为 CloudFormation 传递参数文件不适用于 YML

Question

Solution : Don't use yml.

I'm trying to pass parameters that hold the db name and the db password along with my aws cloudformation stack-create command. I get back an error that doesn't make a whole lot of sense.

Value of property MasterUsername must be of type String

Now, one thing to know is that I have console access so I can literally see the password and username come back in the console as what was set. They both look like strings to me.

YAML Version

I'm defining the stack in a template like this:

Parameters:
  DBUser:
    Description: db user
    Type: String
    MinLength: '4'
    MaxLength: '16'
    AllowedPattern: '[a-zA-Z][a-zA-Z0-9]*'
    ConstraintDescription: some description
  DBPass:
    Description: db password
    Type: String
    MinLength: '8'
    MaxLength: '36'
    AllowedPattern: '[a-zA-Z0-9]*'
    ConstraintDescription: must contain only alphanumeric characters
Resources:
  AppNode:
   (...)
  DatabaseInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      DBName: app
      DBInstanceClass: db.t2.micro
      Engine: postgres
      EngineVersion: 10
      MasterUsername:
        - !Ref DBUser
      MasterUserPassword:
        - !Ref DBPass
  DatabaseSG:
    Type: AWS::RDS::DBSecurityGroup
    Properties:
      GroupDescription: Security Group for RDS public access
      DBSecurityGroupIngress:
        - CIDRIP: 0.0.0.0/0

Inside of my .env file I have this:

[
  {
    "ParameterKey": "DBUser",
    "ParameterValue": "root"
  },
  {
    "ParameterKey": "DBPass",
    "ParameterValue": "mydbpassword"
  }
]

I run this command:

aws cloudformation create-stack --stack-name app --template-body file://$PWD/stack.json --region us-west-2 --parameters file://$PWD/.env.json

for the file type.

So the first thing that comes to mind is that maybe it's getting those values as blank. That can't be the case though because if I don't pass a template or parameters at all it, throws a different error.

An error occurred (ValidationError) when calling the CreateStack operation: Parameters: [DBUser, DBPass] must have values

Did AWS redefine what a string is or what is going on here?

Answer 1

Correct your template as below.

Resources:
  AppNode:
   (...)
  DatabaseInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      DBName: app
      DBInstanceClass: db.t2.micro
      Engine: postgres
      EngineVersion: 10
      MasterUsername:
        !Ref DBUser
      MasterUserPassword:
        !Ref DBPass

When you use - !Ref DBUser , it signifies a LIST in yaml, not String . MasterUserPassword and MasterUserPassword are both of type String . AWS supports both .yml and .yaml extensions. So there is no issue with you extensions.

Answer 2

Sorry to say that external parameters are not supported via file for yaml files.

You can pass them in command line as a workaround.

Reference:

https://github.com/aws/aws-cli/issues/2275

There is still in work in progress.

Hope it helps.

EDIT1:

      MasterUsername:
        - ${DBUser}
      MasterUserPassword:
        - ${DBPass}

Looks like your YAML syntax is not correct.

Reference:

http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/quickref-general.html

Answer 3

MasterUsername must be of type String

Here you have a list (array), not string:

MasterUsername:
        - !Ref DBUser

Use on the same line instead:

MasterUsername: !Ref DBUser