Merge pull request #5787 from cstyan/reshard-max-logging

Add metrics for max/min/desired shards to queue manager.

documentation/prometheus-mixin/alerts.libsonnet

@@ -211,6 +211,26 @@
               description: 'Prometheus %(prometheusName)s remote write is {{ printf "%%.1f" $value }}s behind for queue {{$labels.queue}}.' % $._config,
             },
           },
+          {
+            alert: 'PrometheusRemoteWriteDesiredShards',
+            expr: |||
+              # Without max_over_time, failed scrapes could create false negatives, see
+              # https://www.robustperception.io/alerting-on-gauges-in-prometheus-2-0 for details.
+              (
+                max_over_time(prometheus_remote_storage_shards_desired{%(prometheusSelector)s}[5m])
+              > on(job, instance) group_right
+                max_over_time(prometheus_remote_storage_shards_max{%(prometheusSelector)s}[5m])
+              )
+            ||| % $._config,
+            'for': '15m',
+            labels: {
+              severity: 'warning',
+            },
+            annotations: {
+              summary: 'Prometheus remote write desired shards calculation wants to run more than configured max shards.',
+              description: 'Prometheus %(prometheusName)s remote write desired shards calculation wants to run {{ printf $value }} shards, which is more than the max of {{ printf `prometheus_remote_storage_shards_max{instance="%%s",%(prometheusSelector)s}` $labels.instance | query | first | value }}.' % $._config,
+            },
+          },
           {
             alert: 'PrometheusRuleFailures',
             expr: |||

storage/remote/queue_manager.go

@@ -143,6 +143,33 @@ var (
 		},
 		[]string{queue},
 	)
+	maxNumShards = promauto.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "shards_max",
+			Help:      "The maximum number of shards that the queue is allowed to run.",
+		},
+		[]string{queue},
+	)
+	minNumShards = promauto.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "shards_min",
+			Help:      "The minimum number of shards that the queue is allowed to run.",
+		},
+		[]string{queue},
+	)
+	desiredNumShards = promauto.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "shards_desired",
+			Help:      "The number of shards that the queues shard calculation wants to run based on the rate of samples in vs. samples out.",
+		},
+		[]string{queue},
+	)
 )
 
 // StorageClient defines an interface for sending a batch of samples to an
@@ -190,6 +217,9 @@ type QueueManager struct {
 	succeededSamplesTotal      prometheus.Counter
 	retriedSamplesTotal        prometheus.Counter
 	shardCapacity              prometheus.Gauge
+	maxNumShards               prometheus.Gauge
+	minNumShards               prometheus.Gauge
+	desiredNumShards           prometheus.Gauge
 }
 
 // NewQueueManager builds a new QueueManager.
@@ -291,10 +321,16 @@ func (t *QueueManager) Start() {
 	t.succeededSamplesTotal = succeededSamplesTotal.WithLabelValues(name)
 	t.retriedSamplesTotal = retriedSamplesTotal.WithLabelValues(name)
 	t.shardCapacity = shardCapacity.WithLabelValues(name)
+	t.maxNumShards = maxNumShards.WithLabelValues(name)
+	t.minNumShards = minNumShards.WithLabelValues(name)
+	t.desiredNumShards = desiredNumShards.WithLabelValues(name)
 
 	// Initialise some metrics.
 	t.shardCapacity.Set(float64(t.cfg.Capacity))
 	t.pendingSamplesMetric.Set(0)
+	t.maxNumShards.Set(float64(t.cfg.MaxShards))
+	t.minNumShards.Set(float64(t.cfg.MinShards))
+	t.desiredNumShards.Set(float64(t.cfg.MinShards))
 
 	t.shards.start(t.numShards)
 	t.watcher.Start()
@@ -334,6 +370,9 @@ func (t *QueueManager) Stop() {
 	succeededSamplesTotal.DeleteLabelValues(name)
 	retriedSamplesTotal.DeleteLabelValues(name)
 	shardCapacity.DeleteLabelValues(name)
+	maxNumShards.DeleteLabelValues(name)
+	minNumShards.DeleteLabelValues(name)
+	desiredNumShards.DeleteLabelValues(name)
 }
 
 // StoreSeries keeps track of which series we know about for lookups when sending samples to remote.
@@ -502,6 +541,7 @@ func (t *QueueManager) calculateDesiredShards() {
 	}
 
 	numShards := int(math.Ceil(desiredShards))
+	t.desiredNumShards.Set(float64(numShards))
 	if numShards > t.cfg.MaxShards {
 		numShards = t.cfg.MaxShards
 	} else if numShards < t.cfg.MinShards {