gRPC is an RPC framework from Google. It uses protocol buffers as the underlying serialization/IDL format. At the transport layer it uses HTTP/2 for request/response multiplexing. Envoy has first class support for gRPC both at the transport layer as well as at the application layer:
- gRPC makes use of HTTP/2 trailers to convey request status. Envoy is one of very few HTTP proxies that correctly supports HTTP/2 trailers and is thus one of the few proxies that can transport gRPC requests and responses.
- The gRPC runtime for some languages is relatively immature. Envoy supports a gRPC bridge filter that allows gRPC requests to be sent to Envoy over HTTP/1.1. Envoy then translates the requests to HTTP/2 for transport to the target server. The response is translated back to HTTP/1.1.
- When installed, the bridge filter gathers per RPC statistics in addition to the standard array of global HTTP statistics.
- gRPC-Web is supported by a filter that allows a gRPC-Web client to send requests to Envoy over HTTP/1.1 and get proxied to a gRPC server. It’s under active development and is expected to be the successor to the gRPC bridge filter.