What is CloudRootfs

All the files witch run a kubernetes cluster needs.

Contains:

  • Bin files, like docker containerd crictl kubeadm kubectl…
  • Config files, like kubelet systemd config, docker systemd config, docker daemon.json…
  • Registry docker image
  • Some Metadata, like Kubernetes version.
  • Registry files, contains all the docker image, like kubernetes core component docker images…
  • Scripts, some shell script using to install docker and kubelet… sealer will call init.sh and clean.sh.
  • Other static files
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.
├── bin
│   ├── conntrack
│   ├── containerd-rootless-setuptool.sh
│   ├── containerd-rootless.sh
│   ├── crictl
│   ├── kubeadm
│   ├── kubectl
│   ├── kubelet
│   ├── nerdctl
│   └── seautil
├── cri
│   ├── containerd
│   ├── containerd-shim
│   ├── containerd-shim-runc-v2
│   ├── ctr
│   ├── docker
│   ├── dockerd
│   ├── docker-init
│   ├── docker-proxy
│   ├── rootlesskit
│   ├── rootlesskit-docker-proxy
│   ├── runc
│   └── vpnkit
├── etc
│   ├── 10-kubeadm.conf
│   ├── Clusterfile  # image default Clusterfile
│   ├── daemon.json
│   ├── docker.service
│   ├── kubeadm-config.yaml
│   └── kubelet.service
├── images
│   └── registry.tar  # registry docker image, will load this image and run a local registry in cluster
├── Kubefile
├── Metadata
├── README.md
├── registry # will mount this dir to local registry
│   └── docker
│       └── registry
├── scripts
│   ├── clean.sh
│   ├── docker.sh
│   ├── init-kube.sh
│   ├── init-registry.sh
│   ├── init.sh
│   └── kubelet-pre-start.sh
└── statics # yaml files, sealer will render values in those files
    └── audit-policy.yml

How can I get CloudRootfs

  1. Pull a BaseImage sealer pull kubernetes:v1.19.8-alpine
  2. View the image layer information sealer inspect kubernetes:v1.19.8-alpine
  3. Get into the BaseImage Layer ls /var/lib/sealer/data/overlay2/{layer-id}

You will found the CloudRootfs layer.

Build your own BaseImage

You can edit any files in CloudRootfs you want, for example you want to define your own docker daemon.json, just edit it and build a new CloudImage.

script
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FROM scratch
COPY . .
script
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sealer build -t user-defined-kubernetes:v1.19.8 .

Then you can use this image as a BaseImage.

OverWrite CloudRootfs files

Sometimes you don’t want to care about the CloudRootfs context, but need custom some config.

You can use kubernetes:v1.19.8 as BaseImage, and use your own config file to overwrite the default file in CloudRootfs.

For example: daemon.json is your docker engine config, using it to overwrite default config:

script
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FROM kubernetes:v1.19.8
COPY daemon.json etc/
script
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sealer build -t user-defined-kubernetes:v1.19.8 .