Don't use indented json, since it's big.

scheduler/cloudformation/cloudformation.go

@@ -29,6 +29,13 @@ import (
 // The identifier of the ECS Service resource in CloudFormation.
 const ecsServiceType = "AWS::ECS::Service"
 
+// CloudFormation limits
+//
+// See http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cloudformation-limits.html
+const (
+	MaxTemplateSize = 460800 // bytes
+)
+
 // DefaultStackNameTemplate is the default text/template for generating a
 // CloudFormation stack name for an app.
 var DefaultStackNameTemplate = template.Must(template.New("stack_name").Parse("{{.Name}}"))
@@ -84,7 +91,7 @@ type serviceMetadata struct {
 type Scheduler struct {
 	// Template is a text/template that will be executed using the
 	// twelvefactor.Manifest as data. This template should return a valid
-	// CloudFormation JSON manifest.
+	// CloudFormation JSON template.
 	Template Template
 
 	// The ECS cluster to run tasks in.

scheduler/cloudformation/template.go

@@ -1,7 +1,6 @@
 package cloudformation
 
 import (
-	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -102,13 +101,7 @@ func (t *EmpireTemplate) Execute(w io.Writer, data interface{}) error {
 		return err
 	}
 
-	raw, err := json.MarshalIndent(v, "", "  ")
-	if err != nil {
-		return err
-	}
-
-	_, err = io.Copy(w, bytes.NewReader(raw))
-	return err
+	return json.NewEncoder(w).Encode(v)
 }
 
 // Build builds a Go representation of a CloudFormation template for the app.

scheduler/cloudformation/template_test.go

@@ -76,19 +76,7 @@ func TestEmpireTemplate(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		tmpl := &EmpireTemplate{
-			Cluster:                 "cluster",
-			ServiceRole:             "ecsServiceRole",
-			InternalSecurityGroupID: "sg-e7387381",
-			ExternalSecurityGroupID: "sg-1938737f",
-			InternalSubnetIDs:       []string{"subnet-bb01c4cd", "subnet-c85f4091"},
-			ExternalSubnetIDs:       []string{"subnet-ca96f4cd", "subnet-a13b909c"},
-			CustomResourcesTopic:    "sns topic arn",
-			HostedZone: &route53.HostedZone{
-				Id:   aws.String("Z3DG6IL3SJCGPX"),
-				Name: aws.String("empire"),
-			},
-		}
+		tmpl := newTemplate()
 		buf := new(bytes.Buffer)
 
 		filename := fmt.Sprintf("templates/%s", tt.file)
@@ -102,3 +90,49 @@ func TestEmpireTemplate(t *testing.T) {
 		ioutil.WriteFile(filename, buf.Bytes(), 0660)
 	}
 }
+
+func TestEmpireTemplate_Large(t *testing.T) {
+	labels := make(map[string]string)
+	env := make(map[string]string)
+	for i := 0; i < 100; i++ {
+		env[fmt.Sprintf("ENV_VAR_%d", i)] = fmt.Sprintf("value%d", i)
+	}
+	app := &scheduler.App{
+		ID:   "",
+		Name: "bigappwithlotsofprocesses",
+	}
+
+	for i := 0; i < 60; i++ {
+		app.Processes = append(app.Processes, &scheduler.Process{
+			Type:    fmt.Sprintf("%d", i),
+			Command: []string{"./bin/web"},
+			Env:     env,
+			Labels:  labels,
+		})
+	}
+
+	tmpl := newTemplate()
+	buf := new(bytes.Buffer)
+
+	err := tmpl.Execute(buf, app)
+	assert.NoError(t, err)
+	assert.Condition(t, func() bool {
+		return buf.Len() < MaxTemplateSize
+	}, fmt.Sprintf("template must be smaller than %d, was %d", MaxTemplateSize, buf.Len()))
+}
+
+func newTemplate() *EmpireTemplate {
+	return &EmpireTemplate{
+		Cluster:                 "cluster",
+		ServiceRole:             "ecsServiceRole",
+		InternalSecurityGroupID: "sg-e7387381",
+		ExternalSecurityGroupID: "sg-1938737f",
+		InternalSubnetIDs:       []string{"subnet-bb01c4cd", "subnet-c85f4091"},
+		ExternalSubnetIDs:       []string{"subnet-ca96f4cd", "subnet-a13b909c"},
+		CustomResourcesTopic:    "sns topic arn",
+		HostedZone: &route53.HostedZone{
+			Id:   aws.String("Z3DG6IL3SJCGPX"),
+			Name: aws.String("empire"),
+		},
+	}
+}