Return error when cfn template container does not have an image

src/pkg/clouds/aws/ecs/cfn/setup.go

@@ -134,9 +134,14 @@ func (a *AwsEcs) createStackAndWait(ctx context.Context, templateBody string) er
 }
 
 func (a *AwsEcs) SetUp(ctx context.Context, containers []types.Container) error {
-	template, err := createTemplate(a.stackName, containers, TemplateOverrides{VpcID: a.VpcID, Spot: a.Spot}).YAML()
+	tmpl, err := createTemplate(a.stackName, containers, TemplateOverrides{VpcID: a.VpcID, Spot: a.Spot})
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to create CloudFormation template: %w", err)
+	}
+
+	template, err := tmpl.YAML()
+	if err != nil {
+		return fmt.Errorf("failed to marshal CloudFormation template as YAML: %w", err)
 	}
 
 	// Upsert

src/pkg/clouds/aws/ecs/cfn/template.go

@@ -4,6 +4,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"fmt"
 	"math"
 	"os"
 	"strconv"
@@ -58,7 +59,7 @@ type TemplateOverrides struct {
 
 const TemplateRevision = 1 // bump this when the template changes!
 
-func createTemplate(stack string, containers []types.Container, overrides TemplateOverrides) *cloudformation.Template {
+func createTemplate(stack string, containers []types.Container, overrides TemplateOverrides) (*cloudformation.Template, error) {
 	prefix := stack + "-"
 
 	defaultTags := []tags.Tag{
@@ -182,6 +183,9 @@ func createTemplate(stack string, containers []types.Container, overrides Templa
 			// TODO: support pull through cache for other registries
 			// TODO: support private repos (with or without pull-through cache)
 		}
+		if strings.TrimSpace(image) == "" {
+			return nil, fmt.Errorf("container %v is using invalid image: %q", task.Name, task.Image)
+		}
 		images = append(images, image)
 	}
 
@@ -545,5 +549,5 @@ func createTemplate(stack string, containers []types.Container, overrides Templa
 		Value:       cloudformation.Int(TemplateRevision),
 	}
 
-	return template
+	return template, nil
 }