HTTP/3 overview
Warning
While HTTP/3 downstream support is deemed ready for production use, improvements are ongoing, tracked in the area-quic tag.
HTTP/3 upstream support is fine for locally controlled networks, but is not ready for general internet use, and is missing some key latency features. See details below.
HTTP/3 downstream
Downstream Envoy HTTP/3 support can be turned up via adding quic_options, ensuring the downstream transport socket is a QuicDownstreamTransport, and setting the codec to HTTP/3.
Note
Hot restart is not gracefully handled for HTTP/3 yet.
Tip
See downstream HTTP/3 configuration for example configuration.
This example configuration includes both a TCP and a UDP listener, and the TCP
listener is advertising HTTP/3 support via an alt-svc header.
By default the example configuration uses kernel UDP support, but for production performance use of BPF is strongly advised if Envoy is running with multiple worker threads.
HTTP/3 advertisement
Advertising HTTP/3 is not necessary for in-house deployments where HTTP/3 is explicitly configured, but is needed for internet facing deployments where TCP is the default, and clients such as Chrome will only attempt HTTP/3 if it is explicitly advertised.
BPF usage
Envoy will attempt to use BPF on Linux by default if multiple worker threads are configured,
but may require root, or at least sudo-with-permissions (e.g. sudo setcap cap_bpf+ep).
If multiple worker threads are configured and BPF is unsupported on the platform, or is attempted and fails, Envoy will log a warning on start-up.
Downstream stats
It is recommanded to monitor some UDP listener and QUIC connection stats:
- UDP listener downstream_rx_datagram_dropped
Non-zero means kernel’s UDP listen socket’s receive buffer isn’t large enough. In Linux, it can be configured via listener socket_options by setting prebinding socket option
SO_RCVBUFatSOL_SOCKETlevel.- QUIC connection error codes and stream reset error codes
Refer to quic_error_codes.h for the meaning of each error code.
HTTP/3 upstream
HTTP/3 upstream support is implemented, with support both for explicit HTTP/3 (for data center use) and automatic HTTP/3 (for internet use).
If you are in a controlled environment where UDP is unlikely to be blocked, you can configure it as the explicit protocol in http_protocol_options.
For internet use, configuring auto_config
with http3_protocol_options
will result in Envoy attempting to use HTTP/3 for endpoints which have explicitly advertised HTTP/3 support
via an alt-svc header.
When using auto_config with http3_protocol_options, Envoy will attempt to create a QUIC connection, then if the QUIC handshake is not complete after a short delay, will kick off a TCP connection, and will use whichever is established first.