8e0f00a3a6
At present, the relay's event-loop simply drops a UDP packet in case the socket is not ready for writing. This is terrible for throughput because it means the encapsulated packet within the WG payload needs to be retransmitted by the source after a timeout. To avoid this, we instead buffer the packet and suspend the event loop until it has been correctly flushed out. This may still cause packet loss because the receive buffer may overflow in the meantime. However, there is nothing we can do about that because UDP itself doesn't have any backpressure. The relay listens on many sockets at once via a separate worker thread and an `mio` event-loop. In addition to the current subscription to readable event, we now also subscribe to writable events. At the very top of the relay's event-loop, we insert a `flush` function that ensures all buffered packets have been written out and - in case writing a packet fails - suspends the event-loop with a waker. If we receive a new event for write-readiness, we wake the waker which will trigger a new call to `Eventloop::poll` where we again try to flush the pending packet. We don't bother with tracking exactly, which socket sent the write-readiness and which socket we have still pending packets in. Instead, we suspend the entire event-loop until all pending packets have been flushed. Resolves: #7519.
relay
This crate houses a minimalistic STUN & TURN server.
Features
We aim to support the following feature set:
- STUN binding requests
- TURN allocate requests
- TURN refresh requests
- TURN channel bind requests
- TURN channel data requests
Relaying of data through other means such as DATA frames is not supported.
Building
You can build the relay using: cargo build --release --bin firezone-relay
You should then find a binary in target/release/firezone-relay.
Running
The Firezone Relay supports Linux only. To run the Relay binary on your Linux host:
- Generate a new Relay token from the "Relays" section of the admin portal and save it in your secrets manager.
- Ensure the
FIREZONE_TOKEN=<relay_token>environment variable is set securely in your Relay's shell environment. The Relay expects this variable at startup. - Now, you can start the Firezone Relay with:
firezone-relay
To view more advanced configuration options pass the --help flag:
firezone-relay --help
Ports
By default, the relay listens on port udp/3478. This is the standard port for
STUN/TURN. Additionally, the relay needs to have access to the port range
49152 - 65535 for the allocations.
Portal Connection
When given a token, the relay will connect to the Firezone portal and wait for
an init message before commencing relay operations.
Metrics
The relay parses the OTLP_GRPC_ENDPOINT env variable.
Traces and metrics will be sent to an OTLP collector listening on that endpoint.
It is recommended to set additional environment variables to scope your metrics:
OTEL_SERVICE_NAME: Translates to theservice.name.OTEL_RESOURCE_ATTRIBUTES: Additional, comma-separated key=value attributes.
By default, we set the following OTEL attributes:
service.name=relayservice.namespace=firezone
The docker-init-relay.sh script integrates with GCE.
When OTEL_METADATA_DISCOVERY_METHOD=gce_metadata, the service.instance.id
variables is set to the instance ID of the VM.
Design
The relay is designed in a sans-IO fashion, meaning the core components do not cause side effects but operate as pure, synchronous state machines. They take in data and emit commands: wake me at this point in time, send these bytes to this peer, etc.
This allows us to very easily unit-test all kinds of scenarios because all inputs are simple values.
The main server runs in a single task and spawns one additional task for each allocation. Incoming data that needs to be relayed is forwarded to the main task where it gets authenticated and relayed on success.