Unpin gRPC

[yurishkuro]

For some reason #1492 pinned gRPC to a specific release, we need to unpin it. It will require resolving these issues:

Detected staticcheck failures:
cmd/agent/app/reporter/grpc/builder.go:133:36: grpc.WithBalancerName is deprecated: use WithDefaultServiceConfig and WithDisableServiceConfig instead.  Will be removed in a future 1.x release.  (SA1019)
pkg/discovery/grpcresolver/grpc_resolver_test.go:146:78: grpc.WithBalancerName is deprecated: use WithDefaultServiceConfig and WithDisableServiceConfig instead.  Will be removed in a future 1.x release.  (SA1019)
make: *** [lint-staticcheck] Error 1

[guanw]

@yurishkuro I can work on this since I introduced WithBalancerName

[guanw]

WithDefaultServiceConfig introduces a json string serviceConfig that looks like this, should we also introduce a flag for this which defaults to {"loadBalancingPolicy":"round_robin"}

[guanw]

Also when I comment out override section for google.golang.org/grpc in toml file and do dep ensure -update google.golang.org/grpc, the following error shows (incomplete log):

Looks like @objectiser introduces the revision. Any idea we are pinning jaeger-client-go to 6733ee486c780528f2c8088305e16fdb685134c7 (Can we remove this constraint first)?

[yurishkuro]

I already have a PR to remove client pin: #1780

[yurishkuro]

WithDefaultServiceConfig introduces a json string serviceConfig

I assume json is an option, not a requirement, i.e. do we still have programmatic way to configure? I prefer we fix the main issue first, not introduce new configuration options.

[guanw]

@yurishkuro See grpc/grpc-go#3003, looks like that's the only recommended way. We can put a const serviceConfig = <service config json string> for now to avoid setting flags.