Implementing up-to-date images with automated EC2 Image Builder pipelines
This blog post is written by Devin Gordon, Senior Solutions Architect, WWPS, and Brad Watson, Senior Solutions Architect, WWPS.
Amazon EC2 Image Builder is a service designed to simplify the creation and deployment of customized Virtual Machine (VM) and container images on AWS or on-premises. The posts Automate OS Image Build Pipelines with EC2 Image Builder and Quickly build STIG-compliant Amazon Machine Images using Amazon EC2 Image Builder show how you can create secure images using EC2 Image Builder pipelines.
In this post, we demonstrate how to automatically keep your base or standard images current, incorporating patches and any other changes using EC2 Image Builder pipelines. We also demonstrate how to keep workload-specific images current using Cascading Pipelines, a feature of EC2 Image Builder.
You can use the Dependency update feature of EC2 Image Builder pipelines to automatically update your standard image based on changes to your build components.
When you create an EC2 Image Builder pipeline, you can choose to run the pipeline on a schedule, either using a schedule builder or a CRON expression (a method of defining minute, hour, day and month for scheduling). Furthermore, you can choose to only run the pipeline if a component in the pipeline or the source image has changed. This is referred to as a dependency update as shown in the following image.
Figure 1: An example EC2 Image Builder pipeline schedule with dependency update settings
When you select “Run pipeline at the scheduled time if there are dependency updates,” your pipeline only executes if the Base AMI or any Build or Test components have changed. The version of your components must be updated for this capability to work. Amazon-provided components include versioning out of the box. Here is an example of three versions of an Amazon-provided Build component that apply Security Technical Implementation Guide (STIG) baselines to Linux images.
Figure 2: Different versions of one Amazon-managed Build component
When a new STIG baseline build component is released, the component’s version is incremented. If a pipeline includes this type of versioned Build component and utilizes the dependency updates capability, then the pipeline automatically runs at the next scheduled interval after the component is updated. Pipelines utilizing this capability will run when the base AMI changes or when a Build or Test component changes.
To receive notifications about the pipeline execution, you can enable an Amazon Simple Notification Service (Amazon SNS) topic from within EC2 Image Builder. Under the Infrastructure Configuration section of the EC2 Image Builder pipeline, identify an SNS topic as shown in the following image.
Figure 3: An example SNS topic for sending pipeline execution notifications
The SNS topic receives a notification if a pipeline runs and completes with a status of AVAILABLE or FAILED. This occurs even when a pipeline execution is triggered by a component change that you didn’t directly initiate, such as when a new version of an Amazon-managed build component is released.
Even if no other aspects of the infrastructure configuration are used in the pipeline (instance type, security group, subnet, etc.), the SNS topic capability can be used to send a notification when the pipeline executes. With this in mind, you can leverage Amazon SNS to make sure that you’re always notified of any pipeline executions as well as trigger AWS Lambda functions for automation.
Cascading Pipelines are a feature of EC2 Image Builder that you can use to create workload-specific images from a standard secured image (aka “gold image”) of an organization. The following image shows how you can use Cascading Pipelines to keep workload specific images updated.
Figure 4: An example workflow for a EC2 Image Builder Cascading Pipelines
You create a gold image pipeline for a hardened base operating system (OS) using the steps outlined in Automate OS Image Build Pipelines with EC2 Image Builder. This pipeline could include a base OS, OS patches, Build components to harden the OS (such as STIG or CIS baselines), as well as any additional software required by the organization (agents, etc.). Do not include application- or workload-specific software in the pipeline. Infrastructure or distribution components may not be included in the pipeline to maintain flexibility for using the gold image. For example, you typically wouldn’t want to include VPC configurations in your golden AMI build because that would constrain the AMI to a particular VPC.
To create a Cascading Pipeline that uses the gold image for applications or workloads, in the Base Image section of the EC2 Image Builder console, choose Select Managed Images.
Figure 5: Selecting the base image of a pipeline
Then, select “Images Owned by Me” and under Image Name, select the EC2 Image Builder pipeline used to create the gold image. Moreover, select “Use Latest Available OS Version” under Auto-versioning options to make sure that the Cascading Pipeline is executed any time there is a change to the base image.
Figure 6: Choosing the base golden image from a previous pipeline execution
Use this configuration to maintain images for each application or workload which utilizes the gold image. Any time that an update is made to the gold image, application pipelines execute, thus providing updated images. To send notifications, SNS topics are enabled on each workload-specific pipeline.
In this post, we demonstrated how to automatically update images for any changes using EC2 Image Builder pipelines. We also demonstrated how to keep workload specific images using Cascading Pipelines. Using these features, you can make sure that your organization stays up-to-date on the latest OS patches and dependency changes, without requiring human intervention. For more information on EC2 Image Builder, see the official documentation.