Infrastructure as Code (IaC) is a method of managing and provisioning infrastructure through machine-readable definition files, rather than physical hardware configuration or interactive configuration tools. This approach enables developers and operations teams to automate the process of infrastructure deployment, scaling, and management, reducing the risk of human error and increasing efficiency.

One of the key challenges in managing infrastructure with IaC is state management. In this context, state refers to the current configuration of the infrastructure, including the versions of software installed, the network configuration, and the security settings. As infrastructure changes over time, it is essential to keep track of the current state to ensure that the infrastructure is configured correctly and that changes are made in a controlled and predictable manner.

There are several approaches to state management in IaC, each with its own advantages and disadvantages. In this blog post, we will explore three common approaches: imperative, declarative, and hybrid.

Imperative State Management

Imperative state management is an approach in which the infrastructure is managed by specifying a series of commands or actions to be executed in order to achieve the desired state. This approach is similar to traditional scripting, in which a series of commands are executed in order to configure the infrastructure.

Here is an example of an imperative IaC script using the CloudFormation template language:

Resources:
  MyEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: ami-0c94855ba95c574c8
      InstanceType: t2.micro
      SecurityGroupIds:
        - !Ref MySecurityGroup
      KeyName: my-key-pair
      UserData:
        Fn::Base64:
          !Sub |
            #!/bin/bash
            yum update -y
            yum install -y httpd
            systemctl start httpd
            systemctl enable httpd
            echo "Hello, World!" > /var/www/html/index.html

In this example, the script creates an EC2 instance, installs the Apache web server, and starts the service. The state of the infrastructure is managed by executing these commands in order.

The main advantage of imperative state management is that it is simple and easy to understand. It is also flexible, as it allows for the execution of arbitrary commands to configure the infrastructure. However, it has several disadvantages. First, it is difficult to maintain and update, as changes to the infrastructure require modifying the script. Second, it is difficult to track the current state of the infrastructure, as it is not explicitly defined in the script. Finally, it is difficult to roll back changes, as there is no record of the previous state of the infrastructure.

Declarative State Management

Declarative state management is an approach in which the infrastructure is managed by specifying the desired state, rather than the actions required to achieve that state. This approach is similar to a configuration file, in which the desired state of the infrastructure is defined.

Here is an example of a declarative IaC script using the Terraform configuration language:

resource "aws_instance" "example" {
  ami           = "ami-0c94855ba95c574c8"
  instance_type = "t2.micro"

  vpc_security_group_ids = [aws_security_group.example.id]

  key_name = "my-key-pair"

  user_data = <<-EOF
              #!/bin/bash
              yum update -y
              yum install -y httpd
              systemctl start httpd
              systemctl enable httpd
              echo "Hello, World!" > /var/www/html/index.html
              EOF

  tags = {
    Name = "example-instance"
  }
}

resource "aws_security_group" "example" {
  name        = "example-security-group"
  description = "Example security group"

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "example-security-group"
  }
}

In this example, the script defines the desired state of the infrastructure, including an EC2 instance and a security group. The state of the infrastructure is managed by comparing the desired state with the current state, and making any necessary changes to bring the infrastructure into the desired state.

The main advantage of declarative state management is that it is easy to maintain and update, as changes to the infrastructure can be made by modifying the configuration file. It is also easy to track the current state of the infrastructure, as it is explicitly defined in the configuration file. Finally, it is easy to roll back changes, as the previous state of the infrastructure is stored in the configuration file.

However, declarative state management has several disadvantages. First, it can be more difficult to understand than imperative state management, as it requires a different way of thinking about infrastructure management. Second, it can be less flexible than imperative state management, as it does not allow for the execution of arbitrary commands to configure the infrastructure.

Hybrid State Management

Hybrid state management is an approach that combines elements of both imperative and declarative state management. In this approach, the infrastructure is managed by specifying both the desired state and the actions required to achieve that state.

Here is an example of a hybrid IaC script using the Ansible playbook language:

- name: Provision EC2 instance
  amazon.aws.ec2_instance:
    image_id: ami-0c94855ba95c574c8
    instance_type: t2.micro
    security_groups:
      - example-security-group
    key_name: my-key-pair
    wait: yes
  register: ec2_instance

- name: Install Apache web server
  become: yes
  amazon.aws.amazon_linux_extras:
    name: httpd
    state: present
  when: ec2_instance.instance_id is defined

- name: Start Apache web server
  service:
    name: httpd
    state: started
    enabled: yes
  when: ec2_instance.instance_id is defined

- name: Create index.html file:
path: /var/www/html/index.html
state: touch
content: "Hello, World!"
when: ec2\_instance.instance\_id is defined

vbnet

In this example, the script uses the amazon.aws.ec2_instance module to create an EC2 instance, and the amazon.aws.amazon_linux_extras and service modules to install and start the Apache web server. The state of the infrastructure is managed by specifying both the desired state (e.g., the EC2 instance and the Apache web server) and the actions required to achieve that state (e.g., installing the Apache web server and starting the service).

The main advantage of hybrid state management is that it combines the flexibility of imperative state management with the ease of maintenance and tracking of declarative state management. It allows for the execution of arbitrary commands to configure the infrastructure, while also providing a clear and explicit definition of the desired state.

However, hybrid state management has several disadvantages. First, it can be more complex than either imperative or declarative state management, as it requires the use of multiple modules and commands to manage the infrastructure. Second, it can be more difficult to understand, as it requires a combination of imperative and declarative thinking.

Conclusion

State management is a critical aspect of infrastructure management with IaC. There are several approaches to state management, each with its own advantages and disadvantages. Imperative state management is simple and flexible, but difficult to maintain and track. Declarative state management is easy to maintain and track, but less flexible and more difficult to understand. Hybrid state management combines the flexibility of imperative state management with the ease of maintenance and tracking of declarative state management, but can be more complex and difficult to understand.

Ultimately, the choice of state management approach will depend on the specific needs and requirements of the infrastructure being managed. It is important to carefully consider the advantages and disadvantages of each approach, and to choose the one that best meets the needs of the organization.