grpc bump: Implement master/client/v3/naming new endpointManager & resolver

[ptabor]

Naming

In order to migrate out of decommissioned in grpc-1.30 APIs of naming (and picker),
still addressing the use-cases documented in:
https://github.com/etcd-io/etcd/blob/master/Documentation/dev-guide/grpc_naming.md

We execute following plan:

1. Introduce new interfaces as defined in: Replacement API for client/v3/naming package to be compatible with new GRPC1.30+ resolver API. #12614
2. Implement them [help needed]
3. Migrate grpc proxy on the new implementation. This is hopefully ready:(ptabor@142b9a3)

Picker

Apart of dealing with clientv3/naming as documented above,
we need to migrate clientv3/balancer on a new picker.
The code from contributions like:
#12384
#12636
#12439
Might be good for this (when isolated and passing test).
Mid term I would think why/whether etcd needs own balancer and why just:
https://pkg.go.dev/google.golang.org/grpc@v1.35.0/balancer/roundrobin
on top of some 'passthrough' like https://pkg.go.dev/google.golang.org/grpc/resolver

[lemonlinger]

I'd like to claim this task. Is there a deadline for this?

[ptabor]

@lemonlinger Thank you. Many users are waiting for moving that dependency forward, so I hope to have it completed in O(2) weeks. We can decouple this into smaller pieces:

1. [Done in Implement Update method for EndpointManager #12667] Write variant of the resolver_test(

   etcd/tests/integration/clientv3/naming/resolver_test.go

   Line 56 in 50ca440

   conn, err := grpc.Dial("etc://foo", grpc.WithResolvers(etcdResolver))

   ) that uses the old API: https://etcd.io/docs/v3.3.12/dev-guide/grpc_naming/

2. [Done in Implement Update method for EndpointManager #12667] EndpointManager add/delete (

   etcd/client/v3/naming/endpoints/endpoints_impl.go

   Line 22 in 50ca440

   func (m *endpointManager) Update(ctx context.Context, updates []*UpdateWithOpts) error {

   ) implementation

3. [Done in Implement Update method for EndpointManager #12667] Write variant of the resolver_test(

   etcd/tests/integration/clientv3/naming/resolver_test.go

   Line 56 in 50ca440

   conn, err := grpc.Dial("etc://foo", grpc.WithResolvers(etcdResolver))

   ) that uses new endpointManager, but old resolver code

4. Implementation of new Endpoint Watch (& List DONE]

5. Resolver on top of Endpoint Watch

6. Final resolver_test that entirely uses new API.

I think 1&2 can be done in parallel and its better to claim smaller pieces of work.

[lemonlinger]

@peterbourgon OK

[ptabor]

3 more PRs to merge:

• clientv3: Replace balancer with upstream grpc solution #12671 (replace custom balancer with upstream grpc)
• Cleanup grpc client/v3/naming API #12675 (migrate grpcproxy and cleanup)
• Update grpc dependency to 1.32. #12709 bump to grpc-1.32

And that's a wrap.

[ptabor]

In my fork (https://github.com/ptabor/etcd/tree/20210210-grpc-bump) I have version with the PRs applies + 1 test fix + grpc-1.32 bump that passes all the tests