# Architecture

Sealer has two top module: Build Engine & Apply Engine

The Build Engine Using Kubefile and build context as input, and build a CloudImage that contains all the dependencies. The Apply Engine Using Clusterfile to init a cluster which contains kubernetes and other applications.

# Build Engine

• Parser : parse Kubefile into image metadata
• Registry : push or pull the CloudImage
• Store : save CloudImage to local disks

# Builders

• Lite Builder, sealer will check all the manifest or helm chart, decode docker images in those files, and cache them into CloudImage.
• Cloud Builder, sealer will create a Cluster using public cloud, and exec RUN & CMD command which defined in Kubefile, then cache all the docker image in the Cluster.
• Container Builder, Using Docker container as a node, run kubernetes cluster in container then cache all the docker images.

# Apply Engine

• Infra : manage infrastructure, like create VMs in public cloud then apply the cluster on top of it. Or using docker emulation nodes.
• Runtime : cluster installer implementation, like using kubeadm to install cluster.
• Config : application config, like mysql username passwd or other configs, you can use Config overwrite any file you want.
• Plugin : plugin help us do some extra work, like exec a shell command before install, or add a label to a node after install.
• Debug : help us check the cluster is healthy or not, find reason when things unexpected.

# Other modules

• Filesystem : Copy CloudRootfs files to all nodes
• Mount : mount CloudImage all layers together
• Checker : do some pre-check and post check
• Command : a command proxy to do some tasks which os don't have the command. Like ipvs or cert manager.
• Guest : manage user application layer, like exec CMD command defined in Kubefile.