images

Xcluster overlay - images

Handles images in xcluster. Holds help script for docker images, local registry and pre-pulled images.

The script for private registry is the most usable. Check the help printouts:

images    # Help printout
# Cache images used by an ovl in the private registry if needed
images lreg_preload k8s-cni-calico

Build local images

An directory with a working ./tar file and a Dockerfile can be used to create a local image. A temporary docker "context" directory is created. The ./tar file is used to produce a ovl.tar in that context which should be used. Here is an example from ovl/metallb;

FROM scratch
ADD --chown=0:0 ovl.tar /
CMD ["/bin/controller"]

The image can then be build with the "images mkimage" command;

images mkimage --force --tag=library/metallb:latest --upload ./image

OBSOLETE: Pre-pulled images

Pre-pulled images as an ovl is very hard to maintain and requires sudo. It is recommended to use a private registry instead.

To install pre-pulled images on the xcluster disk image or as an overlay saves time since nothing has to be dowloaded. In some environments it is also hard to get external connectivity inside the VMs.

What we want to do is to create an overlay with the containers-storage structure containing all images we need. This is not so simple and it requires "sudo", at least for now.

The way this is done at the moment is;

• Pull or import the image to you local docker-daemon. You should see it with docker images.

• Use skopeo to copy all pre-pulled images to a containers-storage on /tmp/var. This requires sudo.

• Tar the /tmp/var structure. This also requires sudo since skopeo protects the dir.

• Use the tar-file as an xcluster overlay.

Preparations

cd $($XCLUSTER ovld images)
sudo mkdir /etc/containers
sudo cp policy.json storage.conf /etc/containers

Usage

An image overlay is created with the images.sh script. By default it is created in the $XCLUSTER_TMP directory. The items may be;

• A docker image reference. The version must be included.
• An overlay dir. The image/ dir in the overlay will be used.
• An overlay dir and subdir, like proxy/image2

# ("images" alias defined in $h/Envsettings)
# Requires "sudo"
images make k8s.gcr.io/pause:3.6 \
  registry.nordix.org/cloud-native/mconnect:latest docker.io/library/alpine:latest
eval $($XCLUSTER env | grep XCLUSTER_TMP)
ls $XCLUSTER_TMP/images.tar
xc mkcdrom [overlays...] images

You will be prompted for password.

You may notice that the xc mkcdrom can take just images as parameter? The secret is in the tar script in the images ovl dir.

Check images on a VM

On the VMs an alias will be set to list the pre-pulled images;

alias images="crictl --runtime-endpoint=unix:///var/run/crio/crio.sock images"