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desktop: update c8d image store description
Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>
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David Karlsson
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This page provides information about the ongoing integration of `containerd` for
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image and file system management in the Docker Engine.
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## What is the containerd image store?
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## What is containerd?
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`containerd` is a container runtime that manages the container lifecycle, and
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provides image and filesystem management. It's a low-level building block,
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designed to be integrated into other systems, such as Docker and Kubernetes.
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`containerd` is an abstraction of the low-level kernel features
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used to run and manage containers on a system.
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It's a platform used in container software like Docker and Kubernetes.
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Docker Engine already uses `containerd` for container lifecycle management, which
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includes creating, starting, and stopping containers. This page describes the
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next step of containerd integration for Docker Engine: the image store.
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Docker Engine already uses `containerd` for container lifecycle management,
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which includes creating, starting, and stopping containers.
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This page describes the next step of the containerd integration for Docker:
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the containerd image store.
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The image store is the component responsible for pushing, pulling, and storing
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images. Integrating the containerd image store enables many new features in the
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Docker Engine, including:
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## Image store
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- containerd snapshotters, such as [stargz][1] for lazy-pulling images on startup,
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The image store is the component responsible for pushing, pulling,
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and storing images on the filesystem.
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The classic Docker image store is limited in the types of images that it supports.
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For example, it doesn't support image indices, containing manifest lists.
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When you create multi-platform images, for example,
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the image index resolves all the platform-specific variants of the image.
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An image index is also required when building images with attestations.
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The containerd image store extends range of image types
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that the Docker Engine can natively interact with.
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While this is a low-level architectural change,
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it's a prerequisite for unlocking a range of new use cases, including:
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- [Build multi-platform images](#build-multi-platform-images) and images with attestations
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- Support for using containerd snapshotters with unique characteristics,
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such as [stargz][1] for lazy-pulling images on container startup,
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or [nydus][2] and [dragonfly][3] for peer-to-peer image distribution.
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- Natively store and build multi-platform images, and other OCI content types
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that may emerge in the future.
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- Ability to run [Wasm](wasm.md) containers
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[1]: https://github.com/containerd/stargz-snapshotter
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[2]: https://github.com/containerd/nydus-snapshotter
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[3]: https://github.com/dragonflyoss/image-service
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The image store integration is still at an early stage, so not all features are
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yet supported.
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## Enable the containerd image store
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## Turn on the containerd image store feature
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After switching to the containerd image store,
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images and containers in the classic image store won't be visible.
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All of those containers and images still exist.
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To see them again, turn off the containerd image store feature.
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The containerd image store isn't turned on by default. To start using the
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feature:
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The containerd image store isn't enabled by default.
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To enable the feature for Docker Desktop:
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1. Navigate to **Settings**.
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1. Navigate to **Settings** in Docker Desktop.
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2. In the **General** tab, check **Use containerd for pulling and storing images**.
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3. Select **Apply & Restart**
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3. Select **Apply & Restart**.
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To turn off this feature, clear the **Use containerd for pulling and storing
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images** checkbox.
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To disable the containerd image store,
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clear the **Use containerd for pulling and storing images** checkbox.
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> **Tip**
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>
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> After switching to the containerd image store, images and containers from the
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> default image store won't be visible. All of those containers and images
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> still exist. To see them again, turn off the containerd image store feature.
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{ .tip }
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## Build multi-platform images
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## Building multi-platform images
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The term multi-platform image refers to a bundle of images that can run on different architectures.
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The term multi-platform image refers to a bundle of images for multiple different architectures.
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Out of the box, the default builder for Docker Desktop doesn't support building multi-platform images.
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```console
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$ docker buildx ls | grep "DRIVER\|*"
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NAME/NODE DRIVER/ENDPOINT STATUS BUILDKIT PLATFORMS
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default * docker
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$ docker buildx build --platform=linux/amd64,linux/arm64 .
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$ docker build --platform=linux/amd64,linux/arm64 .
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[+] Building 0.0s (0/0)
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ERROR: multiple platforms feature is currently not supported for docker driver. Please switch to a different driver (eg. "docker buildx create --use")
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ERROR: Multi-platform build is not supported for the docker driver.
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Switch to a different driver, or turn on the containerd image store, and try again.
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Learn more at https://docs.docker.com/go/build-multi-platform/
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```
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Normally, building multi-platform images requires you to create a new builder,
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using a driver that supports multi-platform builds.
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But even then, you can't load the multi-platform images to your local image store.
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Enabling the containerd image store lets you build multi-platform images
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and load them to your local image store:
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```console
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$ docker buildx create --bootstrap
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[+] Building 2.4s (1/1) FINISHED
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=> [internal] booting buildkit
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=> => pulling image moby/buildkit:buildx-stable-1
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=> => creating container buildx_buildkit_objective_blackburn0
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objective_blackburn
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$ docker buildx build --quiet \
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--platform=linux/amd64,linux/arm64 \
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--builder=objective_blackburn \
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--load .
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ERROR: docker exporter does not currently support exporting manifest lists
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```
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Turning on the containerd image store lets you build, and load, multi-platform images
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to your local image store, all while using the default builder.
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```console
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$ docker info --format="{{ .Driver }}"
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stargz
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$ docker buildx build \
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--platform=linux/arm64,linux/amd64 \
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--tag=user/containerd-multiplatform .
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[+] Building 6.2s (11/11) FINISHED
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...
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=> [internal] load build definition from Dockerfile 0.0s
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=> => transferring dockerfile: 115B 0.0s
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=> [linux/arm64 internal] load metadata for docker.io/library/alpine:latest 2.0s
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=> [linux/amd64 internal] load metadata for docker.io/library/alpine:latest 2.1s
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=> [linux/amd64 1/1] FROM docker.io/library/alpine@sha256:124c7d2707904e... 0.0s
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=> => resolve docker.io/library/alpine@sha256:124c7d2707904eea7431fffe91... 0.0s
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=> [linux/arm64 1/1] FROM docker.io/library/alpine@sha256:124c7d2707904e... 0.0s
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=> => resolve docker.io/library/alpine@sha256:124c7d2707904eea7431fffe91... 0.0s
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=> exporting to image 0.0s
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=> => exporting layers 0.0s
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...
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=> => naming to docker.io/user/containerd-multiplatform:latest 0.0s
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=> => unpacking to docker.io/user/containerd-multiplatform:latest 0.0s
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$ docker images
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REPOSITORY TAG IMAGE ID CREATED SIZE
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user/containerd-multiplatform latest 7401bb14c229 14 seconds ago 3.38MB
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user/containerd-multiplatform latest 7401bb14c229 14 seconds ago 3.26MB
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```
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You can push the multi-platform image to Docker Hub.
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```console
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$ docker push user/containerd-multiplatform
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Using default tag: latest
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699c4e744ab4: Pushed
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878d877e4f70: Pushed
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f56be85fc22e: Pushed
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a579f49700dc: Pushed
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c41833b44d91: Pushed
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ee79e74f9211: Pushed
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d28bdb47b683: Pushed
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```
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Inspecting the tag on Docker Hub shows that the image is available for multiple platforms.
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## Known issues
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### Docker Desktop 4.13.0 release
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- Listing images with `docker images` returns the error
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`content digest not found` on ARM machines after running or pulling an image
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with the `--platform` parameter.
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### Docker Desktop 4.12.0 release
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- The containerd image store feature requires Buildx version 0.9.0 or newer.
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- On Docker Desktop for Linux (DD4L), validate if your locally installed
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version meets this requirement.
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> **Note**
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>
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> If you're using an older version, the Docker daemon reports the following
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> error:
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> `Multiple platforms feature is currently not supported for docker driver.`
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> `Please switch to a different driver`.
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>
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> Install a newer version of Buildx following the instructions on
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> [how to manually download Buildx](../../build/architecture.md#install-buildx).
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- In Docker Desktop 4.12.0, the containerd image store feature is incompatible
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with the Kubernetes cluster support. Turn off the containerd image store
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feature if you are using the Kubernetes from Docker Desktop.
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- Local registry mirror configuration isn't implemented yet with the containerd
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image store. The `registry-mirrors` and `insecure-registries` aren't taken
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into account by the Docker daemon.
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- The `reference` filter isn't implemented yet and will return the error
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`invalid filter 'reference'` when listing images.
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- Pulling an image may fail with the error
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`pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed`,
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in the situation where the image does not contain a manifest list. To
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workaround this issue run the `docker login` command and pull the image again.
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<script async id="asciicast-ZSUI4Mi2foChLjbevl2dxt5GD" src="https://asciinema.org/a/ZSUI4Mi2foChLjbevl2dxt5GD.js"></script>
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## Feedback
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