LCM controller

LCM controller runs on the management and regional cluster and orchestrates the LCMMachine objects according to their type and their LCMCluster object.

Once the LCMCluster and LCMMachine objects are created, LCM controller starts monitoring them to modify the spec fields and update the status fields of the LCMMachine objects when required. The status field of LCMMachine is updated by LCM agent running on a node of a management, regional, or managed cluster.

Each LCMMachine has the following lifecycle states:

  1. Uninitialized - the machine is not yet assigned to an LCMCluster.

  2. Pending - the agent reports a node IP address and hostname.

  3. Prepare - the machine executes StateItems that correspond to the prepare phase. This phase usually involves downloading the necessary archives and packages.

  4. Deploy - the machine executes StateItems that correspond to the deploy phase that is becoming a Mirantis Kubernetes Engine (MKE) node.

  5. Ready - the machine is being deployed.

  6. Upgrade - the machine is being upgraded to the new MKE version.

  7. Reconfigure - the machine is being updated with a new set of manager nodes. Once done, the machine moves to the ready state again.

The templates for StateItems are stored in the machineTypes field of an LCMCluster object, with separate lists for the MKE manager and worker nodes. Each StateItem has the execution phase field for a management, regional, and managed cluster:

  1. The prepare phase is executed for all machines for which it was not executed yet. This phase comprises downloading the files necessary for the cluster deployment, installing the required packages, and so on.

  2. During the deploy phase, a node is added to the cluster. LCM controller applies the deploy phase to the nodes in the following order:

    1. First manager node is deployed.

    2. The remaining manager nodes are deployed one by one and the worker nodes are deployed in batches (by default, up to 50 worker nodes at the same time). After at least one manager and one worker node are in the ready state, helm-controller is installed on the cluster.

LCM controller deploys and upgrades a Mirantis Container Cloud cluster by setting StateItems of LCMMachine objects following the corresponding StateItems phases described above. The Container Cloud cluster upgrade process follows the same logic that is used for a new deployment, that is applying a new set of StateItems to the LCMMachines after updating the LCMCluster object. But during the upgrade, the following additional actions are performed:

  • If the existing worker node is being upgraded, LCM controller performs draining and cordoning on this node honoring the Pod Disruption Budgets. This operation prevents unexpected disruptions of the workloads.

  • LCM controller verifies that the required version of helm-controller is installed.