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Showing content from https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/mappings-section-structure.html below:

CloudFormation template Mappings syntax - AWS CloudFormation

CloudFormation template Mappings syntax

The optional Mappings section helps you create key-value pairs that can be used to specify values based on certain conditions or dependencies.

One common use case for the Mappings section is to set values based on the AWS Region where the stack is deployed. This can be achieved by using the AWS::Region pseudo parameter. The AWS::Region pseudo parameter is a value that CloudFormation resolves to the region where the stack is created. Pseudo parameters are resolved by CloudFormation when you create the stack.

To retrieve values in a map, you can use the Fn::FindInMap intrinsic function within the Resources section of your template.

Syntax

The Mappings section uses the following syntax:

JSON

"Mappings" : {
  "MappingLogicalName" : {
    "Key1" : {
      "Name" : "Value1"
    },
    "Key2" : {
      "Name" : "Value2"
    },
    "Key3" : {
      "Name" : "Value3"
    }
  }
}

YAML

Mappings: 
  MappingLogicalName: 
    Key1: 
      Name: Value1
    Key2: 
      Name: Value2
    Key3: 
      Name: Value3

MappingLogicalName is the logical name for the mapping.
Within the mapping, each map is a key followed by another mapping.
The key must be a map of name-value pairs and unique within the mapping.
The name-value pair is a label, and the value to map. By naming the values, you can map more than one set of values to a key.
The keys in mappings must be literal strings.
The values can be of type String or List.

Note

You can't include parameters, pseudo parameters, or intrinsic functions in the Mappings section.

If the values in a mapping aren't currently used by your stack, you cannot update the mapping alone. You must include changes that add, modify, or delete resources.

Examples Basic mapping

The following example shows a Mappings section with a map RegionMap, which contains five keys that map to name-value pairs containing single string values. The keys are region names. Each name-value pair is an instance type from the T family that's available in the region represented by the key. The name-value pairs have a name (InstanceType in the example) and a value.

JSON

"Mappings" : {
  "RegionMap" : {
    "us-east-1"      : {"InstanceType": "t2.micro"},
    "us-west-1"      : {"InstanceType": "t2.micro"},
    "eu-west-1"      : {"InstanceType": "t2.micro"},
    "eu-north-1"     : {"InstanceType": "t3.micro"},
    "me-south-1"     : {"InstanceType": "t3.micro"}
  }
}

YAML

Mappings:
  RegionMap:
    us-east-1:
      InstanceType: t2.micro
    us-west-1:
      InstanceType: t2.micro
    eu-west-1:
      InstanceType: t2.micro
    eu-north-1:
      InstanceType: t3.micro
    me-south-1:
      InstanceType: t3.micro

Mapping with multiple values

The following example has region keys that are mapped to two sets of values: one named MyAMI1 and the other MyAMI2.

JSON

    "AMIIDMap" : {
      "us-east-1"        : {"MyAMI1" : "ami-0ff8a91507f77f867", "MyAMI2" : "ami-0a584ac55a7631c0c"},
      "us-west-1"        : {"MyAMI1" : "ami-0bdb828fd58c52235", "MyAMI2" : "ami-066ee5fd4a9ef77f1"},
      "eu-west-1"        : {"MyAMI1" : "ami-047bb4163c506cd98", "MyAMI2" : "ami-0a7c483d527806435"},
      "ap-southeast-1"   : {"MyAMI1" : "ami-08569b978cc4dfa10", "MyAMI2" : "ami-0be9df32ae9f92309"},
      "ap-northeast-1"   : {"MyAMI1" : "ami-06cd52961ce9f0d85", "MyAMI2" : "ami-053cdd503598e4a9d"}
    }

YAML

AMIIDMap: 
    us-east-1:
      MyAMI1: ami-0ff8a91507f77f867
      MyAMI2: ami-0a584ac55a7631c0c
    us-west-1:
      MyAMI1: ami-0bdb828fd58c52235
      MyAMI2: ami-066ee5fd4a9ef77f1
    eu-west-1:
      MyAMI1: ami-047bb4163c506cd98
      MyAMI2: ami-0a7c483d527806435
    ap-southeast-1:
      MyAMI1: ami-08569b978cc4dfa10
      MyAMI2: ami-0be9df32ae9f92309
    ap-northeast-1:
      MyAMI1: ami-06cd52961ce9f0d85
      MyAMI2: ami-053cdd503598e4a9d

Return a value from a mapping

You can use the Fn::FindInMap function to return a named value based on a specified key. The following example template contains an Amazon EC2 resource whose ImageId property is assigned by the FindInMap function. The FindInMap function specifies key as the region where the stack is created (using the AWS::Region pseudo parameter) and MyAMI1 as the name of the value to map to. For more information about pseudo parameters, see Get AWS values using pseudo parameters.

JSON

{
  "AWSTemplateFormatVersion" : "2010-09-09",
  "Mappings" : {
    "AMIIDMap" : {
      "us-east-1"        : {"MyAMI1" : "ami-0ff8a91507f77f867", "MyAMI2" : "ami-0a584ac55a7631c0c"},
      "us-west-1"        : {"MyAMI1" : "ami-0bdb828fd58c52235", "MyAMI2" : "ami-066ee5fd4a9ef77f1"},
      "eu-west-1"        : {"MyAMI1" : "ami-047bb4163c506cd98", "MyAMI2" : "ami-0a7c483d527806435"},
      "ap-northeast-1"   : {"MyAMI1" : "ami-06cd52961ce9f0d85", "MyAMI2" : "ami-053cdd503598e4a9d"},
      "ap-southeast-1"   : {"MyAMI1" : "ami-08569b978cc4dfa10", "MyAMI2" : "ami-0be9df32ae9f92309"}
    }
  },
  "Resources" : {
    "myEC2Instance" : {
      "Type" : "AWS::EC2::Instance",
      "Properties" : {
        "ImageId" : { "Fn::FindInMap" : [ "AMIIDMap", { "Ref" : "AWS::Region" }, "MyAMI1" ]},
        "InstanceType" : "t2.micro"
      }
    }
  }
}

YAML

AWSTemplateFormatVersion: 2010-09-09
Mappings: 
  AMIIDMap: 
    us-east-1:
      MyAMI1: ami-0ff8a91507f77f867
      MyAMI2: ami-0a584ac55a7631c0c
    us-west-1:
      MyAMI1: ami-0bdb828fd58c52235
      MyAMI2: ami-066ee5fd4a9ef77f1
    eu-west-1:
      MyAMI1: ami-047bb4163c506cd98
      MyAMI2: ami-0a7c483d527806435
    ap-northeast-1:
      MyAMI1: ami-06cd52961ce9f0d85
      MyAMI2: ami-053cdd503598e4a9d
    ap-southeast-1:
      MyAMI1: ami-08569b978cc4dfa10
      MyAMI2: ami-0be9df32ae9f92309
Resources: 
  myEC2Instance: 
    Type: "AWS::EC2::Instance"
    Properties: 
      ImageId: !FindInMap [AMIIDMap, !Ref "AWS::Region", MyAMI1]
      InstanceType: t2.micro

Input parameter and Fn::FindInMap

You can use an input parameter with the Fn::FindInMap function to refer to a specific value in a map. For example, suppose you have a list of regions and environment types that map to a specific security group ID. You can select the security group ID that your stack uses by using an input parameter (EnvironmentType). To determine the region, use the AWS::Region pseudo parameter, which gets the AWS Region in which you create the stack.

This example also declares a Systems Manager parameter type that provides a Systems Manager parameter alias (/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2) as the default value for the ImageId property of the EC2 instance. This is a value that CloudFormation resolves as the AMI ID value for the latest Amazon Linux 2 AMI in the region where the stack is created.

JSON

{
  "AWSTemplateFormatVersion" : "2010-09-09",
  "Parameters" : {
    "LatestAmiId" : {
      "Description" : "The latest Amazon Linux 2 AMI from the Parameter Store",
      "Type" : "AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>",
      "Default" : "/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2"
    },
    "EnvironmentType" : {
      "Description" : "The environment type (Dev or Prod)",
      "Type" : "String",
      "Default" : "Dev",
      "AllowedValues" : [
        "Dev",
        "Prod"
      ]
    }
  },
  "Mappings" : {
    "SecurityGroupMap" : {
      "us-east-1" : {
        "Dev" : "sg-12345678",
        "Prod" : "sg-abcdef01"
      },
      "us-west-2" : {
        "Dev" : "sg-ghijkl23",
        "Prod" : "sg-45678abc"
      }
    }
  },
  "Resources" : {
    "Ec2Instance" : {
      "Type" : "AWS::EC2::Instance",
      "Properties" : {
        "ImageId" : {
          "Ref" : "LatestAmiId"
        },
        "InstanceType" : "t2.micro",
        "SecurityGroupIds" : [{ "Fn::FindInMap" : [ "SecurityGroupMap", { "Ref" : "AWS::Region" }, { "Ref" : "EnvironmentType" } ]}]
      }
    }
  }
}

YAML

AWSTemplateFormatVersion: 2010-09-09
Parameters:
  LatestAmiId:
    Description: The latest Amazon Linux 2 AMI from the Parameter Store
    Type: 'AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>'
    Default: '/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2'
  EnvironmentType: 
    Description: The environment type (Dev or Prod)
    Type: String
    Default: Dev
    AllowedValues: 
      - Dev
      - Prod
Mappings: 
  SecurityGroupMap: 
    us-east-1: 
      Dev: "sg-12345678"
      Prod: "sg-abcdef01"
    us-west-2: 
      Dev: "sg-ghijkl23"
      Prod: "sg-45678abc"
Resources:
  Ec2Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      ImageId: !Ref LatestAmiId
      InstanceType: t2.micro
      SecurityGroupIds:
        - !FindInMap [SecurityGroupMap, !Ref "AWS::Region", !Ref EnvironmentType]

These related topics can be helpful as you develop templates that use the Fn::FindInMap function.

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