Daily Hack #day73 - AWS CLI –dryrun flag

AWS CLI –dryrun Flag

The --dry-run flag in the AWS Command Line Interface (CLI) is a useful feature for testing commands without actually making any changes. It allows users to see the potential outcome of a command, ensuring that it will execute as expected before making any real modifications to their AWS resources.

Key Features:

1. Simulation: The --dry-run flag simulates the execution of an AWS CLI command, providing a preview of what the command will do without making any actual changes.

2. Validation: It helps validate the syntax and parameters of a command, catching errors and misconfigurations early.

3. Safety: By using --dry-run, users can safely test potentially destructive commands (such as deletions or modifications) to ensure they won't unintentionally affect critical resources.

Use Cases:

• Testing IAM Policies: Validate whether an IAM policy has the necessary permissions to perform an action without actually making changes.

    aws iam create-role --role-name MyTestRole --assume-role-policy-document file://policy.json --dry-run
  

• Verifying EC2 Actions: Check if an EC2 instance can be started or stopped without affecting the current state.

    aws ec2 start-instances --instance-ids i-1234567890abcdef0 --dry-run
  

• Cost Management: Preview the creation of resources (such as EC2 instances or RDS databases) to understand potential costs and configurations without incurring charges.

    aws ec2 run-instances --image-id ami-12345678 --count 1 --instance-type t2.micro --dry-run
  

Example Commands:

• EC2 Instance Start:

    aws ec2 start-instances --instance-ids i-1234567890abcdef0 --dry-run
  

  This command will simulate starting an EC2 instance and display whether the action is permitted.

• IAM Role Creation:

    aws iam create-role --role-name MyTestRole --assume-role-policy-document file://policy.json --dry-run
  

  This command will check if the IAM role can be created with the provided policy without actually creating it.

Benefits:

• Error Prevention: Helps catch errors and misconfigurations before they can cause issues in your environment.

• Confidence: Provides assurance that a command will execute as intended, reducing the risk of unintended changes.

• Efficiency: Saves time by allowing users to validate commands and configurations quickly and easily.

Limitations:

• Support: Not all AWS CLI commands support the --dry-run flag. It's typically used with commands that create, modify, or delete resources.

Using the --dry-run flag is a best practice when working with AWS CLI, especially for commands that have significant impact on your resources. It enhances the safety and reliability of your AWS operations by providing a straightforward way to validate commands before execution.