Fixes a bug whereby servers present in multiple network areas would be
properly segmented in the Router, but not in the gRPC mirror. This would
lead servers in the current datacenter leaving from a network area
(possibly during the network area's removal) from deleting their own
records that still exist in the standard WAN area.
The gRPC client stack uses the gRPC server tracker to execute all RPCs,
even those targeting members of the current datacenter (which is unlike
the net/rpc stack which has a bypass mechanism).
This would manifest as a gRPC method call never opening a socket because
it would block forever waiting for the current datacenter's pool of
servers to be non-empty.
We have seen test flakes caused by 'concurrent map read and map write', and the race detector
reports the problem as well (prevent us from running some tests with -race).
The root of the problem is the grpc expects resolvers to be registered at init time
before any requests are made, but we were using a separate resolver for each test.
This commit introduces a resolver registry. The registry is registered as the single
resolver for the consul scheme. Each test uses the Authority section of the target
(instead of the scheme) to identify the resolver that should be used for the test.
The scheme is used for lookup, which is why it can no longer be used as the unique
key.
This allows us to use a lock around the map of resolvers, preventing the data race.
The router.Manager is already rebalancing servers for other connection pools, so it can call into our resolver to do the same.
This change allows us to remove the serf dependency from resolverBuilder, and remove Datacenter from the config.
Also revert the change to refreshServerRebalanceTimer
Rename GRPCClient to ClientConnPool. This type appears to be more of a
conn pool than a client. The clients receive the connections from this
pool.
Reduce some dependencies by adjusting the interface baoundaries.
Remove the need to create a second slice of Servers, just to pick one and throw the rest away.
Unexport serverResolver, it is not used outside the package.
Use a RWMutex for ServerResolverBuilder, some locking is read-only.
Add more godoc.
R.B. Boyer