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    podCIDR error when creating Flannel network

    Posts: 33
    edited November 2022 in LFS258 Class Forum

    Hi,

    I'm creating a cluster using Kelsey Hightowers "Kubernetes the hard way", with some customization. I'm doing it locally using KVM, for instance. Also not HA. I intend it to be 1 cp master and 2 worker nodes.

    I'm using this manifest for Flannel:
    https://raw.githubusercontent.com/flannel-io/flannel/master/Documentation/kube-flannel.yml

    I've provisioned a CP master and a worker node. When I create the Flannel overlay network I get an error about podCIDR and the flannel ds does not come up.

    Running: kubectl -n kube-flannel logs kube-flannel-ds-ws8lj
    I get:

    1. Error registering network: failed to acquire lease: node "c2-worker1" pod cidr not assigned

    Because it's a cluster, I'm not configuring podCIDR in kubelet on the worker node:

    1. --pod-cidr string
    2. The CIDR to use for pod IP addresses, only used in standalone mode. In cluster mode, this is obtained from the master.

    https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet/

    I can manually add podCIDR to the node applying a patch:
    kubectl patch nodes c2-worker1 --patch '{"spec": {"podCIDR":"10.244.0.0/16"}}'
    Then, Flannel overlay network comes up as expected.

    What's happening here?

    Best Answer

    • Posts: 33
      Answer ✓

      I solved it.

      I needed to pass --allocate-node-cidrs=true to the kube-controller-manager.

      I'm running it as a systemd service. The start of the unit file looks like this:

      1. [Service]
      2. ExecStart=/usr/bin/kube-controller-manager \
      3.   --cluster-cidr=10.244.0.0/16 \
      4.   --allocate-node-cidrs=true \

      Now each node is assigned a /24 each and it works as expected without a manual patch.

      kubectl describe nodes | grep -i cidr

      1. PodCIDR:                      10.244.0.0/24
      2. PodCIDRs:                     10.244.0.0/24
      3. PodCIDR:                      10.244.1.0/24
      4. PodCIDRs:                     10.244.1.0/24

    Answers

    • Posts: 1

      can you please mention file name to edit

    • Posts: 33
      edited March 2023

      @nuthan That would be the systemd service file for kube-controller-manager.
      It should be somewhere under /etc/systemd/system/

      Note that kube-controller-manager would be run as a pod if you created your cluster with kubeadm.

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