Demo Managing and working with multiple regions Part 1

In this lesson we’ll cover how to manage EC2 AMI selection across multiple AWS regions using a CloudFormation mapping. Instead of hard-coding an ImageId in your template, define a Mappings section keyed by AWS region codes and use Fn::FindInMap (short form: !FindInMap) with the AWS::Region pseudo parameter so CloudFormation automatically picks the correct AMI for the region where the stack is created. Problem: a template that hard-codes an AMI (region-specific)

Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref MyInstanceType
      ImageId: ami-0eb9d6fc9fab44d24
      SecurityGroupIds:
        - !Ref MySecurityGroup
      Tags:
        - Key: Name
          Value: SimpleWebServer
      UserData:
        Fn::Base64: |
          #!/bin/bash
          yum update -y

Hard-coding an AMI prevents the template from working across regions because AMI IDs differ between regions. The solution is to maintain a mapping of region → AMI and look up the AMI at stack creation time. Step 1 — Create a region-to-AMI mapping (near top of the template)

Mappings:
  RegionMap:
    us-east-2:
      AMI: ami-0eb9d6fc9fab44d24
    eu-west-1:
      AMI: ami-0b3e7dd7b2a99b08d
    us-east-1:
      AMI: ami-0150ccaf51ab55a51

To collect the AMI values, switch the EC2 console to each target region (for example, eu-west-1, us-east-1, etc.) and copy the AMI ID for the Amazon Linux or other base image you intend to use.

A browser screenshot of the AWS EC2 "Launch an instance" console with the Amazon Linux 2023 AMI selected, showing AMI details (architecture, boot mode, AMI ID) and description. The right-hand Summary panel lists the instance count, instance type (t3.micro), security group and a "Launch instance" button.

Repeat this for each region you want to support so your mapping contains one entry per region, keyed by the exact AWS region code (for example, us-east-2, eu-west-1, us-east-1).

A web browser screenshot of the Amazon Web Services EC2 dashboard showing the "Resources" panel listing EC2 items (Instances, Security groups, Elastic IPs, Load balancers, etc.) for the US-East-2 (Ohio) region. The lower panels show "Launch instance" and "Service health" options.

Step 2 — Use Fn::FindInMap with the AWS::Region pseudo parameter Replace the ImageId property with a FindInMap lookup so CloudFormation uses the mapping keyed by the current region:

Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref MyInstanceType
      ImageId: !FindInMap [RegionMap, !Ref "AWS::Region", AMI]
      SecurityGroupIds:
        - !Ref MySecurityGroup
      Tags:
        - Key: Name
          Value: SimpleWebServer
      UserData:
        Fn::Base64: |
          #!/bin/bash
          yum update -y

CloudFormation evaluates !Ref “AWS::Region” at stack creation, finds the matching top-level key in RegionMap, and returns the AMI value. Keys must exactly match the region codes returned by AWS::Region (case-sensitive and lowercase). Consolidated example template

Metadata:
  Purpose: Basic EC2 instance with HTTP and SSH access

Mappings:
  RegionMap:
    us-east-2:
      AMI: ami-0eb9d6fc9fab44d24
    eu-west-1:
      AMI: ami-0b3e7dd7b2a99b08d
    us-east-1:
      AMI: ami-0150ccaf51ab55a51

Parameters:
  MyInstanceType:
    Type: String
    Description: Select your EC2 instance type
    AllowedValues:
      - t3.micro
      - t3.small
  MyVPC:
    Type: AWS::EC2::VPC::Id
    Description: Select the VPC to launch the EC2 instance in
  MySecurityGroup:
    Type: AWS::EC2::SecurityGroup::Id
    Description: Select a Security Group to attach to the instance

Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref MyInstanceType
      ImageId: !FindInMap [RegionMap, !Ref "AWS::Region", AMI]
      SecurityGroupIds:
        - !Ref MySecurityGroup
      Tags:
        - Key: Name
          Value: SimpleWebServer
      UserData:
        Fn::Base64: |
          #!/bin/bash
          yum update -y
          yum install -y httpd
          systemctl enable --now httpd
          echo "Hello from $(hostname -f)" > /var/www/html/index.html

A screenshot of the AWS Management Console showing the CloudFormation "Stacks" page with one stack named "DemoStack" marked UPDATE_COMPLETE. The region selector is open and highlights the United States (Ohio) us-east-2 region.

Deployment notes and best practices

If you change the mapping or the AMI used by an instance, you will usually need to delete and recreate the instance (or perform a stack update that replaces the instance) for the new AMI to be used.
Keep the Mappings section near the top of the template for easier maintenance.
Validate that mapping keys exactly match the AWS::Region values (e.g., us-east-2, eu-west-1).
Periodically refresh the AMI IDs in your mapping to pick up updated OS images or security fixes.

Quick reference: mapping usage

Concept	Purpose	Example
Mappings section	Store per-region configuration values (e.g., AMI IDs)	RegionMap: us-east-2 → AMI
Fn::FindInMap / !FindInMap	Retrieve a mapped value at runtime	!FindInMap [RegionMap, !Ref “AWS::Region”, AMI]
AWS::Region (pseudo parameter)	Returns the region where the stack is created	!Ref “AWS::Region”

When maintaining mappings, periodically verify AMI IDs in each region — AMI IDs differ between regions and may change with new OS releases. Ensure mapping keys are exact region codes (lowercase).

Links and references

CloudFormation Mappings and Intrinsic Functions: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/mappings-section-structure.html
Fn::FindInMap: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-findinmap.html
AWS::Region pseudo parameter: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/pseudo-parameter-reference.html
EC2 console: https://console.aws.amazon.com/ec2/
Learn more: CloudFormation course at KodeKloud and EC2 course at KodeKloud

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Demo Replacing hardcoded values with a pseudo parameter

Demo Managing and working with multiple regions Part 2

Course Introduction

Cloud Service Models

Code Editor Setup and Source Code

AWS CloudFormation Introduction

Resources

From Template to Stack

Metadata and Tags

Intrinsic Functions

Parameters

Mappings

CloudFormation - Conditions and Policies

Outputs

Infrastructure Composer

EC2 Instance Setup With an HTTP Server

AWS CLI

Access Control

Drift Detection

Nested Stacks

StackSets

Deployment Modes

SSM Parameters

CFN init and Resource Imports

Automation and Integration

Registry

Conclusion

Demo Managing and working with multiple regions Part 1

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