#Kubernetes Cluster Initialization iptables error #K8s

 

The primary step to configure container runtimes is setting up system prerequisites.

For this, it usually needs loading of overlay and br_netfilter modules and then modifying kernel settings with below.

# Setup required sysctl params, these persist across reboots.
cat <<EOF | sudo tee /etc/sysctl.d/99-kubernetes-cri.conf
net.bridge.bridge-nf-call-iptables  = 1
net.ipv4.ip_forward                 = 1
net.bridge.bridge-nf-call-ip6tables = 1
EOF

# Apply sysctl params without reboot
sudo sysctl --system

Still, there may be an error as shown below appear in the time of cluster initialisztion using kubeadm init

[init] Using Kubernetes version: v1.22.0
[preflight] Running pre-flight checks
error execution phase preflight: [preflight] Some fatal errors occurred:
[ERROR FileContent--proc-sys-net-ipv4-ip_forward]: /proc/sys/net/ipv4/ip_forward contents are not set to 1
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`
To see the stack trace of this error execute with --v=5 or higher

This causes when be_netfilter module not detected and if some necessary network configurations are missing. This can be fixed.

Solution : 

•   Load the br_netfilter module again, use sudo if non-root user

modprobe br_netfilter

• set bridge iptables rules and ip_forward rule to 1. This is default setting on new linux kernels but CentOs and RHEL doesnt have this setting by default.

echo 1 > /proc/sys/net/bridge/bridge-nf-call-iptables

echo 1 > /proc/sys/net/ipv4/ip_forward

• Apply the settings using sysctl -p
• Now Run kubeadm reset before init, this will not clean CNI configuration, IPtables/IPVS tables or kubeconfig files

After this control-plane (or) master node can initialize the cluster and join worker nodes to cluster. Repeat the steps in worker nodes if the error appears while joining i.e., kubeadm join