Even if default HTTP2 protocol options are desired, this field must be set so that Envoy will assume that the upstream supports HTTP/2 when making new HTTP connection pool connections. Currently, Envoy only supports prior knowledge for upstream connections. Even if TLS is used with ALPN, http2_protocol_options must be specified. As an aside this allows HTTP/2 connections to happen over plain text. This has been deprecated in favor of http2_protocol_options fields in the http_protocol_options message. http2_protocol_options can be set via the cluster’s extension_protocol_options. See upstream_http_protocol_options for example usage.
global rate limitでhttp2_protocol_optionsはなぜか求められている
