CloudFormation - Mappings

Mappings are fixed values in the CloudFormation template specified in key-value format. To access the mapping values, use Fn::FindInMap.

!FindInMap[MapName, TopLevelKey, SecondLevelKey]

example: !FindInMap [environmentMap, dev, ami]

AWSTemplateFormatVersion: 2010-09-09

Parameters: 
    env:
      Description: "Enter Environment: (dev/prod)"
      Type: String

Mappings: 
    environmentMap:
        dev:
          instype : "t2.micro"
          ami: "ami-0c6120f461d6b39e9"
        prod:
          instype: "t2.small"
          ami: "ami-0a443decce6d88dc2"

Resources: 
    AppServer:
      Type: 'AWS::EC2::Instance'
      Properties:
       ImageId: !FindInMap [environmentMap, !Ref env, ami]
       InstanceType: !FindInMap [environmentMap, !Ref env, instype]
       SecurityGroups: 
          - "sshSG"
       Tags:
         -  Key: "Name"
            Value: !Sub 
                    - '${environment}_server'
                    - environment: !Ref env

In the above template, the mapping "environmentMap" has two Top Level Keys [dev/prod]. Based on the input parameter passed (dev/prod), the instance is created with the corresponding mapping values for ami & instance type.

aws cloudformation create-stack --stack-name myteststack1 --template-body file:///home/ec2-user/CF_Learnings/004_Mappings/mappings.yaml --region ap-southeast-2 --parameters ParameterKey=env,ParameterValue=prod

In the input parameter, we specified environment parameter value to be "prod " and hence appropriate ImageId & InstanceType are chosen from the mapping defined for "prod".