hostconfig-operator/docs/Overview.md

HostConfig Operator

Overview

An ansible based operator to perform host configuration LCM operations on Kubernetes Nodes. It is built to execute the required configuration on kubernetes nodes after the intial kubernetes setup is done on the nodes. The application is deployed as a pod on the existing cluster itself.

Current implementation have been tested with running three replicas of the hostconfig operator deployment launched on different master nodes in the kubernetes setup.

Once the hostconfig operator is deployed and the corresponding CRD is created on the kubernetes cluster, we can then create the HostConfig CR objects to perform the required configuration on the nodes.

The host configuration on the kubernetes nodes is done by executing the appropriate ansible playbook on that Kubernetes node by the hostconfig operator pod.

Scope and Features

• Perform host configuration LCM operations on Kubernetes hosts
• LCM operations managed using HostConfig CR objects
• Inventory built dynamically, at the time of playbook execution
• Connects to hosts using the secrets associated with the nodes, which have the ssh keys associated in them.
• Supports execution based on host-groups, which are built based out of labels associated with kubernetes nodes
• Supports serial/parallel execution of configuration on hosts
• Supports host selection with AND and OR operations of the labels mentioned in the host-groups of the CR object
• Reconcile on failed nodes, based on reconcile period - feature available from ansible-operator
• Current support is available to perform sysctl and ulimit operations on the kubernetes nodes.
• Any shell command that needs to be executed on the nodes can use the exec config option.
• Display the status of each Hostconfig CR object as part of the kubectl describe hostconfig <name>
• We have also added an anisble role to execute the "kubeadm alpha cert check-expiration" command and annotate the nodes with expiration detail.
• Added support to upgrade packages and restart the corresponding services Current implementation supports installing/upgrading docker, containerd and apache2. It also supports installing python3-openstackclient and python3-novaclient binaries.
• Added support to apply custom apparmor profiles to kubernetes nodes

Architecture

Hostconfig operator will be running as a kubernetes deployment on the target kubernetes cluster.

This repository also have vagrants scripts to build kubernetes cluster on the Vagrant VMs and has to deploy and configure the hostconfig-operator pod on the K8 setup.

Deployment and Host Configuration Flow

The hostconfig operator deployment sequence

Using operator pod to perform host configuration on kubernetes nodes

How to Deploy(On existing kubernetes cluster)

Pre-requisite:

1. The Kubernetes nodes should be labelled with any one of the below label to execute based on host-groups, if not labelled by default executes on all the nodes as no selection happens. Valid labels:

   • topology.kubernetes.io/region
   • topology.kubernetes.io/zone
   • kubernetes.io/role
   • kubernetes.io/hostname
   • kubernetes.io/arch
   • kubernetes.io/os

2. Operator pod connecting to Kubernetes Nodes:

   The kubernetes nodes should be annotated with secret name having the username and private key as part of the contents.

   git clone the hostconfig repository

   git clone https://opendev.org/airship/hostconfig-operator.git

   Move to airship-host-config directory

   cd hostconfig-operator/airship-host-config

   Create a HostConfig CRD

   kubectl create -f deploy/crds/hostconfig.airshipit.org_hostconfigs_crd.yaml

   Create hostconfig role, service account, role-binding and cluster-role-binding which is used to deploy and manage the operations done using the hostconfig operator pod

   kubectl create -f deploy/role.yaml kubectl create -f deploy/service_account.yaml kubectl create -f deploy/role_binding.yaml kubectl create -f deploy/cluster_role_binding.yaml

   Now deploy the hostconfig operator pod

   kubectl create -f deploy/operator.yaml

   Once the hostconfig operator pod is deployed, we can create the desired HostConfig CR with the required configuration. And this CR is passed to the operator pod which performs the required operation.

   Some example CRs are available in the demo_examples directory.

   Please refer to README.md file for more detailed steps.

References

1. https://docs.openshift.com/container-platform/4.1/applications/operator_sdk/osdk-ansible.html
2. https://github.com/operator-framework/operator-sdk
3. https://docs.ansible.com/ansible/latest/modules/sysctl_module.html
4. https://docs.ansible.com/ansible/latest/modules/pam_limits_module.html