fix: return GroupArn on placement groups, built from the group name as AWS does

spinifex/handlers/ec2/placementgroup/service_impl.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/ec2"
+	"github.com/mulgadc/spinifex/spinifex/arn"
 	"github.com/mulgadc/spinifex/spinifex/awserrors"
 	"github.com/mulgadc/spinifex/spinifex/config"
 	"github.com/mulgadc/spinifex/spinifex/filterutil"
@@ -49,6 +50,7 @@ type PlacementGroupServiceImpl struct {
 	config   *config.Config
 	natsConn *nats.Conn
 	kv       jetstream.KeyValue
+	region   string
 }
 
 // NewPlacementGroupServiceImplWithNATS creates a placement group service with NATS JetStream.
@@ -66,12 +68,18 @@ func NewPlacementGroupServiceImplWithNATS(ctx context.Context, cfg *config.Confi
 		return nil, fmt.Errorf("migrate %s: %w", KVBucketPlacementGroups, err)
 	}
 
+	region := config.DefaultAWSRegion
+	if cfg != nil && cfg.Region != "" {
+		region = cfg.Region
+	}
+
 	slog.Info("Placement group service initialized with JetStream KV", "bucket", KVBucketPlacementGroups)
 
 	return &PlacementGroupServiceImpl{
 		config:   cfg,
 		natsConn: natsConn,
 		kv:       kv,
+		region:   region,
 	}, nil
 }
 
@@ -568,6 +576,7 @@ func (s *PlacementGroupServiceImpl) FinalizeClusterInstances(ctx context.Context
 // recordToEC2 converts an internal record to the AWS SDK PlacementGroup type.
 func (s *PlacementGroupServiceImpl) recordToEC2(record *PlacementGroupRecord) *ec2.PlacementGroup {
 	pg := &ec2.PlacementGroup{
+		GroupArn:  aws.String(arn.FormatEC2(arn.EC2PlacementGroup, s.region, record.AccountID, record.GroupName)),
 		GroupId:   aws.String(record.GroupId),
 		GroupName: aws.String(record.GroupName),
 		Strategy:  aws.String(record.Strategy),

spinifex/handlers/ec2/placementgroup/service_impl_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/ec2"
 	"github.com/mulgadc/spinifex/spinifex/awserrors"
+	"github.com/mulgadc/spinifex/spinifex/config"
 	"github.com/mulgadc/spinifex/spinifex/kvutil"
 	"github.com/mulgadc/spinifex/spinifex/testutil"
 	"github.com/mulgadc/spinifex/spinifex/utils"
@@ -83,6 +84,34 @@ func TestCreatePlacementGroup_Cluster(t *testing.T) {
 	assert.Nil(t, pg.SpreadLevel)
 }
 
+// AWS builds GroupArn from the group name, not its ID, on create and describe.
+func TestPlacementGroup_GroupArnFromName(t *testing.T) {
+	_, nc, _ := testutil.StartTestJetStream(t)
+	svc, err := NewPlacementGroupServiceImplWithNATS(t.Context(), &config.Config{Region: "ap-southeast-2"}, nc)
+	require.NoError(t, err)
+
+	for _, strategy := range []string{"cluster", "spread"} {
+		name := "arn-" + strategy
+		want := "arn:aws:ec2:ap-southeast-2:123456789012:placement-group/" + name
+
+		pg := createTestGroup(t, svc, name, strategy)
+		assert.Equal(t, want, aws.StringValue(pg.GroupArn))
+
+		out, err := svc.DescribePlacementGroups(context.Background(), &ec2.DescribePlacementGroupsInput{
+			GroupNames: []*string{aws.String(name)},
+		}, testAccountID)
+		require.NoError(t, err)
+		require.Len(t, out.PlacementGroups, 1)
+		assert.Equal(t, want, aws.StringValue(out.PlacementGroups[0].GroupArn))
+	}
+}
+
+func TestPlacementGroup_GroupArnDefaultRegion(t *testing.T) {
+	svc := setupTestService(t)
+	pg := createTestGroup(t, svc, "no-region", "spread")
+	assert.Equal(t, "arn:aws:ec2:us-east-1:123456789012:placement-group/no-region", aws.StringValue(pg.GroupArn))
+}
+
 func TestCreatePlacementGroup_DuplicateName(t *testing.T) {
 	svc := setupTestService(t)
 	createTestGroup(t, svc, "dup-group", "spread")