# Kubefile instruction

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 registry.cn-qingdao.aliyuncs.com/sealer-io/kubernetes:v1.19.8

# 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

# RUN instruction

The RUN instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Kubefile.

command format：RUN {command args ...}

USAGE：

For example ,Using RUN instruction to execute a commands that download kubernetes dashboard.

RUN wget https://raw.githubusercontent.com/kubernetes/dashboard/v2.2.0/aio/deploy/recommended.yaml

# CMD instruction

The format of CMD instruction is similar to RUN instruction, and also will execute any commands in a new layer. However, the CMD command will be executed when the cluster is started . it is generally used to start applications or configure the cluster. and it is different with Dockerfile CMD ,If you list more than one CMD in a Kubefile ,then all of them will take effect.

command format：CMD {command args ...}

USAGE：

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

CMD kubectl apply -f recommended.yaml