Final answer:
Without the CodeDeploy agent installed on instances in an autoscaling group, AWS CodeDeploy cannot deploy applications properly, resulting in a failed deployment process. The agent must be included in the instance initialization for successful deployment.
Step-by-step explanation:
If the CodeDeploy agent is not installed on instances when deploying with autoscaling, the deployment process will fail. AWS CodeDeploy is a deployment service that enables developers to automate the deployment of applications to instances across various computing environments, including those set up with autoscaling. The CodeDeploy agent is essential for the instances in the autoscaling group to communicate with the service, pull application revisions, and perform the deployment tasks.
Without the agent, the autoscaling group’s instances will not be able to properly execute the deployment instructions, and as such, the application may not be rolled out correctly across the new instances. Typically, you'll need to incorporate the agent installation into the instance startup process, such as using a launch configuration script or a base AMI that includes the agent. If deployment fails due to a missing CodeDeploy agent, it is crucial to ensure that all future instances launched by the autoscaling group contain the agent, either by updating the AMI or the initialization script used by the autoscaling group.