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CloudFormation Parameters: Make your life simple

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CloudFormation Parameters pass input values to the CloudFormation template when you create or update a stack of AWS resources. 

That definition is like watching a movie from the second half! So, lets rewind and start with a fundamental question. 

What is AWS CloudFormation ?

AWS CloudFormation is an Infrastructure as Code service by Amazon to model, provision and configure AWS resources in the Cloud. You do this by creating a template, which is a simple text file in JSON or YAML format. 

In case you are not familiar with JSON and YAML, JSON stands for JavaScript Object Notation and is lightweight data-interchange format easy for humans and machines to comprehend. Similarly, YAML (“YAML Aint Markup Language”) is a data-serialization language and uses indentation for formatting. This minimal syntax makes it easy to understand and write.

Let’s walk thru an example to make better sense.

Assume you want to create a DynamoDB table with indexes. You would have to manually provision and configure the table name, keys, capacity units, field attributes, primary and secondary indexes and more. With CloudFormation, you specify your required AWS resources and its properties in your template and create a stack from either the CLI, API or Console. Think of it as automating the traditional manual and tedious process.

Now let’s get back to focusing on CloudFormation Parameters and look at their attributes.

  1. AWS Cloudformation basics
  2. Cloudformation Parameters – Properties
  3. Cloudformation Parameters – Types
  4. Cloudformation Parameters Examples

AWS CloudFormation Basics

aws cloudformation

A CloudFormation template is composed of multiple sections – Format Version, Description, Metadata, Parameters, Mappings, Conditions, Transform, Resources and Output. Parameters, though an optional section in the template can be used to turbo charge your resource deployment game.

Like I mentioned earlier, CloudFormation Parameters are used to pass input values to the template during run-time when creating or updating a stack. These parameters are then referenced from the Resources or Output sections in the template. Keep the following points in mind when you use parameters in your CloudFormation template.

  • A parameter can only be referenced in the context of the template it is declared in. In other words, they are not global.
  • You have to provide a value during runtime. If you decide to declare a parameter and not use it, then it has to have a default value assigned.
  • You can have a maximum of 60 parameters in a template and each one must have a unique logical name.
  • And finally, every parameter should have a type assigned to it.

CloudFormation Parameters - Properties

When using CloudFormation Parameters, there are 11 properties you can specify for control and structure. Almost all of them are optional, except for the Type parameter. The table below lists the parameter properties and description.

 Parameter PropertiesWhat it does
1AllowedPatternThe approved format for the string type specified as a regular expression. For a database password for instance, this could be “^[a-zA-Z0-9]*$”
2AllowedValuesList containing the valid values for a parameter
3ConstraintDescriptionDescriptive text on why a constraint was violated
4DefaultFallback value to use if a specific parameter is not specified
5DescriptionA description of what the parameter does limited to 4000 bytes
6MaxLengthLargest value allowed for a String type
7MaxValueLargest value allowed for a Number type
8MinLengthSmallest value allowed for a String type
9MinValueSmallest value allowed for a Number type
10NoEchoUsed to mask the parameter value displayed. As a best practice, try not to use this parameter
11TypeThe datatype of the parameter. Can be String, Number, List, CommaDelimitedList, AWS-Specific Parameter types or SSM Parameter Types


Related: Amazon Athena SQL basics 

CloudFormation Parameters - Types

As mentioned earlier, a CloudFormation template has multiple sections, and CloudFormation Parameters are used to pass input values to the template.

A CloudFormation Parameter Type is the data type for the parameter. There are 6 CloudFormation parameter types and it is a required property of a parameter.

 Parameter TypeWhat it does
1StringLiteral String
2NumberInteger or floating-point number
3List An array of integers such as [“10″,”20”]
4CommaDelimitedListAn array of strings such as [“Name1”, “Name2”]
5AWS-Specific Parameter TypesAWS Specific parameter types
6SSM Parameter TypesParameters from the System Manager Parameter Store

CloudFormation Parameters examples

If all this technical jargon is making your head spin, don’t fret! We will walk through the top 5 frequently used CloudFormation Parameter patterns. Once you get familiar with them, try tweaking them for your specific use cases.

Example 1: Create an AWS-Specific Cloudformation Parameter for an EC2 Key Pair

JSON

"Parameters" : {
    "KeyName": {
      "Description" : "EC2 Key Pair Name",
      "Type": "AWS::EC2::KeyPair::KeyName",
        "ConstraintDescription" : "EC2 Key Pair must exist"
     }
}

YAML

Parameters :
   KeyName:
      Description : EC2 Key Pair Name
      Type: AWS::EC2::KeyPair::KeyName
      ConstraintDescription : EC2 Key Pair must exist

Example 2: Create CloudFormation Parameters for SSH access to an EC2 Instance

JSON

"Parameters" : {
    "SSHLocation" : {
            "Description" : " IP address for SSH to the EC2 instance",
             "Type": "String",
             "MinLength": "9",
             "MaxLength": "18",
             "Default": "0.0.0.0/0",
"AllowedPattern": "(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\
(\\d{1,3})/(\\d{1,2})",
"ConstraintDescription": "IP in x.x.x.x/x format." 
        }
}

YAML

Parameters : 
       SSHLocation :
           Description : IP address for SSH to the EC2 instance
           Type: String
           MinLength: 9
           MaxLength: 18
           Default: 0000/0
           AllowedPattern: (\\d13)\\(\\d13)\\(\\d13)
                            \\(\\d13)/(\\d12)
           ConstraintDescription: IP CIDR range in xxxx/x format

Example 3: Create CloudFormation Parameters for a Database

In this example, we will create 3 parameters for a DynamoDB database. One for the Database Name (DBName),One for the Database User (DBUser) and one for the Database Password (DB Password). 

This example can be used for other databases and any scenario requiring Username and Password parameters.

JSON

"Parameters" : { 
"DBName": {
"Default": "testDynamoDB",
"Description" : "DynamoDB database name",
"Type": "String",
"MinLength": "1",
"MaxLength": "64",
"AllowedPattern" : "[a-zA-Z][a-zA-Z0-9]*",
"ConstraintDescription" : "Must start with a letter and contain only alphanumeric characters"
};
"DBUser": {
"NoEcho": "true",
"Description" : "Username for DynamoDB database",
"Type": "String",
"MinLength": "1",
"MaxLength": "16",
"AllowedPattern" : "[a-zA-Z][a-zA-Z0-9]*",
"ConstraintDescription" : "Must start with a letter and contain only alphanumeric characters"
},
"DBPassword": {
"NoEcho": "true",
"Description" : "Password for DynamoDB database",
"Type": "String",
"MinLength": "8",
"MaxLength": "41",
"AllowedPattern" : "[a-zA-Z0-9]*",
"ConstraintDescription" : "Alphanumeric characters only"
}
}

YAML

Parameters :
DBName:
Default: testDynamoDB
Description : DynamoDB database name
Type: String
MinLength: 1
MaxLength: 64
AllowedPattern : [a-zA-Z][a-zA-Z0-9]*
ConstraintDescription : Must start with a letter and contain only alphanumeric characters
DBUser:
NoEcho: true
Description : Username for DynamoDB database
Type: String
MinLength: 1
MaxLength: 16
AllowedPattern : [a-zA-Z][a-zA-Z0-9]*
ConstraintDescription : Must start with a letter and contain only alphanumeric characters
DBPassword:
NoEcho: true
Description : Password for DynamoDB database
Type: String
MinLength: 8
MaxLength: 41
AllowedPattern : [a-zA-Z0-9]*
ConstraintDescription : Alphanumeric characters only

Example 4: Create CloudFormation Parameters for an Email Address

JSON

"Parameters": { 
     "EMailAddress": {
         "Description": "Email address for issue notification",
         "Type": "String",
       "AllowedPattern": "([a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|
(([a-zA-Z0-9\\-]+\\.)+)) ([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?)",
         "ConstraintDescription": "Enter a valid email address."
     }
}

YAML

Parameters: 
     EMailAddress:
         Description: Email address for issue notification
         Type: String
       AllowedPattern: [a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([a-zA-Z0-9\\-]+\\.)+))
([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?
ConstraintDescription: Enter a valid email address

Example 5: Create CloudFormation Parameters for a SageMaker EC2 Instance Type

JSON

"Parameters" : {
     "InstanceType" : {
         "Description" : "SageMaker EC2 instance type",
         "Type" : "String",
         "Default" : "ml.m4.xlarge",
 "AllowedValues" : [ "ml.m4.xlarge",
"ml.m4.4xlarge",
"ml.m4.10xlarge",
"ml.c4.xlarge",
"ml.c4.2xlarge",
"ml.c4.8xlarge",
"ml.p2.xlarge",
"ml.p2.8xlarge",
"ml.p2.16xlarge"],        
"ConstraintDescription" : "Must be a valid EC2 instance type." 
         }
}

YAML

Parameters : 
     InstanceType :
         Description : SageMaker EC2 instance type
         Type : String
         Default : ml.m4.xlarge
         AllowedValues :
                 - ml.m4.xlarge
                 - ml.m4.4xlarge
                 - ml.m4.10xlarge
                 - ml.c4.xlarge
                 - ml.c4.2xlarge
                 - ml.c4.8xlarge
                 - ml.p2.xlarge
                 - ml.p2.8xlarge
                 - ml.p2.16xlarge
       ConstraintDescription : Must be a valid EC2 instance type

In Conclusion

Keep the following key points in mind: 

  • CloudFormation Parameters are an optional section in the template. However, using them will make your template flexible and dynamic.
  • At a minimum, you need to specify a logical id (name) and type for your parameter.
  • For AWS specific values, always use the AWS-Specific Parameter Types.
  • Though not required, using Parameter Constraints and Defaults is considered best practice.

Now that we covered some of the basics. See if you can provision an Amazon Redshift Cluster using AWS CloudFormation. Here are a few articles to get you started



Related: 10 Redshift Create table examples

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