Envoy,gRPC 和速率限制

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Envoy是专为 Cloud Native 应用设计的轻量级服务代理,也是为数不多的支持gRPC的代理之一。gRPC 是一个基于HTTP/2的高性能 RPC(远程过程调用)框架,支持多种语言。

Envoy
Envoy

在这篇文章中,我们将使用 gRPC 和Protocol Buffers构建 C++语言版本的Greeter 应用,使用Go语言构建另一个 gRPC 应用,实现 Envoy 的RateLimitService接口。最后,将 Envoy 部署为 Greeter 应用的代理,使用我们的速率限制服务实现反压机制(backpressure)。

gRPC Greeter 应用

我们首先安装gRPCProtobuf,然后构建 C++语言版本的 Greeter 应用。您还可以通过选择文档中列出的其他语言来构建此应用程序; 但是,我将在本文中使用 C++。

以下是 Greeter 应用的示意图。

Greeter
Greeter

运行 Greeter 应用时,终端中会有以下输出:

$ ./greeter_server
Server listening on 0.0.0.0:50051
$ ./greeter_client
Greeter received: Hello world

升级 gRPC Greeter 应用

现在,我们通过使用带有请求计数前缀的返回值替代静态的“Hello”前缀,来增强 Greeter 应用。只需更新greeter_server.cc文件,如下所示。

 // Logic and data behind the server's behavior.
 class GreeterServiceImpl final : public Greeter::Service {
+  int counter = 0;
   Status SayHello(ServerContext* context, const HelloRequest* request,
                   HelloReply* reply) override {
-    std::string prefix("Hello ");
+    std::string prefix(std::to_string(++counter) + " ");
     reply->set_message(prefix + request->name());
     return Status::OK;
   }

然后重新构建和运行greeter_server,通过greeter_client发送请求时你就能看到如下输出。

$ for i in {1..3}; do ./greeter_client; sleep 1; done
Greeter received: 1 world
Greeter received: 2 world
Greeter received: 3 world

简单速率限制服务

接下来,我们通过扩展 Envoy 的RateLimitService原型接口,用 Go 语言实现一个简单的速率限制服务。为此,我们创建一个名为rate-limit-service的 Go 项目,并引入 Envoy 的go-control-plane和其它相关依赖。go-control-plane项目为 Envoy 原型提供了 Go 语言绑定。为了后续实现速率限制服务,我们还需创建cmd/server/main.gocmd/client/main.go两个文件。

$ mkdir -p $GOPATH/src/github.com/venilnoronha/rate-limit-service/
$ cd $GOPATH/src/github.com/venilnoronha/rate-limit-service/
$ mkdir -p cmd/server/ && touch cmd/server/main.go
$ mkdir cmd/client/ && touch cmd/client/main.go

引入了所有依赖之后,你将获得一个如下所示的项目结构。注意我只突出列出了这个实验相关的包。

── rate-limit-service
   ├── cmd
   │   ├── client
   │   │   └── main.go
   │   └── server
   │       └── main.go
   └── vendor
       ├── github.com
       │   ├── envoyproxy
       │   │   ├── data-plane-api
       │   │   └── go-control-plane
       │   ├── gogo
       │   │   ├── googleapis
       │   │   └── protobuf
       │   └── lyft
       │       └── protoc-gen-validate
       └── google.golang.org
           ├── genproto
           └── grpc

速率限制服务端

现在,我们创建一个简单的 gRPC 速率限制服务,来限制每秒的请求数(译者注:例子实现是交替限制请求)。

package main

import (
    "log"
    "net"
    "golang.org/x/net/context"
    "google.golang.org/grpc"
    "google.golang.org/grpc/reflection"
    rls "github.com/envoyproxy/go-control-plane/envoy/service/ratelimit/v2"
)

// server is used to implement rls.RateLimitService
type server struct{
	// limit specifies if the next request is to be rate limited
	limit bool
}

func (s *server) ShouldRateLimit(ctx context.Context,
		request *rls.RateLimitRequest) (*rls.RateLimitResponse, error) {
	log.Printf("request: %v\n", request)

	// logic to rate limit every second request
	var overallCode rls.RateLimitResponse_Code
	if s.limit {
		overallCode = rls.RateLimitResponse_OVER_LIMIT
		s.limit = false
	} else {
		overallCode = rls.RateLimitResponse_OK
		s.limit = true
	}

	response := &rls.RateLimitResponse{OverallCode: overallCode}
	log.Printf("response: %v\n", response)
        return response, nil
}

func main() {
	// create a TCP listener on port 50052
        lis, err := net.Listen("tcp", ":50052")
        if err != nil {
                log.Fatalf("failed to listen: %v", err)
        }
	log.Printf("listening on %s", lis.Addr())

	// create a gRPC server and register the RateLimitService server
        s := grpc.NewServer()
	rls.RegisterRateLimitServiceServer(s, &server{limit: false})
        reflection.Register(s)
        if err := s.Serve(lis); err != nil {
                log.Fatalf("failed to serve: %v", err)
        }
}

启动RateLimitService服务之后,终端输出如下。

$ go run cmd/server/main.go
2018/10/27 00:35:28 listening on [::]:50052

速率限制客户端

我们同样创建一个RateLimitService的客户端来验证服务端的行为。

package main

import (
        "log"
	"time"
        "golang.org/x/net/context"
        "google.golang.org/grpc"
	rls "github.com/envoyproxy/go-control-plane/envoy/service/ratelimit/v2"
)

func main() {
        // Set up a connection to the server
        conn, err := grpc.Dial("localhost:50052", grpc.WithInsecure())
        if err != nil {
                log.Fatalf("could not connect: %v", err)
        }
        defer conn.Close()
        c := rls.NewRateLimitServiceClient(conn)

        // Send a request to the server
        ctx, cancel := context.WithTimeout(context.Background(), time.Second)
        defer cancel()
	r, err := c.ShouldRateLimit(ctx, &rls.RateLimitRequest{Domain: "envoy"})
        if err != nil {
                log.Fatalf("could not call service: %v", err)
        }
        log.Printf("response: %v", r)
}

现在让我们通过启动客户端来测试服务端/客户端的交互。

$ for i in {1..4}; do go run cmd/client/main.go; sleep 1; done
2018/10/27 17:32:23 response: overall_code:OK
2018/10/27 17:32:25 response: overall_code:OVER_LIMIT
2018/10/27 17:32:26 response: overall_code:OK
2018/10/27 17:32:28 response: overall_code:OVER_LIMIT

服务端的相关日志。

2018/10/27 17:32:23 request: domain:"envoy"
2018/10/27 17:32:23 response: overall_code:OK
2018/10/27 17:32:25 request: domain:"envoy"
2018/10/27 17:32:25 response: overall_code:OVER_LIMIT
2018/10/27 17:32:26 request: domain:"envoy"
2018/10/27 17:32:26 response: overall_code:OK
2018/10/27 17:32:28 request: domain:"envoy"
2018/10/27 17:32:28 response: overall_code:OVER_LIMIT

Envoy 代理

现在我们引入 Envoy 代理,它将来自 Greeter 客户端的请求路由到 Greeter 服务端,同时使用我们的速率限制服务检查速率。下图描述了我们最终的部署结构。

envoy proxy
envoy proxy

代理配置

我们使用如下 Envoy 配置来注册 Greeter 和 RateLimitService 服务并启用限速检查。注意,由于我们是将 Envoy 部署在Docker for Mac上,本地部署的服务是通过docker.for.mac.localhost地址引用的。

static_resources:
  listeners:
  - address:
      socket_address:
        address: 0.0.0.0
        port_value: 9211 # expose proxy on port 9211
    filter_chains:
    - filters:
      - name: envoy.http_connection_manager
        config:
          codec_type: auto
          stat_prefix: ingress_http
          access_log: # configure logging
            name: envoy.file_access_log
            config:
              path: /dev/stdout
          route_config:
            name: greeter_route # configure the greeter service routes
            virtual_hosts:
            - name: service
              domains:
              - "*"
              routes:
              - match:
                  prefix: "/"
                  grpc: {}
                route:
                  cluster: greeter_service
              rate_limits: # enable rate limit checks for the greeter service
                actions:
                - destination_cluster: {}
          http_filters:
          - name: envoy.rate_limit # enable the Rate Limit filter
            config:
              domain: envoy
          - name: envoy.router # enable the Router filter
            config: {}
  clusters:
  - name: greeter_service # register the Greeter server
    connect_timeout: 1s
    type: strict_dns
    lb_policy: round_robin
    http2_protocol_options: {} # enable H2 protocol
    hosts:
    - socket_address:
        address: docker.for.mac.localhost
        port_value: 50051
  - name: rate_limit_service # register the RateLimitService server
    connect_timeout: 1s
    type: strict_dns
    lb_policy: round_robin
    http2_protocol_options: {} # enable H2 protocol
    hosts:
    - socket_address:
        address: docker.for.mac.localhost
        port_value: 50052
rate_limit_service: # define the global rate limit service
  use_data_plane_proto: true
  grpc_service:
    envoy_grpc:
      cluster_name: rate_limit_service

部署 Envoy 代理

为了部署 Envoy 代理,我们将上述配置拷贝到envoy.yaml文件。然后我们使用如下的Dockerfile构建 Docker 镜像。

FROM envoyproxy/envoy:latest
COPY envoy.yaml /etc/envoy/envoy.yaml

使用如下命令构建镜像:

$ docker build -t envoy:grpc .
Sending build context to Docker daemon  74.75kB
Step 1/2 : FROM envoyproxy/envoy:latest
 ---> 51fc619e4dc5
Step 2/2 : COPY envoy.yaml /etc/envoy/envoy.yaml
 ---> c766ba3d7d09
Successfully built c766ba3d7d09
Successfully tagged envoy:grpc

然后运行代理:

$ docker run -p 9211:9211 envoy:grpc
...
[2018-10-28 02:59:20.469][000008][info][main] [source/server/server.cc:456] starting main dispatch loop
[2018-10-28 02:59:20.553][000008][info][upstream] [source/common/upstream/cluster_manager_impl.cc:135] cm init: all clusters initialized
[2018-10-28 02:59:20.554][000008][info][main] [source/server/server.cc:425] all clusters initialized. initializing init manager
[2018-10-28 02:59:20.554][000008][info][config] [source/server/listener_manager_impl.cc:908] all dependencies initialized. starting workers

更新 Greeter 客户端

由于要使用 Envoy 路由 Greeter 客户端的请求,我们将客户端代码中的服务端端口从50051改为9211,并重新 build。

   GreeterClient greeter(grpc::CreateChannel(
-      "localhost:50051", grpc::InsecureChannelCredentials()));
+      "localhost:9211", grpc::InsecureChannelCredentials()));
   std::string user("world");
   std::string reply = greeter.SayHello(user);

最终测试

此时,我们已经有了 Greeter 服务端、RateLimitService 服务和一个 Envoy 代理,是时候验证整个部署了。为此,我们使用更新后的 Greeter 客户端发送几个如下所示的请求(译者注:前面 Greeter 服务端没有停,counter 已经到了 3)。

$ for i in {1..10}; do ./greeter_client; sleep 1; done
Greeter received: 4 world
14:
Greeter received: RPC failed
Greeter received: 5 world
14:
Greeter received: RPC failed
Greeter received: 6 world
14:
Greeter received: RPC failed
Greeter received: 7 world
14:
Greeter received: RPC failed
Greeter received: 8 world
14:
Greeter received: RPC failed

如你所见,10 个请求中的 5 个是成功的,交替出现 gRPC 状态码为14RPC failed失败请求。这表明速率限制服务按照设计限制了请求,Envoy 正确地终止了之后的请求。

结论

这篇文章让你对如何使用 Envoy 作为应用代理有了一个高层次的认识,也能帮助你理解 Envoy 的限速过滤器如何跟 gRPC 协议协同工作。

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