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Template Format Error in AWS CloudFormation: Resolved

by | Oct 19, 2021

Template Format Error in AWS CloudFormation can come in different forms.

Here, at Bobcares, we assist our customers with several AWS queries as part of our AWS Support Services.

Today, let us see how we can resolve the template errors.

 

Template Format Error in AWS CloudFormation

Moving ahead, our Support Techs discuss different error messages that we may receive. We can select accordingly.

However, to run the AWS Command Line Interface commands, make sure to have the most recent version of the AWS CLI.

  • Validate template syntax

In case of, “JSON not well-formed” or “YAML not well-formed” errors we can use this step.

In order to follow proper JSON or YAML syntax in the CloudFormation template:

  1. Initially, we create the stack with AWS CloudFormation Designer.
  2. Then, we validate the JSON syntax with a text editor or a command-line tool.
  3. After that, we need to validate the YAML syntax with the AWS CloudFormation validate-template command.
  4. Also, validate the JSON or YAML templates with the AWS CloudFormation linter on the GitHub website.
  • Validate logical and physical IDs

For “Unresolved resource dependencies [XXXXXXXX] in the Resources block of the template” errors, we perform this.

1. First, we confirm that resource logical IDs are defined in the template.

2. Also, we need to confirm that resource physical IDs exist in the environment.

For instance, the following JSON and YAML templates do not define the resource ID correctly.

This will eventually return the error.

JSON:

{
"Parameters" : { ... },
"Resources" : {
"EC2Instance01" : {
"Type" : "AWS::EC2::Instance",
"Properties" : {
"ImageId" : {"Ref": "test"},
...
}
}
}
}

YAML:

Parameters:
Resources:
EC2Instance01:
Type: AWS::EC2::Instance
Properties:
ImageId: !Ref: test
  • Validate parameter definitions

For “Unrecognized parameter type: XXXXXXXX” or “Invalid template parameter property ‘XXXXXXXX’” errors, our Support Techs suggest:

1. To set Type to either of the following: String, Number, List<Number>, or CommaDelimitedList.

2. Then in the CloudFormation template, we verify that the parameters include only the following permitted properties:

"Parameters" : {
"ParameterName" : {
"AllowedPattern" : "A regular expression that represents the patterns to allow for String types.",
"AllowedValues" : "An array containing the list of values allowed for the parameter",
"ConstraintDescription" : "A string that explains a constraint when the constraint is violated"
"Default" : "A value of the appropriate type for the template to use if no value is specified when a stack is created. If you define constraints for the parameter, you must specify a value that adheres to those constraints",
"Description" : "A string of up to 4000 characters that describes the parameter",
"MaxLength" : "An integer value that determines the largest number of characters you want to allow for String types",
"MaxValue" : "A numeric value that determines the largest numeric value you want to allow for Number types.",
"MinLength" : "An integer value that determines the smallest number of characters you want to allow for String types.",
"MinValue" : "A numeric value that determines the smallest numeric value you want to allow for Number types.",
"NoEcho" : "Whether to mask the parameter value when a call is made that describes the stack.
If you set the value to true, the parameter value is masked with asterisks (*****).",
"Type" : "The data type for the parameter (DataType)."
},

3. In addition, we confirm that the Parameters section doesn’t contain any intrinsic functions.

For example, here, the default value for ParameterC has the intrinsic function, Fn::Sub. This will eventually lead us to the error.

JSON:

{
"Parameters": {
"ParameterA": {
"Type": "String",
"Default": "abc"
},
"ParameterB": {
"Type": "String",
"Default": "def"
},
"ParameterC": {
"Type": "String",
"Default": {
"Fn::Sub": "${ParameterA}-${ParameterB}"
}
}
},
"Resources": {
"MyS3Bucket": {
"Type": "AWS::S3::Bucket",
"Properties": {
"BucketName": {
"Ref": "ParameterC"
}
}
}
}
}

YAML:

Parameters:
ParameterA:
Type: String
Default: abc
ParameterB:
Type: String
Default: def
ParameterC:
Type: String
Default: !Sub '${ParameterA}-${ParameterB}'
Resources:
MyS3Bucket:
Type: 'AWS::S3::Bucket'
Properties:
BucketName: !Ref ParameterC
  • Confirm that Conditions is specified as a string

Another possible error is “Every Condition member must be a string”.

To resolve this, in the CloudFormation template, we specify Conditions as a string.

For example, in the below example, the condition in the resource EC2RouteA specifies as a list of strings instead of a single string.

These templates result in a validation error.

JSON:

{
"Conditions": {
"ConditionA": {
"Fn::Not": [
{
"Fn::Equals": [
"",
"Sample"
]
}
]
},
"ConditionB": {
"Fn::Not": [
{
"Fn::Equals": [
"",
"Sample"
]
}
]
}
},
"Resources": {
"EC2RouteA": {
"Type": "AWS::EC2::Route",
"Condition": [
"ConditionA",
"ConditionB"
],
"Properties": {
...
}
}
}
}

YAML:

Conditions:
ConditionA: !Not 
- !Equals 
- ''
- Sample
ConditionB: !Not 
- !Equals 
- ''
- Sample
Resources:
EC2RouteA:
Type: 'AWS::EC2::Route'
Condition:
- ConditionA
- ConditionB
Properties:

To resolve this, we add ConditionAandB to the template. After that, we use ConditionAandB as the condition for the EC2RouteA resource.

For instance, see the following JSON and YAML templates:

JSON:

{
"Conditions": {
"ConditionA": {
"Fn::Not": [
{
"Fn::Equals": [
"",
"Sample"
]
}
]
},
"ConditionB": {
"Fn::Not": [
{
"Fn::Equals": [
"",
"Sample"
]
}
]
},
"ConditionAandB": {
"Fn::And": [
{
"Condition": "ConditionA"
},
{
"Condition": "ConditionB"
}
]
}
},
"Resources": {
"EC2RouteA": {
"Type": "AWS::EC2::Route",
"Condition": "ConditionAandB",
"Properties": {
...
}
}
}
}

YAML:

Conditions:
ConditionA:
Fn::Not:
- Fn::Equals:
- ''
- Sample
ConditionB:
Fn::Not:
- Fn::Equals:
- ''
- Sample
ConditionAandB:
Fn::And:
- Condition: ConditionA
- Condition: ConditionB
Resources:
EC2RouteA:
Type: AWS::EC2::Route
Condition: ConditionAandB
Properties:
  • Verify the availability of the resource type

For “Unrecognized resource types: [XXXXXXXX]” errors our Support Techs recommend these steps.

1. Initially, we verify that the resource is available in the AWS Region.

For example, the resource type AWS::WAFRegional::IPSet in the following examples is currently unavailable in ap-south-1.

This will eventually lead us to the error.

JSON:

{
"IPSetlistA": {
"Type": "AWS::WAFRegional::IPSet",
"Properties": {
"Name": "IPSet for IP addresses that are not allowed",
"IPSetDescriptors": [
{
"Type": "IPV4",
"Value": "x.x.x.x/x"
},
{
"Type": "IPV4",
"Value": "x.x.x.x/x"
}
]
}
}
}

YAML:

IPSetlistA:
Type: 'AWS::WAFRegional::IPSet'
Properties:
Name: IPSet for IP addresses that are not allowed
IPSetDescriptors:
- Type: IPV4
Value: x.x.x.x/x
- Type: IPV4
Value: x.x.x.x/x

2. If the template consists of any serverless resources, then we include a Transform declaration.

For example, see the following:

JSON:

{
"Transform": "AWS::Serverless-2016-10-31",
"Resources": {
"MyServerlessFunctionLogicalID": {
"Type": "AWS::Serverless::Function",
"Properties": {
"Handler": "index.handler",
"Runtime": "nodejs8.10",
"CodeUri": "s3://testBucket/mySourceCode.zip"
}
}
}
}

YAML:

Transform: AWS::Serverless-2016-10-31
Resources:
MyServerlessFunctionLogicalID:
Type: AWS::Serverless::Function
Properties:
Handler: index.handler
Runtime: nodejs8.10
CodeUri: 's3://testBucket/mySourceCode.zip'
  • Validate properties, values, and value types

In the case of “Encountered unsupported property XXXXXXXX” errors, we use the valid properties, values, and value types in the template sections and resource definitions.

  • Verify that the resource exists outside the stack

For “The [environmental resource] ‘XXXXXXXX’ does not exist” errors we need to verify that the resource exists outside the stack, or validate dependencies for resources in the same stack

We need to verify the following if we are hardcoding a resource or ARN for a resource that exists outside of the CloudFormation stack into one of the stack’s resources:

  1. Correct resource name or ARN.
  2. The resource exists.
  3. Resource exists in the same AWS Region as the stack.

If the security group doesn’t exist or doesn’t exist in the stack’s AWS Region in your stack that’s specifying a security group, then the AWS::EC2::Instance resource fails with the error.

For example:

LinuxInstance:
Type: AWS::EC2::Instance
Properties:
SubnetId: !Ref ServerSubnetID 
KeyName: !Ref EC2KeyPairName
SecurityGroupIds: sg-1234567890 <This resource must exist and be in the same AWS Region
  • Include a Resources section in the template

For “At least one Resources member must be defined” errors, we must include a Resources section in the CloudFormation template.

Failure of the same will lead us to the error.

  • Verify template properties

For “Invalid template property or properties [XXXXXXXX]” errors our techs recommend the steps below.

We should only use permitted template properties in the CloudFormation template.

In the example here, the bucket resource is on the same level as the Resources section. This returns the error.

This happens because the CloudFormation template validator sees the bucket resource as a section-level specification, which isn’t allowed as a template property.

JSON:

{
"Resources": {
"WaitCondition": {
"Type": "AWS::CloudFormation::WaitCondition"
}
},
"Bucket": {
"Type": "AWS::S3::Bucket",
"Properties": {
"Name": "BucketName"
}
}
}

YAML:

Resources:
WaitCondition:
Type: AWS::CloudFormation::WaitCondition
Bucket:
Type: AWS::S3::Bucket
Properties:
Name: BucketName

[Stuck in between? We are here to assist you any time of the day]

 

Conclusion

In short, we saw how our Support Techs fix the AWS CloudFormation errors for our customers.

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