emit metric for EC2 describeInstance calls

Signed-off-by: Jyoti Mahapatra <jyotima@amazon.com>

pkg/ec2provider/ec2provider.go

@@ -19,6 +19,7 @@ import (
 	"github.com/sirupsen/logrus"
 	"sigs.k8s.io/aws-iam-authenticator/pkg"
 	"sigs.k8s.io/aws-iam-authenticator/pkg/httputil"
+	"sigs.k8s.io/aws-iam-authenticator/pkg/metrics"
 )
 
 const (
@@ -54,13 +55,15 @@ type ec2Requests struct {
 }
 
 type ec2ProviderImpl struct {
-	ec2                ec2iface.EC2API
-	privateDNSCache    ec2PrivateDNSCache
-	ec2Requests        ec2Requests
-	instanceIdsChannel chan string
+	ec2                  ec2iface.EC2API
+	privateDNSCache      ec2PrivateDNSCache
+	ec2Requests          ec2Requests
+	instanceIdsChannel   chan string
+	authenticatorMetrics metrics.Metrics
 }
 
-func New(roleARN string, qps int, burst int) EC2Provider {
+func New(roleARN string, qps int, burst int, authenticatorMetrics metrics.Metrics
+	}) EC2Provider {
 	dnsCache := ec2PrivateDNSCache{
 		cache: make(map[string]string),
 		lock:  sync.RWMutex{},
@@ -74,6 +77,7 @@ func New(roleARN string, qps int, burst int) EC2Provider {
 		privateDNSCache:    dnsCache,
 		ec2Requests:        ec2Requests,
 		instanceIdsChannel: make(chan string, maxChannelSize),
+		authenticatorMetrics: authenticatorMetrics,
 	}
 }
 
@@ -193,6 +197,7 @@ func (p *ec2ProviderImpl) GetPrivateDNSName(id string) (string, error) {
 	}
 
 	logrus.Infof("Calling ec2:DescribeInstances for the InstanceId = %s ", id)
+	p.authenticatorMetrics.EC2DescribeInstanceCallCount.Inc()
 	// Look up instance from EC2 API
 	output, err := p.ec2.DescribeInstances(&ec2.DescribeInstancesInput{
 		InstanceIds: aws.StringSlice([]string{id}),
@@ -254,6 +259,7 @@ func (p *ec2ProviderImpl) StartEc2DescribeBatchProcessing() {
 func (p *ec2ProviderImpl) getPrivateDnsAndPublishToCache(instanceIdList []string) {
 	// Look up instance from EC2 API
 	logrus.Infof("Making Batch Query to DescribeInstances for %v instances ", len(instanceIdList))
+	p.authenticatorMetrics.EC2DescribeInstanceCallCount.Inc()
 	output, err := p.ec2.DescribeInstances(&ec2.DescribeInstancesInput{
 		InstanceIds: aws.StringSlice(instanceIdList),
 	})

pkg/metrics/metrics.go

@@ -26,8 +26,9 @@ func Get() Metrics {
 
 // Metrics are handles to the collectors for prometheus for the various metrics we are tracking.
 type Metrics struct {
-	ConfigMapWatchFailures prometheus.Counter
-	Latency                *prometheus.HistogramVec
+	ConfigMapWatchFailures       prometheus.Counter
+	Latency                      *prometheus.HistogramVec
+	EC2DescribeInstanceCallCount prometheus.Counter
 }
 
 func CreateMetrics(reg prometheus.Registerer) Metrics {
@@ -49,5 +50,12 @@ func CreateMetrics(reg prometheus.Registerer) Metrics {
 			},
 			[]string{"result"},
 		),
+		EC2DescribeInstanceCallCount: factory.NewCounter(
+			prometheus.CounterOpts{
+				Namespace: Namespace,
+				Name:      "ec2_describe_instances_call",
+				Help:      "Number of EC2 describe instances calls.",
+			},
+		),
 	}
 }