AWS CloudFormation For Beginners with Examples

In this blog, we will explore AWS CloudFormation with examples.

Check out my Youtube video on this article.

Prerequisite

Clone this git repo
AWS Account Setup

Agenda:

CloudFormation Concepts (Stacks & ChangeSet)
Parameters
Mappings
Conditions
Outputs

AWS CloudFormation is used to describe and provision all of the infrastructure resources in your cloud environment.

This is an “Infrastructure as Code” which means that you are writing a code to create your infrastructure
it is repeatable and also version-able because you can store your code in your git repo.
So to create an infrastructure on AWS you actually create a CloudFormation template.

AWS CloudFormation Concepts

Stack

To create a resources we actually create a stack

In the stack, you actually provide a template( Cloudformation template) which contains all the code to provision your resources like AWS EC2, VPC etc.

2. ChangeSet

You can see what all changes will be made when you run this template. You can say like a dry run before actually creating a resources

Here you can see that what all changes will be deploying with this template

NOTE:

There are several properties in Amazon Relational Database Service (Amazon RDS) instances that AWS CloudFormation modifies and requires replacement in the underlying database instance resource. If backups are not being taken, data loss will occur. You use a change set to preview the replacement event, make the necessary backups, and take the required precautions before you update the resources.

Permissions

You can use an IAM user or a role to create a template. IAM user or role should have the permission to create whatever you are provisioning from your cloudformation template.

If you submit the template as a local file, it uploads to Amazon S3 on your behalf. Because of this, you must add these permissions to create a stack:

cloudformation:CreateUploadBucket
s3:PutObject
s3:ListBucket
s3:GetObject
s3:CreateBucket

AWS Template Structure

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "String Description",
  "Metadata": { },
  "Parameters": { },
  "Mappings": { },
  "Conditions": { },
  "Transform": { },
  "Resources": { },
  "Outputs": { }
}

AWS CloudFormation requires only the Resources section.

If you do not define Resource section then you will see the below error

Template format error: At least one Resources member must be defined.

Parameters

Parameters — You can provide the input parameters while creating/updating a stack

Each parameter must be given a logical name (also called logical ID like InstanceTypeParameter), which must be alphanumeric and unique among all logical names within the template.

For the sensitive parameter like password, you can add the NoEcho property. When this is set, the parameter value displays as asterisks (***) for any cloudformation:Describe* calls.

AWS CloudFormation supports the following parameter types:

String
Number
List of numbers
Comma-delimited list
AWS parameter types — Like Amazon EC2 key pair names, IDs of resources, AWS regions/availability zones which are already exist in your account so instead of user provides these value manually , cloudformation template automatically get these properties from your AWS account
AWS System Manager parameter types AWS Systems Manager parameter types can reference parameters that exist in the AWS Systems Manager Parameter Store. If you specify a parameter key, AWS CloudFormation will search your Systems Manager Parameter Store for the correct value and input this into the stack

In the below example we will provide following parameters

what type of instance you want to create
create an ec2 instance for that particular type only.
Ask the DB password
All keys from your AWS account will come in the dropdown
How to refer the parameters in a template

AWSTemplateFormatVersion: 2010-09-09
Resources:
 Ec2Instance:
  Type: AWS::EC2::Instance
  Properties:
    InstanceType:
      Ref: InstanceTypeParameter1
    ImageId: ami-01aab85a5e4a5a0fe
Parameters:
  InstanceTypeParameter1:
    Type: String
    Default: t2.micro
    AllowedValues:
      - t2.micro
      - m1.small
      - m1.large
    Description: Enter t2.micro, m1.small, or m1.large. Default is t2.micro.
  DBPort: 
    Default: 3306
    Description: TCP/IP port for the database
    Type: Number
    MinValue: 1150
    MaxValue: 65535
  DBPwd: 
    NoEcho: true
    Description: The database admin account password
    Type: String
    MinLength: 1
    MaxLength: 41
  myKeyPair: 
    Description: Amazon EC2 Key Pair
    Type: "AWS::EC2::KeyPair::KeyName"

Mappings

Mappings used to matches a key to a corresponding set of named values.

Create a mapping that will look for Amazon EC2 instance AMI IDs based on the region and architecture type

The below example –

Creating a mapping of EC2 AMI’s based on the region and type
Creating an EC2 instance ( finding the region automatically and based on that it will find the AMI ID from the mapping)
The AWS::Region reference is a pseudoparameter that means it’s a parameter that AWS defines automatically on your behalf.

AWSTemplateFormatVersion: "2010-09-09"
Mappings: 
  RegionMap: 
    us-east-2:
      HVM64: ami-01aab85a5e4a5a0fe
      HVMG2: ami-0a584ac55a7631c0c
    us-west-1:
      HVM64: ami-0bdb828fd58c52235
      HVMG2: ami-066ee5fd4a9ef77f1
    eu-west-1:
      HVM64: ami-047bb4163c506cd98
      HVMG2: ami-0a7c483d527806435
    ap-northeast-1:
      HVM64: ami-06cd52961ce9f0d85
      HVMG2: ami-053cdd503598e4a9d
    ap-southeast-1:
      HVM64: ami-08569b978cc4dfa10
      HVMG2: ami-0be9df32ae9f92309
Resources: 
  myEC2Instance: 
    Type: "AWS::EC2::Instance"
    Properties: 
      ImageId: !FindInMap [RegionMap, !Ref "AWS::Region", HVM64]
      InstanceType: t2.micro

Conditions

We define conditions when to create a resource. We use intrinsic functions to evaluate multiple inputs against one another

For Ex-

Create a larger EC2 instance when environment is production

Create a volume only when the environment is production

AWSTemplateFormatVersion: 2010-09-09
Parameters:
  EnvType:
    Description: Environment type.
    Default: test
    Type: String
    AllowedValues:
      - prod
      - test
    ConstraintDescription: must specify prod or test.
Conditions:
  CreateProdResources: !Equals 
    - !Ref EnvType
    - prod
Resources:
  EC2Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      ImageId: ami-01aab85a5e4a5a0fe
      InstanceType: t2.micro
  MountPoint:
    Type: 'AWS::EC2::VolumeAttachment'
    Condition: CreateProdResources
    Properties:
      InstanceId: !Ref EC2Instance
      VolumeId: !Ref NewVolume
      Device: /dev/sdh
  NewVolume:
    Type: 'AWS::EC2::Volume'
    Condition: CreateProdResources
    Properties:
      Size: 100
      AvailabilityZone: !GetAtt 
        - EC2Instance
        - AvailabilityZone

Outputs

Outputs are used to refer some values outside a single stack.

For Ex –

cross-stack references
nested stacks
describe-stack API calls,
AWS CloudFormation console.

In this example-

the output named StackEC2 returns the ID of a EC2, and then exports the value for cross-stack referencing with the name EC2 appended to the stack’s name. (Cross stack reference)
the output named InstanceID returns the ID of EC2

AWSTemplateFormatVersion: "2010-09-09"
Mappings: 
  RegionMap: 
    us-east-2:
      HVM64: ami-01aab85a5e4a5a0fe
      HVMG2: ami-0a584ac55a7631c0c
Resources: 
  myEC2Instance: 
    Type: "AWS::EC2::Instance"
    Properties: 
      ImageId: !FindInMap [RegionMap, !Ref "AWS::Region", HVM64]
      InstanceType: t2.micro
Outputs:
   InstanceID:
    Description: The Instance ID
    Value: !Ref myEC2Instance
   StackEC2:
    Description: The ID of the EC2 Instance
    Value: !Ref myEC2Instance
    Export:
      Name: !Sub "${AWS::StackName}-EC2"

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