The grpc resolver implementation is fed from changes to the
router.Router. Within the router there is a map of various areas storing
the addressing information for servers in those areas. All map entries
are of the WAN variety except a single special entry for the LAN.
Addressing information in the LAN "area" are local addresses intended
for use when making a client-to-server or server-to-server request.
The client agent correctly updates this LAN area when receiving lan serf
events, so by extension the grpc resolver works fine in that scenario.
The server agent only initially populates a single entry in the LAN area
(for itself) on startup, and then never mutates that area map again.
For normal RPCs a different structure is used for LAN routing.
Additionally when selecting a server to contact in the local datacenter
it will randomly select addresses from either the LAN or WAN addressed
entries in the map.
Unfortunately this means that the grpc resolver stack as it exists on
server agents is either broken or only accidentally functions by having
servers dial each other over the WAN-accessible address. If the operator
disables the serf wan port completely likely this incidental functioning
would break.
This PR enforces that local requests for servers (both for stale reads
or leader forwarded requests) exclusively use the LAN "area" information
and also fixes it so that servers keep that area up to date in the
router.
A test for the grpc resolver logic was added, as well as a higher level
full-stack test to ensure the externally perceived bug does not return.
Registering gRPC balancers is thread-unsafe because they are stored in a
global map variable that is accessed without holding a lock. Therefore,
it's expected that balancers are registered _once_ at the beginning of
your program (e.g. in a package `init` function) and certainly not after
you've started dialing connections, etc.
> NOTE: this function must only be called during initialization time
> (i.e. in an init() function), and is not thread-safe.
While this is fine for us in production, it's challenging for tests that
spin up multiple agents in-memory. We currently register a balancer per-
agent which holds agent-specific state that cannot safely be shared.
This commit introduces our own registry that _is_ thread-safe, and
implements the Builder interface such that we can call gRPC's `Register`
method once, on start-up. It uses the same pattern as our resolver
registry where we use the dial target's host (aka "authority"), which is
unique per-agent, to determine which builder to use.
This is the OSS portion of enterprise PR 3822.
Adds a custom gRPC balancer that replicates the router's server cycling
behavior. Also enables automatic retries for RESOURCE_EXHAUSTED errors,
which we now get for free.
* Move stats.go from grpc-internal to grpc-middleware
* Update grpc server metrics with server type label
* Add stats test to grpc-external
* Remove global metrics instance from grpc server tests
Previously, public referred to gRPC services that are both exposed on
the dedicated gRPC port and have their definitions in the proto-public
directory (so were considered usable by 3rd parties). Whereas private
referred to services on the multiplexed server port that are only usable
by agents and other servers.
Now, we're splitting these definitions, such that external/internal
refers to the port and public/private refers to whether they can be used
by 3rd parties.
This is necessary because the peering replication API needs to be
exposed on the dedicated port, but is not (yet) suitable for use by 3rd
parties.
R.B. Boyer