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06-Kube-Controller-Manager.md

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Kube Controller Manager

In this section, we will take a look at kube-controller-manager.

Kube Controller Manager manages various controllers in kubernetes.

  • In kubernetes terms, a controller is a process that continously monitors the state of the components within the system and works towards bringing the whole system to the desired functioning state.

Node Controller

  • Responsible for monitoring the state of the Nodes and taking necessary actions to keep the application running.

node-controller

Replication Controller

  • It is responsible for monitoring the status of replicasets and ensuring that the desired number of pods are available at all time within the set.

replication-controller

Other Controllers

  • There are many more such controllers available within kubernetes

other-controllers

Installing Kube-Controller-Manager

  • When you install kube-controller-manager the different controllers will get installed as well.
  • Download the kube-controller-manager binary from the kubernetes release page. For example: You can download kube-controller-manager v1.13.0 here kube-controller-manager
    $ wget https://storage.googleapis.com/kubernetes-release/release/v1.13.0/bin/linux/amd64/kube-controller-manager
    
  • By default all controllers are enabled, but you can choose to enable specific one from kube-controller-manager.service
    $ cat /etc/systemd/system/kube-controller-manager.service
    
    kube-controller-manager

View kube-controller-manager - kubeadm

  • kubeadm deploys the kube-controller-manager as a pod in kube-system namespace
    $ kubectl get pods -n kube-system
    
    kube-controller-manager0

View kube-controller-manager options - kubeadm

  • You can see the options within the pod located at /etc/kubernetes/manifests/kube-controller-manager.yaml
    $ cat /etc/kubernetes/manifests/kube-controller-manager.yaml
    
    kube-controller-manager1

View kube-controller-manager options - Manual

  • In a non-kubeadm setup, you can inspect the options by viewing the kube-controller-manager.service

    $ cat /etc/systemd/system/kube-controller-manager.service
    

    kube-controller-manager2

  • You can also see the running process and affective options by listing the process on master node and searching for kube-controller-manager.

    $ ps -aux |grep kube-controller-manager
    

    kube-controller-manager3

K8s Referenece Docs: