Merge pull request #17 from codesuki/detect-cluster

Automatically detect region

Author: codesuki

Diff for: Makefile

@@ -16,7 +16,7 @@ docker:
 build: deps
 	for GOOS in darwin linux; do \
 		for GOARCH in 386 amd64; do \
-			go build -ldflags "$(LDFLAGS)" -v -o build/$(NAME)-$$GOOS-$$GOARCH ; \
+			GOOS=$$GOOS GOARCH=$$GOARCH go build -ldflags "$(LDFLAGS)" -v -o build/$(NAME)-$$GOOS-$$GOARCH ; \
 		done \
 	done
 

Diff for: ec2.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/ec2metadata"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/ec2"
 )
@@ -11,7 +12,9 @@ type ec2Client struct {
 }
 
 func newEC2(region string, sess *session.Session) *ec2Client {
-	return &ec2Client{ec2.New(sess, aws.NewConfig().WithRegion(region))}
+	return &ec2Client{
+		ec2: ec2.New(sess, aws.NewConfig().WithRegion(region)),
+	}
 }
 
 func (e *ec2Client) describeInstance(id *string) (*ec2.Instance, error) {
@@ -26,3 +29,15 @@ func (e *ec2Client) describeInstance(id *string) (*ec2.Instance, error) {
 	}
 	return resp.Reservations[0].Instances[0], nil
 }
+
+type ec2Meta struct {
+	metadata *ec2metadata.EC2Metadata
+}
+
+func NewEC2Metadata(sess *session.Session) *ec2Meta {
+	return &ec2Meta{metadata: ec2metadata.New(sess)}
+}
+
+func (m *ec2Meta) region() (string, error) {
+	return m.metadata.Region()
+}

Diff for: main.go

@@ -37,7 +37,7 @@ var (
 var (
 	app = kingpin.New("ecs-gen", "docker-gen for AWS ECS.")
 
-	region       = app.Flag("region", "AWS region.").Short('r').Default("ap-northeast-1").String()
+	region       = app.Flag("region", "AWS region.").Short('r').String()
 	cluster      = app.Flag("cluster", "ECS cluster name.").Short('c').String()
 	templateFile = app.Flag("template", "Path to template file.").Short('t').Required().ExistingFile()
 	outputFile   = app.Flag("output", "Path to output file.").Short('o').Required().String()
@@ -56,21 +56,14 @@ func main() {
 	app.Version(version)
 	app.DefaultEnvars()
 	kingpin.MustParse(app.Parse(os.Args[1:]))
-	if *hostVar == "" {
-		log.Fatalf("host-var must not be empty")
-	}
-	if *cluster == "" {
-		var err error
-		cluster, err = findClusterName()
-		if err != nil || *cluster == "" {
-			log.Fatalf("could not determine cluster name. please define using --cluster / -c")
-		}
-		log.Println("found cluster name to be:", *cluster)
-	}
 	sess, err := session.NewSession()
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
+	meta := NewEC2Metadata(sess)
+	checkRegionFlag(meta)
+	checkHostVarFlag()
+	checkClusterFlag()
 	ec2 := newEC2(*region, sess)
 	ecs := newECS(*region, sess)
 	if *once {
@@ -83,6 +76,34 @@ func main() {
 	}
 }
 
+func checkHostVarFlag() {
+	if *hostVar == "" {
+		log.Fatalf("host-var must not be empty")
+	}
+}
+
+func checkClusterFlag() {
+	if *cluster == "" {
+		var err error
+		cluster, err = findClusterName()
+		if err != nil || *cluster == "" {
+			log.Fatalf("could not determine cluster name. please define using --cluster / -c")
+		}
+		log.Println("found cluster name to be:", *cluster)
+	}
+}
+
+func checkRegionFlag(meta *ec2Meta) {
+	if *region == "" {
+		r, err := meta.region()
+		if err != nil {
+			log.Fatalf("could not determine cluster region. please define using --region / -r")
+		}
+		*region = r
+		log.Println("found cluster region to be:", *region)
+	}
+}
+
 func execute(ec2 *ec2Client, ecs *ecsClient) {
 	updateAndWrite(ec2, ecs)
 	var err error