sealer

# Kubefile

A Kubefile is a text document that contains all the commands a user could call on the command line to assemble an image.We can use the Kubefile to define a cluster image that can be shared and deployed offline. a Kubefile just like Dockerfile which contains the build instructions to define the specific cluster.

# FROM instruction

The FROM instruction defines which base image you want reference, and the first instruction in Kubefile must be the FROM instruction. Registry authentication information is required if the base image is a private image. By the way official base images are available from the Sealer community.

command format：FROM {your base image name}

USAGE：

For example ,use the base image kubernetes:v1.19.8 which provided by the Sealer community to build a new cloud image.

FROM docker.io/sealerio/kubernetes:v1.22.15

# COPY instruction

The COPY instruction used to copy the contents from the context path such as file or directory to the rootfs, and the default src path is the rootfs .If the specified destination directory does not exist, sealer will create it automatically.

command format：COPY {src dest}

USAGE：

For example , copy mysql.yamltorootfs/mysql.yaml

COPY mysql.yaml .

For example , copy directory apollo to rootfs/charts/apollo

COPY apollo charts

# CMDS instruction

NOTE: LAUNCH instruction is more recommended than CMDS.

The format of CMDS instruction will execute any commands in a new layer. The CMDS command will be executed when sealer run . It is generally used to start applications or configure the cluster.

And there are some points that require special attention:

  • Just like with Dockerfile CMD , if there are multiple CMDS instructions in the Kubefile, only the last one takes effect.
  • The CMDS of the parent image will not be inherited, and you need to redefine it in the child image if you need to have it set.
  • The CMDS instruction and the LAUNCH instruction are in conflict, and only one of them can exist.

command format：CMD {command args ...}

USAGE：

For example ,Using CMDS instruction to execute a commands that apply the kubernetes dashboard yaml.

CMDS ["kubectl apply -f recommended.yaml","echo success"]

# APP instruction

The APP instruction defines an app virtual object and specify the materials that needed to start an app, and finally we can define the running object in terms of the dimensions of the APP by LAUNCH instruction. For now, you can specify the type of material included:

  • Helm Chart
  • K8S YAML
  • Linux Shell

command format：APP {command args ...}

USAGE：

For example:

  • Using APP instruction to define a mysql app and it will use local chart dir local://mysql/ to start it.

    APP mysql local://mysql/

  • Using APP instruction to define a dashboard app and it will use remote k8s resource file to start it and the remote file will be auto downloaded.

    APP dashboard https://raw.githubusercontent.com/kubernetes/dashboard/v2.7.0/aio/deploy/recommended.yaml

  • Using APP instruction to define a dashboard app and it will use local k8s resource file recommended.yaml to start it.

    APP dashboard local://recommended.yaml

  • Using APP instruction to define a business app and it will use local shell file install.sh to start it.

    APP business local://install.sh

# LAUNCH instruction

The LAUNCH instruction specifies a list of apps to launch when sealer run. Only one LAUNCH instruction can be defined in the Kubefile.

And there are some points that require special attention:

  • The LAUNCH of the parent image will not be inherited, and you need to redefine it in the child image if you need to have it set.
  • The LAUNCH instruction and the CMDS instruction are in conflict, and only one of them can exist.

command format：LAUNCH {command args ...}

USAGE：

For example ,Using LAUNCH instruction to start mysql and business apps defined by APP instruction.

LAUNCH ["mysql","business"]

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