This article shows you how to proxy client HTTP traffic to the back-end gRPC service via the grpc-transcode plugin in Apache .

Introduction​

Apache ​

Apache is a dynamic, real-time, high-performance API gateway that provides load balancing, dynamic upstream, canary release, service fusion, authentication, observability, and other rich traffic management features. Apache not only supports dynamic change and hot-plugging of plug-ins, but also has a rich library of plug-in resources.

gRPC​

gRPC is an open source remote procedure call system initiated by Google. The system is based on HTTP/2 protocol transport, using Protocol Buffers as the interface description language, and can be run in any environment. The gRPC service provides pluggable mode support for load balancing, link tracing, health checking, and authentication, effectively connecting multiple services between data centers.

Plugin Introduction​

In order to add support for gRPC service proxies, Apache has released grpc-transcode, a gRPC-based plugin that invokes gRPC services in a RESTful way.

The plugin supports specifying the contents of .proto files in Apache and implementing proxies for different gRPC services through user-defined gRPC services.

Integration Principle​

The user specifies the .proto content in Apache , binds the corresponding proto by the proto_id in the grpc-transcode plugin, and configures the Service and Method defined in the .proto to implement a proxy for the gRPC service.

The basic principle is as follows: the user can configure a grpc-transcode plugin in the route, and when the route matches the request, it will forward the gRPC request to the upstream service.

How to use​

Environment Preparation​

Before configuring Apache , you need to start the gRPC service.

Step 1: Configure the grpc-server-example service​

1. Clone the grpc-server-example repository.

git clone https://github.com/api7/grpc_server_example

2. Start grpc-server.

cd grpc_server_examplego run main.go

3. Verify the gRPC service, it is recommended to use grpcurl to verify the availability of the service.

grpcurl -d '{"name": "zhangsan"}' -plaintext 127.0.0.1:50051 helloworld.Greeter.SayHello

After correctly starting the gRPC service, executing the above command will output the following.

{ "message": "Hello zhangsan"}

Step 2: Configure Apache ​

1. Add proto

curl http://127.0.0.1:9080//admin/proto/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '{    "content" : "syntax = \"proto3\";    package helloworld;    service Greeter {        rpc SayHello (HelloRequest) returns (HelloReply) {}    }    message HelloRequest {        string name = 1;    }    message HelloReply {        string message = 1;    }"}'

2. In the specified Route, proxy the gRPC service interface.

curl http://127.0.0.1:9080//admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '{    "methods": ["GET"],    "uri": "/grpctest",    "plugins": {        "grpc-transcode": {         "proto_id": "1",         "service": "helloworld.Greeter",         "method": "SayHello"        }    },    "upstream": {        "scheme": "grpc",        "type": "roundrobin",        "nodes": {            "127.0.0.1:50051": 1        }    }}'

Details of the specific code interpretation and supported parameters can be found below.

Testing Requests​

Here we will use cURL for testing.

curl -i http://127.0.0.1:9080/grpctest\?name=worldHTTP/1.1 200 OKDate: Mon, 27 Dec 2021 06:24:47 GMTContent-Type: application/jsonTransfer-Encoding: chunkedConnection: keep-aliveServer: /2.11.0Trailer: grpc-statusTrailer: grpc-message{"message":"Hello world"}grpc-status: 0grpc-message:

The feedback from the code shows that the request was successfully proxied to the back-end gRPC service.

Disabling the plugin​

If you are done using the grpc-transcode plugin on the route, simply remove the plugin-related configuration from the route configuration to turn off the grpc-transcode plugin on the route.

Thanks to the Apache plugin hot-loading mode, there is no need to restart Apache to turn it on and off.

# Disable the plugincurl http://127.0.0.1:9080//admin/routes/111 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '{    "methods": ["GET"],    "uri": "/grpctest",    "plugins": {},    "upstream": {        "scheme": "grpc",        "type": "roundrobin",        "nodes": {            "127.0.0.1:50051": 1        }    }}'

Summary​

This article provides a step-by-step guide to using the grpc-transcode plugin to proxy requests to a back-end gRPC service via RESTful. By using this plugin, Apache can be configured to proxy to the gRPC service only.

For more descriptions and a complete configuration list of the grpc-transcode plugin, please refer to the official documentation.