There are other additional settings in CentOS to make Kubernetes behave correctly. Be aware that, even if we are not using kubeadm to manage the Kubernetes cluster, the following setup should be considered while running kubelet:

1. Disable SELinux, since kubelet does not support SELinux completely:

// check the state of SELinux, if it has already been disabled, bypass below commands
$ sestatus

We can disable SELinux through the following command, or by modifying the configuration file:

// disable SELinux through command
$  sudo setenforce 0
// or modify the configuration file
$ sudo sed –I 's/ SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux

Then we'll need to reboot the machine:

// reboot is required
$ sudo reboot

2. Enable the usage of iptables. To prevent some routing errors happening, add runtime parameters:

// enable the parameters by setting them to 1
$ sudo bash -c 'echo "net.bridge.bridge-nf-call-ip6tables = 1" > /etc/sysctl.d/k8s.conf'
$ sudo bash -c 'echo "net.bridge.bridge-nf-call-iptables = 1" >> /etc/sysctl.d/k8s.conf'
// reload the configuration
$ sudo sysctl --system