Report on table capacity

Even though we actually set the table capacity in our code, there's
nothing that prevents it from being changed, so it can be useful to
instrument in our code base in case something unexpected happens.

Author: jml

chunk/dynamo_client.go

@@ -2,6 +2,7 @@ package chunk
 
 import (
 	"net/url"
+	"strings"
 	"sync"
 	"time"
 
@@ -18,8 +19,11 @@ const (
 
 type dynamoWatcher struct {
 	accountMaxCapacity *prometheus.GaugeVec
+	tableCapacity      *prometheus.GaugeVec
+
+	dynamoDB  *dynamodb.DynamoDB
+	tableName string
 
-	dynamoDB       *dynamodb.DynamoDB
 	updateInterval time.Duration
 	quit           chan struct{}
 	wait           sync.WaitGroup
@@ -43,15 +47,20 @@ func WatchDynamo(dynamoDBURL string, interval time.Duration) (Watcher, error) {
 	}
 	client := dynamodb.New(session.New(dynamoDBConfig))
 
-	// TODO: Report on table capacity.
-	// tableName := strings.TrimPrefix(dynamoURL.Path, "/")
+	tableName := strings.TrimPrefix(url.Path, "/")
 	w := &dynamoWatcher{
 		accountMaxCapacity: prometheus.NewGaugeVec(prometheus.GaugeOpts{
 			Namespace: "cortex",
 			Name:      "dynamo_account_max_capacity_units",
 			Help:      "Account-wide DynamoDB capacity, measured in DynamoDB capacity units.",
 		}, []string{"op"}),
+		tableCapacity: prometheus.NewGaugeVec(prometheus.GaugeOpts{
+			Namespace: "cortex",
+			Name:      "dynamo_table_capacity_units",
+			Help:      "Per-table DynamoDB capacity, measured in DynamoDB capacity units.",
+		}, []string{"op", "table"}),
 		dynamoDB:       client,
+		tableName:      tableName,
 		updateInterval: interval,
 		quit:           make(chan struct{}),
 	}
@@ -92,12 +101,25 @@ func (w *dynamoWatcher) updateAccountLimits() error {
 	return nil
 }
 
+func (w *dynamoWatcher) updateTableLimits() error {
+	output, err := w.dynamoDB.DescribeTable(&dynamodb.DescribeTableInput{})
+	if err != nil {
+		return err
+	}
+	throughput := output.Table.ProvisionedThroughput
+	w.tableCapacity.WithLabelValues(readLabel, w.tableName).Set(float64(*throughput.ReadCapacityUnits))
+	w.tableCapacity.WithLabelValues(writeLabel, w.tableName).Set(float64(*throughput.WriteCapacityUnits))
+	return nil
+}
+
 // Describe implements prometheus.Collector.
 func (w *dynamoWatcher) Describe(ch chan<- *prometheus.Desc) {
 	w.accountMaxCapacity.Describe(ch)
+	w.tableCapacity.Describe(ch)
 }
 
 // Collect implements prometheus.Collector.
 func (w *dynamoWatcher) Collect(ch chan<- prometheus.Metric) {
 	w.accountMaxCapacity.Collect(ch)
+	w.tableCapacity.Collect(ch)
 }