- Use some protobuf construction helper methods for brevity.
- Rename a local variable to avoid later shadowing.
- Rename the Nonce field to be more like xDS's naming.
- Be more explicit about which PeerID fields are empty.
If someone were to switch a peer-exported service from L4 to L7 there
would be a brief SAN validation hiccup as traffic shifted to the mesh
gateway for termination.
This PR sends the mesh gateway SpiffeID down all the time so the clients
always expect a switch.
For L4/tcp exported services the mesh gateways will not be terminating
TLS. A caller in one peer will be directly establishing TLS connections
to the ultimate exported service in the other peer.
The caller will be doing SAN validation using the replicated SpiffeID
values shipped from the exporting side. There are a class of discovery
chain edits that could be done on the exporting side that would cause
the introduction of a new SpiffeID value. In between the time of the
config entry update on the exporting side and the importing side getting
updated peer stream data requests to the exported service would fail due
to SAN validation errors.
This is unacceptable so instead prohibit the exporting peer from making
changes that would break peering in this way.
Because peerings are pairwise, between two tuples of (datacenter,
partition) having any exported reference via a discovery chain that
crosses out of the peered datacenter or partition will ultimately not be
able to work for various reasons. The biggest one is that there is no
way in the ultimate destination to configure an intention that can allow
an external SpiffeID to access a service.
This PR ensures that a user simply cannot do this, so they won't run
into weird situations like this.
Peer replication is intended to be between separate Consul installs and
effectively should be considered "external". This PR moves the peer
stream replication bidirectional RPC endpoint to the external gRPC
server and ensures that things continue to function.
