• How are the virtual bridges in the nodes assigned an IP subnet?
  • How are the Pod assigned an IP?
  • Where is the information stored?
  • How are duplicate IP not assigned?
  • CNI Plugin Responsibilities:
    • Must support arguments ADD/DEL/CHECK.
    • Must support parameters container id, network ns.
    • Must manage IP Address assignment to PODs.
    • Must return results in a specific format.
  • How assign IP Address?
  • How do we not assign duplicate IPs during the ip -n <namespace> addr add and ip -n <namespace> route add commands?
    • An easy way is to store all required IPs in a file.
  • The file would look like this: 
    IP         STATUS   POD
10.244.1.2 ASSIGNED BLUE
  • The above file is placed on each host and the IPs of each pod per host are assigned appropriately.
  • In the network assignment script, you’d add ip = get_free_ip_from_file() before running the ip -n names.
  • You can outsource the above actually and use two built-in plugins with CNI –> DHCP and host-local
    • You’d call that in the network assignment script with ip = get_free_ip_from_host_local()
  • The CNI has a configuration file under /etc/cni/net.d/net-script.conf. It looks like this: ``` { “cniVersion”: “0.2.0”, “name”: “mynet”, “type”: “net-script”, “bridge”: “cni0”, “isGateway”: true, “ipMasq”: true, “ipam”: { “type”: “host-local”, “subnet”: “10.244.0.0/16”, “routes”: { { “dst”: “0.0.0.0/0” } }

} ```

  • The above ipam section is the one of interest with CNI.
    • The ipam config settings are read from the network assignment script.
  • WEAVEWORKS by default allocates the IP range of 10.32.0.0/12 for the entire network.
    • Provides an IP range of 10.32.0.1 to 10.47.255.254. 1,048,574 IPs are available.
      • This is now split between each node. Node A is assigned 10.32.0.1, Node B is assigned 10.38.0.0 and Node C is assigned 10.44.0.0. This is for the pods, not the actual node IPs themselves.

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