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Building Cluster Images Based on go-template

During the process of building cluster images, we can use the --env option to pass some variables through the sealos command line. These environment variables can be used by the CMD command of the Kubefile or the yaml file template.

Using Environment Variables in Kubefile​

This example defines a SERVICE_TYPE variable that allows the user to customize the service exposure type when installing the application and pass parameters to the helm command in CMD.

Kubefile example:

FROM scratch
ENV SERVICE_TYPE "NodePort"
COPY charts charts
COPY registry registry
CMD ["helm upgrade --install nginx charts/nginx --namespace=nginx --create-namespace --set service.type=$(SERVICE_TYPE)"]

Run the cluster application and set a custom SERVICE_TYPE=LoadBalancer, if not set, it will default to NodePort.

sealos run labring/nginx:v1.23.1 --env SERVICE_TYPE=LoadBalancer

Using Environment Variables in Yaml Files​

Prepare a simple nginx service yaml file, this file must be a *.tmpl extension to be rendered when running sealos run --env command.

$ cat manifests/service.yaml.tmpl
apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    name: nginx
spec:
  type: {{ .serviceType }}
  ports:
    - port: 80
      nodePort: {{ .http_NodePort }}
      name: http
    - port: 443
      nodePort: {{ .https_NodePort }}
      name: https
  selector:
    name: nginx

Here is a Kubefile example where you can set the default environment variables.

FROM scratch
ENV serviceType NodePort
ENV http_NodePort 30080
ENV https_NodePort 30443

COPY manifests manifests
COPY registry registry
CMD ["kubectl apply -f manifests/service.yaml"]

When you build the image, nothing will happen, it only renders when running the application. If --env is not set, it will use the default ENV in Kubefile.

sealos run labring/nginx:1.23.1 --env serviceType=LoadBalancer --env http_NodePort=30080 --env https_NodePort=30443

You will find that sealos renders a new yaml file service.yaml based on service.yaml.tmpl on the local path of the master node.

Note The new version of the application's rootfs is placed in the /var/lib/sealos/data/default/applications directory, each application has its independent directory.

root@node1:~# ls /var/lib/sealos/data/default/rootfs/manifests |grep service
service.yaml
service.yaml.tmpl

Check the yaml content:

root@node1:~# cat /var/lib/sealos/data/default/rootfs/manifests/service.yaml
apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    name: nginx
spec:
  type: NodePort
  ports:
    - port: 80
      nodePort: 30080
      name: http
    - port: 443
      nodePort: 30443
      name: https
  selector:
    name: nginx

Note: All types of files support this feature (the file name suffix is .tmpl and the build directory is in etc, scripts, and manifests), you can try it yourself.