Frequently asked questions about Azure Container Instances

This article addresses frequently asked questions about Azure Container Instances.


How large can my container image be?

The maximum size for a deployable container image on Azure Container Instances is 15 GB. You might be able to deploy larger images depending on the exact availability at the moment you deploy, but this is not guaranteed.

The size of your container image impacts how long it takes to deploy, so generally you want to keep your container images as small as possible.

How can I speed up the deployment of my container?

Because one of the main determinants of deployment times is the image size, look for ways to reduce the size. Remove layers you don't need, or reduce the size of layers in the image (by picking a lighter base OS image). For example, if you're running Linux containers, consider using Alpine as your base image rather than a full Ubuntu Server. Similarly, for Windows containers, use a Nano Server base image if possible.

You should also check the list of pre-cached images in Azure Container Images, available via the List Cached Images API. You might be able to switch out an image layer for one of the pre-cached images.

See more detailed guidance on reducing container startup time.

What Windows base OS images are supported?


Due to issues with backward compatibility after the Windows updates in 2020, the following image versions include the minimum version number that we recommend you use in your base image. Current deployments using older image versions are not impacted, but new deployments should adhere to the following base images. After June 14th, 2021, ACI will no longer support deployments using older version numbers.

Windows Server 2016 base images


From now through 31 December 2022, you can continue to deploy Windows Server 2016 container groups on Azure Container Instances. After this date, Windows Server 2016 images will no longer be supported. See How do I migrate my Windows Server 2016 container groups to Windows Server 2019 images? for instructions on how to transition your workloads.


Windows images based on Semi-Annual Channel release 1709 or 1803 are not supported.

Windows Server 2019 and client base images

What .NET or .NET Core image layer should I use in my container?

Use the smallest image that satisfies your requirements. For Linux, you could use a runtime-alpine .NET Core image, which has been supported since the release of .NET Core 2.1. For Windows, if you are using the full .NET Framework, then you need to use a Windows Server Core image (runtime-only image, such as 4.7.2-windowsservercore-ltsc2016). Runtime-only images are smaller but do not support workloads that require the .NET SDK.


ACI cannot pull images from non OCI-compliant registries.

What types of container registries are compatible with ACI?

ACI supports image pulls from ACR and other third-party container registries such as DockerHub. ACI supports image pulls from ACR and other third-party OCI compatible container registries such as DockerHub with an endpoint that is publicly exposed to the internet.

How do I migrate my Windows Server 2016 container groups to Windows Server 2019 images?

  1. Identify what Windows base image you are currently using.

    If you're pulling directly from Microsoft Container Registry (MCR), then that image name is your base image.

    If you're working with a private registry, you'll need to look at your Dockerfile to identify the base image, which will be stated after the 'FROM' line.

  2. Select the new base image you want to use from Windows Server 2019. Below are some examples of commonly used Windows Server 2016 images on Azure Container Instances and our recommendations for replacement Windows Server 2019 images.

    Windows Server 2016 Image Recommended Windows Server 2019 Images

    Read about image discovery to learn more.


    If you would like assistance selecting your new base image, please create an Azure Support Ticket.

  3. Follow the Update containers in Azure Container Instances how-to guide to update your ACI container group to use your new base image.

    If you're using MCR for your container registry, you can pass the MCR image name directly into the container group image parameter.

    If you're using a private container registry, please follow the steps in Upgrade containers to a new version of the Windows operating system. Make sure the container group's image registry parameters are updated if you have changed them.

Availability and quotas

How many cores and memory should I allocate for my containers or the container group?

This really depends on your workload. Start small and test performance to see how your containers do. Monitor CPU and memory resource usage, and then add cores or memory based on the kind of processes that you deploy in the container.

Make sure also to check the resource availability for the region you are deploying in for the upper bounds on CPU cores and memory available per container group.


A small amount of a container group's resources is used by the service's underlying infrastructure. Your containers will be able to access most but not all of the resources allocated to the group. For this reason, plan a small resource buffer when requesting resources for containers in the group.

What underlying infrastructure does ACI run on?

Azure Container Instances aims to be a serverless containers-on-demand service, so we want you to be focused on developing your containers, and not worry about the infrastructure! For those that are curious or wanting to do comparisons on performance, ACI runs on sets of Azure VMs of various SKUs, primarily from the F and the D series. We expect this to change in the future as we continue to develop and optimize the service.

I want to deploy thousands of cores on ACI - can I get my quota increased?

Yes (sometimes). See the quotas and limits article for current quotas and which limits can be increased by request.

Can I deploy with more than 4 cores and 16 GB of RAM?

Not yet. Currently, these are the maximums for a container group. Contact Azure Support with specific requirements or requests.

When will ACI be in a specific region?

Current region availability is published here. If you have a requirement for a specific region, contact Azure Support.

Features and scenarios

How do I scale a container group?

Currently, scaling is not available for containers or container groups. If you need to run more instances, use our API to automate and create more requests for container group creation to the service.

What features are available to instances running in a custom VNet?

You can deploy container groups in an Azure virtual network of your choice, and delegate private IPs to the container groups to route traffic within the VNet across your Azure resources. For networking scenarios and limitations with Azure Container Instances, see Virtual network scenarios and resources.

Does the ACI service reserve ports for service functionality?

Yes, the ACI service does reserve the following ports for service functionality: 22, 443, 1025-1027, 3389-3399, 9999, 19000, 19080, 19390, 19100, 20000-30000, 49152-65534. Please avoid using these ports in your container group definition.


When does the meter start running?

Container group duration is calculated from the time that we start to pull your first container's image (for a new deployment) or your container group is restarted (if already deployed), until the container group is stopped. See details at Container Instances pricing.

Do I stop being charged when my containers are stopped?

Meters stop running once your entire container group is stopped. As long as a container in your container group is running, we hold the resources in case you want to start the containers up again.

Next steps