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Customize a Cluster by Build image

This guide explains how to customize a Kubernetes cluster by building a custom image using kubeadm config.

Building a Customize Image​

To build a custom image, run the following command:

$ mkdir -p /tmp/buildimage
  cat > /tmp/buildimage/kubeadm.yml <<EOF
  apiVersion: kubeadm.k8s.io/v1beta2
  kind: ClusterConfiguration
  networking:
    serviceSubnet: "100.55.0.0/16"
    podSubnet: "10.160.0.0/12"
EOF

$ cat > /tmp/buildimage/Kubefile <<EOF
  FROM labring/kubernetes-docker:v1.25.0
  COPY kubeadm.yml etc/
EOF

$ sudo sealos build --debug -t hack:dev  /tmp/buildimage

In this example, we create a directory /tmp/buildimage and create a kubeadm.yml file inside it that specifies the desired configuration for the image. We then create a Kubefile that specifies the base image and copies the kubeadm.yml file into the image. We use sealos build to build an image named hack:dev from the contents of the /tmp/buildimage directory.

Appending an Application Configuration to Clusterfile​

Next, we will append an application configuration to Clusterfile. For example, if you want to change the CIDR range of pods, you should change the spec.data.spec.calicoNetwork.ipPools.cidr fields. The final Clusterfile will be like this:

apiVersion: apps.sealos.io/v1beta1
kind: Cluster
metadata:
  name: default
spec:
  hosts:
    - ips:
        - 192.168.0.2:22
        - 192.168.0.3:22
        - 192.168.0.4:22
      roles:
        - master
        - amd64
    - ips:
        - 192.168.0.5:22
        - 192.168.0.6:22
        - 192.168.0.7:22
      roles:
        - node
        - amd64
  image:
    - hack:dev
    - labring/helm:v3.8.2
    - labring/calico:v3.24.1
  ssh:
    passwd: xxx
    pk: /root/.ssh/id_rsa
    port: 22
    user: root
status: {}
---
apiVersion: apps.sealos.io/v1beta1
kind: Config
metadata:
  name: calico
spec:
  path: charts/calico/values.yaml
  strategy: merge
  data: |
    installation:
      enabled: true
      kubernetesProvider: ""
      calicoNetwork:
        ipPools:
        - blockSize: 26
          cidr: 10.160.0.0/12
          encapsulation: IPIP
          natOutgoing: Enabled
          nodeSelector: all()
        nodeAddressAutodetectionV4:
          interface: "eth.*|en.*"

In this example, we have appended a configuration for the calico application to Clusterfile. This configuration specifies the CIDR range of pods and other options necessary for the application to run.

Installing the Cluster​

Finally, we can use sealos apply -f Clusterfile to install the cluster. After the cluster is installed, Clusterfile will be saved in the .sealos/default/Clusterfile directory. You can modify the Clusterfile to customize the cluster further.

⚠️ Notes:

  • You can refer to the official docs or use the kubeadm config print init-defaults command to print kubeadm configuration.
  • For experimental usage, see the CLI documentation.