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Patching your Auto Scaling Group on AWS

In the fast-paced world of cloud computing, maintaining efficiency, security, and reliability is paramount. A key component in achieving these objectives is ensuring that server instances within Auto Scaling Groups (ASGs) are regularly updated and patched. This is where AWS Systems Manager Automation steps in, offering a streamlined, automated solution for managing these critical updates.

The Challenge: Keeping Auto Scaling Groups Up-to-Date

ASGs are essential for managing the scalability and availability of applications. They ensure that the number of instances adjusts automatically according to the defined conditions, such as traffic or load changes. However, regularly updating these instances, especially for patch management, can be a complex and time-consuming task. Manual interventions increase the risk of errors and inconsistencies, leading to potential security vulnerabilities and performance issues.

The Automated Solution

To address this challenge, a specialized AWS Systems Manager Automation document is used. This document automates the process of patching instances in an ASG, creating a new Amazon Machine Image (AMI) with the latest patches, and then updating the ASG to use this new AMI. This ensures that all new instances launched by the ASG will be up-to-date with the latest patches, thereby maintaining the security and stability of the environment.

How It Works

The automation process involves several key steps:

  1. Querying the ASG: The process starts by identifying the ASG that needs updating. This is done by querying ASGs based on specific tags, ensuring that the right group is targeted for the update.

  2. Creating a Patched Instance: A new EC2 instance is launched using the current AMI of the ASG. This instance is then used for patching.

  3. Patching and Image Creation: The newly launched instance undergoes a patching process based on the specified patch baseline. Post-patching, a new AMI is created from this instance. This step can be configured to either reboot or not reboot the instance after patching, depending on the user's choice.

  4. Updating the ASG: Once the new AMI is ready, the ASG's launch configuration is updated to use this new, patched AMI. This ensures that any new instances launched will be based on the updated AMI.

  5. Refreshing Instances: The final step involves refreshing the instances in the ASG. This means that existing instances are gradually replaced with new instances launched from the updated AMI, thus ensuring that all instances in the ASG are up-to-date.

  6. Monitoring and Verification: Throughout the process, checks and balances are in place to monitor the execution and ensure successful completion. This includes verifying the management state of the new instance and ensuring that the instance refresh in the ASG completes successfully.

Benefits of Automation

By automating the process of updating AMIs and ASGs, several benefits are realized:

  • Consistency and Reliability: Automation reduces the risk of human error and ensures that all instances are consistently patched and updated.
  • Security: Regular patching helps in addressing vulnerabilities quickly, enhancing the overall security posture.
  • Efficiency: Automating repetitive tasks like patching and AMI updates saves time and allows teams to focus on more strategic initiatives.
  • Scalability: As the infrastructure grows, this automated solution scales accordingly, handling updates without additional overhead.


In conclusion, leveraging AWS Systems Manager Automation for managing updates in Auto Scaling Groups offers a robust, efficient, and secure way to handle instance patching and AMI updates. This automated approach not only ensures that the infrastructure remains secure and up-to-date but also significantly reduces the operational burden on IT teams, allowing them to focus on more value-added activities.

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