yarp-cni - Yet Another Random Plugin (Kubernetes CNI Edition)

A random, simplied, and most likely kinda broken CNI implementation I started as a review work for CKA exam. TLDR: It works, its just not finished.

Components

The same binary serves 2 main functions via the PLUGIN_MODE environment variable.

PLUGIN_MODE == ROUTER (WIP)

This mode is intended to run as daemon-set. In this mode, each pod (on each Node) will do the following actions:

• On startup, it checks the ConfigMap yarp-routing-table and allocates a subnet for the node it lives on (for example a /24) and registers it back on the ConfigMap. The structure should be something like this:

apiVersion: v1
kind: ConfigMap
metadata:
  name: yarp-routing-table
  namespace: kube-system
data:
  master1: 10.244.0.0/24
  node1: 10.244.1.0/24
  node2: 10.244.2.0/24

• On startup, it writes an IPAM db file locally to the node with metadata information to be leverage by the CNI mode. The DB structure is:

{
  "CIDR": "10.244.1.0/24",
  "AllocatedIps": []
}

• A long-living process that monitors for changes in the yarp-routing-table ConfigMap and watches for changes in Nodes. On changes, it will ensure that the local ip-routes are up-to-date to ensure all pods can reach each other over the network. It essentially implements a Router/RoutingTable.

PLUGIN_MODE == CNI

This mode is invoked by Kubelet during Pod setup. This project currently implements spec 0.3.1. For more information check https://github.com/containernetworking/cni/blob/master/SPEC.md

IPAM is managed via the ipam.db file. Its similar to the host-local.