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 witch 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 then into CloudImage
Cloud Builder, sealer will create a Cluster using public cloud, and exec RUN & CMD command witch 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 installl cluster.
Config : application config, like mysql username passwd or other configs, you can using 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 helth or not, found reason when things unexpected.

Other modules

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