When deploying an Azure Container Instance (ACI) using an image from an Azure Container Registry (ACR), the deployment must authenticate to the registry to pull the image. By default, ACR is secured, and you cannot pull images anonymously unless they are public.
According to the Azure Administrator study guide, enabling the Admin user option in ACR generates two access credentials (username and password) that can be used for authentication when pulling container images. When the Admin user setting is disabled, you cannot authenticate directly using those credentials, and automated deployments may fail with authentication errors.
By enabling the Admin user setting, Azure creates a service-level user account for the registry with permissions to push and pull images. These credentials can then be referenced securely in your container instance configuration - either through the Azure portal, ARM template, or CLI parameters such as -- registry-username and --registry-password.
This configuration allows ACI to authenticate successfully against the ACR and pull the required image (image1) for deployment.
Therefore, enabling the Admin user for the container registry meets the goal of allowing the deployment of the container instance using image1.