Increase Existing Kubernetes Cluster Node Count for Flannel CNI

Problem

During cluster creation, the container CIDR value for a cluster having Flannel CNI was set to 10.20.0.0/16. This will allow for a maximum of 256 nodes considering the CNI interfaces have a /24 CIDR.

Can the Container CIDR be modified for an existing cluster to say, for example /14 to allow the addition of worker nodes beyond the current limit?

Environment

• Platform9 Managed Kubernetes - All Versions
• Flannel

Procedure

1. Contact Platform9 Support so that they make the changes in the Backend Qbert DB to update the containerCIDR to a new subnet for the cluster.
2. Once the change is done, delete cni0 and flannel0 interfaces on all the nodes part of the cluster.

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~$ sudo ip link del cni0

~$ sudo ip link del flannel0

2. Restart the PMK stack in a rolling fashion on the Master Nodes which will tear down everything including any running pods and starts over again.

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~$ systemctl stop pf9-hostagent pf9-nodeletd

~$ /opt/pf9/nodelet/nodeletd phases stop

~$ systemctl start pf9-hostagent

4. Perform the same PMK Stack restart operation in batches or all together for the Worker nodes.
5. Post that, ensure that the cni0 and flannel0 interfaces comes up with the changed CIDR values.
6. Test the pod deployment and the Pod to Pod connectivity amongst the master and worker nodes.