Calico Node Controller for Kubernetes

NOTE: A productized version of this functionality now exists here: https://github.com/projectcalico/kube-controllers/tree/master/pkg/controllers/node

This is a prototype, WIP node controller for Kubernetes. I'm not currently intending to continue development / maintenance much further, but it might be a useful starting point for someone.

It watches Kubernetes nodes and ensures that the Calico etcd datastore remains in-sync.

Namely:

• It creates / updates any Calico Node resources when the Kubernetes representation changes.
• It deletes and Calico Node resources which do not match a Kubernetes Node.

This is useful when, for example, running a cluster in an AWS autoscaling group where nodes are commonly created / deleted, and prevents stale data from lingering in etcd.

TODOs:

• Limit to Kubernetes Nodes (currently this won't work on a mixed cluster).
• Handle disconnect / reconnect to etcd.
• Periodically populate cache to check for and overwrite modifications to Calico resources.
• Tests, tests, tests