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 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 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.