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gRPC Web Proxy

This is a small reverse proxy that can front existing gRPC servers and expose their functionality using gRPC-Web protocol, allowing for the gRPC services to be consumed from browsers.

Features:

  • structured logging of proxied requests to stdout
  • debug HTTP endpoint (default on port 8080)
  • Prometheus monitoring of proxied requests (/metrics on debug endpoint)
  • Request (/debug/requests) and connection tracing endpoints (/debug/events)
  • TLS 1.2 serving (default on port 8443):
    • with option to enable client side certificate validation
  • both secure (plaintext) and TLS gRPC backend connectivity:
    • with customizable CA certificates for connections

The intended use is as a companion process for gRPC server containers.

Installing

Pre-built binaries

There are pre-built binaries available for Windows, Mac and Linux (ARM and x86_64): https://github.com/improbable-eng/grpc-web/releases

Building from source

To build, you need to have Go >= 1.8, and call go get with dep ensure:

GOPATH=~/go ; export GOPATH
git clone https://github.com/improbable-eng/grpc-web.git $GOPATH/src/github.com/improbable-eng/grpc-web
cd $GOPATH/src/github.com/improbable-eng/grpc-web
dep ensure # after installing dep
go install ./go/grpcwebproxy # installs into $GOPATH/bin/grpcwebproxy

Running

Here's a simple example that fronts a local, TLS gRPC server:

grpcwebproxy
    --server_tls_cert_file=../../misc/localhost.crt \
    --server_tls_key_file=../../misc/localhost.key \
    --backend_addr=localhost:9090 \
    --backend_tls_noverify

Running specific servers

By default, grpcwebproxy will run both TLS and HTTP debug servers. To disable either one, set the --run_http_server or --run_tls_server flags to false.

For example, to only run the HTTP server, run the following:

grpcwebproxy
    --backend_addr=localhost:9090 \
    --run_tls_server=false

Enabling Websocket Transport

By default, grpcwebproxy will not use websockets as a transport layer. To enable websockets, set the --use_websockets flag to true.

$GOPATH/bin/grpcwebproxy \
    --backend_addr=localhost:9090 \
    --use_websockets

Changing the Maximum Receive Message Size

By default, grpcwebproxy will limit the message size that the backend sends to the client. This is currently 4MB. To override this, set the --backend_max_call_recv_msg_size flag to an integer with the desired byte size.

For example, to increase the size to 5MB, set the value to 5242880 (5 * 1024 * 1024).

grpcwebproxy \
    --backend_max_call_recv_msg_size=5242880

Note that if you set a lower value than 4MB, the lower value will be used. Also, it is preferrable to send data in a stream than to set a very large value.

Configuring CORS for Http and WebSocket connections

By default, grpcwebproxy will reject any request originating from a client running on any domain other than that of where the server is hosted, this can be configured via one of the --allow_all_origins or --allowed_origins flags.

For example, to allow requests from any origin:

grpcwebproxy \
    --allow_all_origins

Or to only allow requests from a specific list of origins:

grpcwebproxy \
    --allowed_origins=https://example.org,https://awesome.com