aws cloudformation deploy doesn't recognize change in default value

Question

When we deploy a new version of a template, the difference in the new "default parameter" is not recognized by aws cloudformation deploy. Example:

```
cat < cfn.yaml 
---
AWSTemplateFormatVersion: "2010-09-09"
Description: an example

Parameters:
  Param:
    Type: String
    Default: '1'

Resources:

SsmParameter:
    Type: AWS::SSM::Parameter
    Properties:
      Name: /example
      Type: String
      Value: !Ref Param
EOF
```
Then use AWS CLI to deploy and check the result:

```
aws cloudformation deploy --template-file cfn.yaml --stack-name update-check
aws ssm get-parameter --name /example |  | jq '.Parameter.Value'
```
This gives "1" as a result

Now, change the CloudFormation template file:

```
cat < cfn.yaml 
---
AWSTemplateFormatVersion: "2010-09-09"
Description: an example

Parameters:
  Param:
    Type: String
    Default: **'2'**

Resources:

SsmParameter:
    Type: AWS::SSM::Parameter
    Properties:
      Name: /example
      Type: String
      Value: !Ref Param
EOF
```
Try to re-deploy this template:
```
aws cloudformation deploy --template-file cfn.yaml --stack-name update-check
```
Output:
```

Waiting for changeset to be created..

No changes to deploy. Stack update-check is up to date
```

This seems a bug to us, can you fix this?

Answer

Hi THere

Use [update-stack](https://awscli.amazonaws.com/v2/documentation/api/2.1.21/reference/cloudformation/update-stack.html)

example

```
cat < cfn.yaml 
---
AWSTemplateFormatVersion: "2010-09-09"
Description: an example

Parameters:
  Param:
    Type: String
    Default: '1'

Resources:

SsmParameter:
    Type: AWS::SSM::Parameter
    Properties:
      Name: /example
      Type: String
      Value: !Ref Param
EOF
```

```
aws cloudformation deploy --template-file cfn.yaml --stack-name update-check
aws ssm get-parameter --name /example | jq '.Parameter.Value'
"1"
```
Now change the template

```
cat < cfn.yaml 
---
AWSTemplateFormatVersion: "2010-09-09"
Description: an example

Parameters:
  Param:
    Type: String
    Default: '2'

Resources:

SsmParameter:
    Type: AWS::SSM::Parameter
    Properties:
      Name: /example
      Type: String
      Value: !Ref Param
EOF
```

Update the stack

```
[cloudshell-user@ ~]$ aws cloudformation update-stack --template-body file://cfn.yaml --stack-name update-check

{
    "StackId": "arn:aws:cloudformation:us-east-1:#########:stack/update-check/52e8a4f0-303d-11ed-8d03-xxxxxxxxxx"
}

[cloudshell-user@ ~]$ aws ssm get-parameter --name /example | jq '.Parameter.Value'
"2"
```

Answer

I also tried it, and indeed reproduced the same issue.

This may be similar to the following GitHub Issue. [1].

[1] SSM Dynamic Reference Change not detected - Issue #844 - aws-cloudformation/cloudformation-coverage-roadmap
https://github.com/aws-cloudformation/cloudformation-coverage-roadmap/issues/844

The above Issue is open, so reporting this event may be considered for a fix.

aws cloudformation deploy doesn't recognize change in default value

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