) != expFailure {
+		t.Fatalf("Expected %d failures but got %f", expFailure, fail)
+	}
+}