Use AWS shared credentials config (#48)

* Always use the shared config in the aws session

* Pass around an instance of an AWS Session

Currently the code creates a new session.Session for every invocation. This
change pulls out that session as a dependency that gets passed into the various
things that invoke it.

lambda/main.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"github.com/aws/aws-lambda-go/lambda"
+	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/buildkite/buildkite-agent-scaler/buildkite"
 	"github.com/buildkite/buildkite-agent-scaler/scaler"
 	"github.com/buildkite/buildkite-agent-scaler/version"
@@ -114,6 +115,9 @@ func Handler(ctx context.Context, evt json.RawMessage) (string, error) {
 		return vi
 	}
 
+	// establish an AWS session to be re-used
+	sess := session.New()
+
 	for {
 		select {
 		case <-timeout:
@@ -124,7 +128,7 @@ func Handler(ctx context.Context, evt json.RawMessage) (string, error) {
 
 			if ssmTokenKey != "" {
 				var err error
-				token, err = scaler.RetrieveFromParameterStore(ssmTokenKey)
+				token, err = scaler.RetrieveFromParameterStore(sess, ssmTokenKey)
 				if err != nil {
 					return "", err
 				}
@@ -170,7 +174,7 @@ func Handler(ctx context.Context, evt json.RawMessage) (string, error) {
 				params.ScaleOutParams.Disable = true
 			}
 
-			scaler, err := scaler.NewScaler(client, params)
+			scaler, err := scaler.NewScaler(client, sess, params)
 			if err != nil {
 				log.Fatal(err)
 			}

main.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"time"
 
+	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/buildkite/buildkite-agent-scaler/buildkite"
 	"github.com/buildkite/buildkite-agent-scaler/scaler"
 )
@@ -23,16 +24,21 @@ func main() {
 		includeWaiting      = flag.Bool("include-waiting", false, "Whether to include jobs behind a wait step for scaling")
 
 		// scale in/out params
-		scaleInFactor   = flag.Float64("scale-in-factor", 1.0, "A factor to apply to scale ins")
-		scaleOutFactor  = flag.Float64("scale-out-factor", 1.0, "A factor to apply to scale outs")
+		scaleInFactor  = flag.Float64("scale-in-factor", 1.0, "A factor to apply to scale ins")
+		scaleOutFactor = flag.Float64("scale-out-factor", 1.0, "A factor to apply to scale outs")
 
 		// general params
 		dryRun = flag.Bool("dry-run", false, "Whether to just show what would be done")
 	)
 	flag.Parse()
 
+	// establish an AWS session to be re-used
+	sess := session.Must(session.NewSessionWithOptions(session.Options{
+		SharedConfigState: session.SharedConfigEnable,
+	}))
+
 	if *ssmTokenKey != "" {
-		token, err := scaler.RetrieveFromParameterStore(*ssmTokenKey)
+		token, err := scaler.RetrieveFromParameterStore(sess, *ssmTokenKey)
 		if err != nil {
 			log.Fatal(err)
 		}
@@ -41,7 +47,7 @@ func main() {
 
 	client := buildkite.NewClient(*buildkiteAgentToken)
 
-	scaler, err := scaler.NewScaler(client, scaler.Params{
+	scaler, err := scaler.NewScaler(client, sess, scaler.Params{
 		BuildkiteQueue:           *buildkiteQueue,
 		AutoScalingGroupName:     *asgName,
 		AgentsPerInstance:        *agentsPerInstance,
@@ -59,7 +65,7 @@ func main() {
 		log.Printf("Running as a dry-run, no changes will be made")
 	}
 
-	var interval time.Duration = 10 * time.Second;
+	var interval time.Duration = 10 * time.Second
 
 	for {
 		minPollDuration, err := scaler.Run()

scaler/asg.go

@@ -19,12 +19,13 @@ type AutoscaleGroupDetails struct {
 
 type asgDriver struct {
 	name string
+	sess *session.Session
 }
 
 func (a *asgDriver) Describe() (AutoscaleGroupDetails, error) {
 	log.Printf("Collecting AutoScaling details for ASG %q", a.name)
 
-	svc := autoscaling.New(session.New())
+	svc := autoscaling.New(a.sess)
 	input := &autoscaling.DescribeAutoScalingGroupsInput{
 		AutoScalingGroupNames: []*string{
 			aws.String(a.name),
@@ -64,7 +65,7 @@ func (a *asgDriver) Describe() (AutoscaleGroupDetails, error) {
 }
 
 func (a *asgDriver) SetDesiredCapacity(count int64) error {
-	svc := autoscaling.New(session.New())
+	svc := autoscaling.New(a.sess)
 	input := &autoscaling.SetDesiredCapacityInput{
 		AutoScalingGroupName: aws.String(a.name),
 		DesiredCapacity:      aws.Int64(count),

scaler/cloudwatch.go

@@ -14,11 +14,12 @@ const (
 
 // cloudWatchMetricsPublisher sends queue metrics to AWS CloudWatch
 type cloudWatchMetricsPublisher struct {
+	sess *session.Session
 }
 
 // Publish queue metrics to CloudWatch Metrics
 func (cp *cloudWatchMetricsPublisher) Publish(orgSlug, queue string, metrics map[string]int64) error {
-	svc := cloudwatch.New(session.New())
+	svc := cloudwatch.New(cp.sess)
 
 	datum := []*cloudwatch.MetricDatum{}
 

scaler/scaler.go

@@ -5,6 +5,7 @@ import (
 	"math"
 	"time"
 
+	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/buildkite/buildkite-agent-scaler/buildkite"
 )
 
@@ -39,12 +40,12 @@ type Scaler struct {
 	metrics interface {
 		Publish(orgSlug, queue string, metrics map[string]int64) error
 	}
-	scaling ScalingCalculator
+	scaling        ScalingCalculator
 	scaleInParams  ScaleParams
 	scaleOutParams ScaleParams
 }
 
-func NewScaler(client *buildkite.Client, params Params) (*Scaler, error) {
+func NewScaler(client *buildkite.Client, sess *session.Session, params Params) (*Scaler, error) {
 	scaler := &Scaler{
 		bk: &buildkiteDriver{
 			client: client,
@@ -68,6 +69,7 @@ func NewScaler(client *buildkite.Client, params Params) (*Scaler, error) {
 	} else {
 		scaler.autoscaling = &asgDriver{
 			name: params.AutoScalingGroupName,
+			sess: sess,
 		}
 
 		if params.PublishCloudWatchMetrics {

scaler/ssm.go

@@ -6,8 +6,8 @@ import (
 	"github.com/aws/aws-sdk-go/service/ssm"
 )
 
-func RetrieveFromParameterStore(key string) (string, error) {
-	ssmClient := ssm.New(session.New())
+func RetrieveFromParameterStore(sess *session.Session, key string) (string, error) {
+	ssmClient := ssm.New(sess)
 	output, err := ssmClient.GetParameter(&ssm.GetParameterInput{
 		Name:           &key,
 		WithDecryption: aws.Bool(true),