control-plane: make use of k8s plugins

[yskopets]

Changes:

• replace former initialization logic with bootstrap process
• start using k8s plugins
• start using DiscoverySource API

[jakubdyszkiewicz]

Can you remind, why do we need a version here?
thanks

[yskopets]

Every resource in Envoy Delta xDS API has its own version (see https://github.com/envoyproxy/data-plane-api/blob/master/envoy/api/v2/discovery.proto#L226).

This version field is an attempt to associate that value with one that already exists in k8s/Consul.

[jakubdyszkiewicz]

With explicite versioning like in proxy template this works fine, but when you eventually want to send a list of clusters/endpoints from the generated from rules you define. Then you have to combine versions from multiple resources.
The most intuitive way is to compute hash from resources, but you can get into hash collisions, so we end up having hashmap with UUIDs for given resources group. This does not have to be shared between control plane instances because when node connects to an control plane instance, it starts with empty version.

Btw. there is no such thing as version in Consul, nor probably in any discovery system. You've got an ID of instance, but the instance data can change.

I know this is not a problem for now, but just letting you know upfront how we solved it :)

Also, I don't think that Delta xDS is fully available in Envoy right now
envoyproxy/envoy#4991
nor in go-control-plane https://github.com/envoyproxy/go-control-plane/search?q=DeltaDiscoveryRequest&unscoped_q=DeltaDiscoveryRequest

[yskopets]

In Consul it's called ModifyIndex (https://www.consul.io/api/catalog.html#modifyindex)

Delta xDS API is defined in Golang code, although without implementation for now (https://github.com/envoyproxy/go-control-plane/blob/master/pkg/server/server.go#L413-L435).

[jakubdyszkiewicz]

Yeah, just like in java-control-plane, it's defined because it's in proto.
About index, you're right. Completely forgot about ModifyIndex

Just wanted to point that we have to be aware that we may not have working Incremental xDS when we will start implementing cluster/endpoints propagation.