Implement and Manage Configuration Changes

Key Concepts

• Configuration Management: Ensuring systems are consistently configured and maintained according to predefined standards.
• Desired State Configuration (DSC): Defining and maintaining the desired state of infrastructure.
• Idempotency: The property of certain operations that can be applied multiple times without changing the result beyond the initial application.
• Configuration Drift: The phenomenon where the actual state of a system diverges from its desired state.
• Automated Remediation: Automatically correcting configuration drift to maintain the desired state.

Detailed Explanation

Configuration Management

Configuration management involves ensuring that systems and applications are consistently configured and maintained according to predefined standards. This process helps in reducing errors, ensuring compliance, and maintaining system reliability.

Desired State Configuration (DSC)

DSC is a method of defining the desired state of infrastructure and ensuring that the actual state matches this desired state. Tools like AWS Systems Manager and Puppet use DSC to enforce configurations and maintain system integrity.

Idempotency

Idempotency ensures that a configuration change can be applied multiple times without causing unintended side effects. For example, if you want to ensure that a package is installed, an idempotent operation will install the package only if it is not already installed.

Configuration Drift

Configuration drift occurs when the actual state of a system diverges from its desired state over time due to manual changes, updates, or other factors. Configuration management tools help detect and correct drift to maintain consistency.

Automated Remediation

Automated remediation involves automatically correcting configuration drift to maintain the desired state. This can be achieved using tools like AWS Config and AWS Systems Manager, which can automatically apply corrective actions when drift is detected.

Examples and Analogies

Example: Configuration Management

Using Ansible to ensure consistent configuration across multiple servers:

- hosts: webservers
  tasks:
    - name: Ensure Apache is installed
      yum:
        name: httpd
        state: present
    - name: Ensure Apache service is running
      service:
        name: httpd
        state: started
        enabled: yes
    

Example: Desired State Configuration (DSC)

Using AWS Systems Manager to define and maintain the desired state of an EC2 instance:

{
    "schemaVersion": "2.2",
    "description": "Ensure Apache is installed and running",
    "mainSteps": [
        {
            "action": "aws:runShellScript",
            "name": "installApache",
            "inputs": {
                "runCommand": [
                    "sudo yum install -y httpd",
                    "sudo systemctl start httpd",
                    "sudo systemctl enable httpd"
                ]
            }
        }
    ]
}
    

Example: Idempotency

Using Terraform to ensure an S3 bucket is created only if it does not exist:

resource "aws_s3_bucket" "example" {
  bucket = "my-unique-bucket-name"
  acl    = "private"
}
    

Example: Configuration Drift

Using AWS Config to detect and correct drift in security group configurations:

aws configservice put-config-rule --config-rule file://config-rule.json
    

Example: Automated Remediation

Using AWS Systems Manager to automatically remediate configuration drift:

{
    "schemaVersion": "1.2",
    "description": "Remediate configuration drift",
    "parameters": {},
    "mainSteps": [
        {
            "action": "aws:runCommand",
            "name": "remediateDrift",
            "inputs": {
                "DocumentName": "AWS-RunShellScript",
                "InstanceIds": ["i-1234567890abcdef0"],
                "Parameters": {
                    "commands": ["sudo yum install -y httpd"]
                }
            }
        }
    ]
}
    

Analogy: Building a House

Think of configuration management as building a house. Just as you would use blueprints and tools to ensure that each room is built according to plan, configuration management tools ensure that each system component is configured as intended. Configuration drift is like someone making changes to the house without updating the blueprints, leading to inconsistencies. Idempotency ensures that applying the same blueprint multiple times results in the same house layout.