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Infrastructure as code (IaC)


Infrastructure as Code (IaC)


This blog provides a demonstration of Infrastructure as Code, where we will deploy an EC2 instance using a CloudFormation template.

Infrastructure as code

Infrastructure as code, also known as IaC, is a process of managing IT infrastructure through configuration files. Infrastructure as code enables developers to manage, monitor and provision resources using machine readable files. This avoids having to manually configure various hardware devices and operating systems. The code can be thought to be similar to programming scripts which are used to automate IT processes.

In the past, managing IT infrastructure was a manual, error prone, and time consuming process. Operators would physically install servers in place. The servers were then configured with the required settings and software to run an application.

With the growth of cloud infrastructure, service provider companies now have easier access to servers. However, servers still need to be provisioned and configured to run the required software. Any manual steps involved in this process can result in issues in three main areas: cost, scalability and availability.

Automating infrastructure provisioning with IaC means that developers don’t need to manually provision and manage servers, operating systems, storage, and other infrastructure components each time an application needs to be developed or deployed.

What is CloudFormation?

The cloud infrastructure hosted using Amazon Web Services can be managed using an IaC software called CloudFormation. Using CloudFormation, developers can define templates that describe the AWS resources such as EC2 instances or RDS. CloudFormation takes care of actually provisioning and configuring the resources based on the information in the template.


Templates : A CloudFormation template is text file written in JSON or YAML format. The templates inform AWS CloudFormation of the AWS resources that need to be provisioned. For example, a template can describe an EC2 instance with the AMI ID, instance size, key pair mapping, storage size, etc.

Stacks : All the resources defined in one template file are managed as a single unit called a stack. Resources can be created, updated or deleted by creating, updating, or deleting stacks.

Change sets : We can make changes to the resource by updating the stack. Before a change can be made, a change set is generated. A change set describes a summary of proposed changes. They allow the developer to check how the changes being made might impact the running resources and services. Some of changes might result in downtime. For example, changing the name of an RDS instance after provisioning results in a change set where CloudFormation will create a new database and remove the old one. The result will be loss of all data in the old database unless it was backed up.

Version control

Version control is an important part of IaC. We will use GitHub Actions to create a deployment using CloudFormation. If you are unfamiliar with GitHub Actions, the blog here will be helpful.

To follow along with our demonstration, you will need:

  1. A GitHub account
  2. An AWS account

Navigating to CloudFormation in AWS

  1. Login to AWS with the credentials given to you. If you cannot access CloudFormation, check with your AWS account administrator.
  2. Find CloudFormation under Services tab.
  3. Click on Stacks from the menu on the left.
All the stacks provisioned are shown here.

Provisioning instances using Actions

AWS Setup

In order to provision the resources using Actions, create an IAM User and store the AWS access key and secret key in GitHub.

To add secrets, click on the repository, Settings tab -> Secrets.

Additionally, create a key pair in AWS. To create a key pair.

  1. Under the Services tab, select EC2.
  2. From the EC2 Dashboard, click on Key Pairs option under Network & Security.
  3. Click on Create key pair.
  4. Give the KeyPair a name DemoKey. Select the format of the download the key and save it a at a safe location.

CloudFormation template

The template demo.yml available here creates a new VPC. The snippet from the YAML file shown below defines the resource type. Each resource is given a set of properties. For the type AWS::EC2::VPC, the required properties are CidrBlock which defines the IP CIDR range for the VPC in the AWS cloud environment. Additional properties can be defined to override the defaults as required. The complete set of documentation can be found here.

    Type: AWS::EC2::VPC
    DeletionPolicy: Retain
      CidrBlock: !Ref 'VpcCIDRBlock'
      EnableDnsSupport: true
      EnableDnsHostnames: true
      InstanceTenancy: default
        - Key: Name
          Value: DemoVPC 

Also, demo.yml creates a subnet within the VPC:

    Type: AWS::EC2::Subnet
          - 0
          - Fn::GetAZs: ""
        Ref: VPC
      CidrBlock: !Ref 'SubnetCIDRBlock'
        - Key: Name
          Value: DemoSubnet 

defines security group rules:

    Type: 'AWS::EC2::SecurityGroup'
      GroupDescription: DemoSG
      VpcId: !Ref VPC
      - IpProtocol: tcp
        FromPort: 22
        ToPort: 22
        CidrIp: ''
      - IpProtocol: icmpv6
        FromPort: -1
        ToPort: -1       
        CidrIp: '' 

and finally provisions an EC2 machine with Ubuntu 18.04:

    Type: AWS::EC2::Instance
      KeyName: 'DemoKey'
      ImageId: !Ref ImageID
      InstanceType: t2.micro
        - AssociatePublicIpAddress: "true"
          DeviceIndex: "0"
            - Ref: DemoSG
            Ref: "DemoSubnet"
        Fn::Base64: !Sub |
                   wget -O /tmp/amazon-cloudwatch-agent.deb
                   dpkg -i /tmp/amazon-cloudwatch-agent.deb
                   apt-get update -y
                   apt-get  install -y python-pip
                   easy_install --script-dir /opt/aws/bin
                   /opt/aws/bin/cfn-init -v --stack ${AWS::StackId} --resource EC2Instance --region ${AWS::Region} --configsets default
                   /opt/aws/bin/cfn-signal -e $? --stack ${AWS::StackId} --resource EC2Instance --region ${AWS::Region}      
        - Key: Name
          Value: DemoBastionInstance 

To run the workflow, make sure you provide the required properties for each resource.

Finally, Parameters can be used to pass variable values to the template.

    Description: 'AWS Amazon Machine Image ID'
    Type: String
    Default: 'ami-063e88ad6c9af427d'
    Description: 'CIDR Block for VPC Ex.'
    Type: String
    Description: 'CIDR Block for public subnet Ex.'
    Type: String

GitHub Actions

We have two workflows in the repository – DeployOrModify and DeleteStack.


This workflow can be used to deploy a new stack or modify an existing stack.

To deploy the template, navigate to the Actions tab in GitHub and select the workflow to run. Give the inputs required or use the defaults.

  • AWS Amazon Machine Image ID: The AMI ID for the EC2 server.
  • CIDR Block for VPC: The VPC CIDR range to deploy the EC2 server in.
  • CIDR Block for subnet: The CIDR range of the subnet where the EC2 server will be deployed.
  • Stack template relative path: The CloudFormation template file name to deploy/modify.
  • Stack name: The CloudFormation stack name to deploy/modify.
  • Enter 0 to execute immediately else 1: The value 0 attempts to execute the changes to the stack immediately. The value 1 would create a change set that can be viewed and executed from AWS CloudFormation.

Click on Run workflow.

If 1 was entered above in Enter 0 to execute immediately else 1 option, then click on the Stack name in CloudFormation Stacks list, and then click on the Change sets tab.

Click on the Change set, verify the changes being made to the stack, and click on Execute if the change set is as expected.

CloudFormation events and progress are shown upon selection of the stack. Create Complete indicates successful completion of changes.

A successful run will deploy the EC2 instance to your AWS account.


The networking components VPC details (subnet as well as the security group) will also be created as defined in the template.



Use the DeleteStack workflow only if you are sure that all the resources related to the stack can be deleted. To clean up the instance provisioned above, Run the workflow to remove the resources created.

Managing drifts

Stack drift is when the template doesn’t represent the state of AWS infrastructure that actually exists. Drifts can be resolved either by importing new resources or using an update action. Managing drifts is beyond the scope of this blog but it is something to be aware of as one starts managing their infrastructure using CloudFormation or any other IaC service.


This blog explained the steps involved in deploying AWS infrastructure – VPC, subnet and EC2 servers – using CloudFormation and GitHub Actions. Please contact us if you have any questions about this blog or any other DevOps topics you want us write about.