[INTERNAL] Export numerical kafka_topic_info parameters/labels as individual metrics

Export as numerical metrics:

- topic_info_partitions_count
- topic_info_replication_factor
- topic_info_min_insync_replicas
- topic_info_retention_ms

Partial fix for redpanda-data#116

Author: amuraru

prometheus/collect_topic_info.go

@@ -79,6 +79,38 @@ func (e *Exporter) collectTopicInfo(ctx context.Context, ch chan<- prometheus.Me
 			float64(1),
 			labelsValues...,
 		)
+		ch <- prometheus.MustNewConstMetric(
+			e.topicInfoPartitionsCount,
+			prometheus.GaugeValue,
+			float64(partitionCount),
+			*topic.Topic,
+		)
+		ch <- prometheus.MustNewConstMetric(
+			e.topicInfoReplicationFactor,
+			prometheus.GaugeValue,
+			float64(replicationFactor),
+			*topic.Topic,
+		)
+		if parameter, exists := configsByTopic[*topic.Topic]["min.insync.replicas"]; exists {
+			if value, err := strconv.ParseFloat(parameter, 64); err == nil {
+				ch <- prometheus.MustNewConstMetric(
+					e.topicInfoMinInsyncReplicas,
+					prometheus.GaugeValue,
+					value,
+					*topic.Topic,
+				)
+			}
+		}
+		if parameter, exists := configsByTopic[*topic.Topic]["retention.ms"]; exists {
+			if value, err := strconv.ParseFloat(parameter, 64); err == nil {
+				ch <- prometheus.MustNewConstMetric(
+					e.topicInfoRetentionMs,
+					prometheus.GaugeValue,
+					value,
+					*topic.Topic,
+				)
+			}
+		}
 	}
 	return isOk
 }

prometheus/exporter.go

@@ -32,11 +32,15 @@ type Exporter struct {
 	topicLogDirSize  *prometheus.Desc
 
 	// Topic / Partition
-	topicInfo              *prometheus.Desc
-	topicHighWaterMarkSum  *prometheus.Desc
-	partitionHighWaterMark *prometheus.Desc
-	topicLowWaterMarkSum   *prometheus.Desc
-	partitionLowWaterMark  *prometheus.Desc
+	topicInfo                  *prometheus.Desc
+	topicInfoPartitionsCount   *prometheus.Desc
+	topicInfoReplicationFactor *prometheus.Desc
+	topicInfoMinInsyncReplicas *prometheus.Desc
+	topicInfoRetentionMs       *prometheus.Desc
+	topicHighWaterMarkSum      *prometheus.Desc
+	partitionHighWaterMark     *prometheus.Desc
+	topicLowWaterMarkSum       *prometheus.Desc
+	partitionLowWaterMark      *prometheus.Desc
 
 	// Consumer Groups
 	consumerGroupInfo                    *prometheus.Desc
@@ -114,6 +118,30 @@ func (e *Exporter) InitializeMetrics() {
 		labels,
 		nil,
 	)
+	e.topicInfoPartitionsCount = prometheus.NewDesc(
+		prometheus.BuildFQName(e.cfg.Namespace, "kafka", "topic_info_partitions_count"),
+		"Partitions configuration for a given topic",
+		[]string{"topic_name"},
+		nil,
+	)
+	e.topicInfoReplicationFactor = prometheus.NewDesc(
+		prometheus.BuildFQName(e.cfg.Namespace, "kafka", "topic_info_replication_factor"),
+		"Replication factor configuration for a given topic",
+		[]string{"topic_name"},
+		nil,
+	)
+	e.topicInfoMinInsyncReplicas = prometheus.NewDesc(
+		prometheus.BuildFQName(e.cfg.Namespace, "kafka", "topic_info_min_insync_replicas"),
+		"Min in-sync replicas configuration for a given topic",
+		[]string{"topic_name"},
+		nil,
+	)
+	e.topicInfoRetentionMs = prometheus.NewDesc(
+		prometheus.BuildFQName(e.cfg.Namespace, "kafka", "topic_info_retention_ms"),
+		"Retention time for a given topic",
+		[]string{"topic_name"},
+		nil,
+	)
 	// Partition Low Water Mark
 	e.partitionLowWaterMark = prometheus.NewDesc(
 		prometheus.BuildFQName(e.cfg.Namespace, "kafka", "topic_partition_low_water_mark"),