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examples: create an example for enabling and configuring retry (#3028)
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# Retry | ||
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This example shows how to enable and configure retry on gRPC clients. | ||
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## Documentation | ||
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[gRFC for client-side retry support](https://github.com/grpc/proposal/blob/master/A6-client-retries.md) | ||
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## Try it | ||
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This example includes a service implementation that fails requests three times with status | ||
code `Unavailable`, then passes the fourth. The client is configured to make four retry attempts | ||
when receiving an `Unavailable` status code. | ||
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First start the server: | ||
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```bash | ||
go run server/main.go | ||
``` | ||
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Then run the client. Note that when running the client, `GRPC_GO_RETRY=on` must be set in | ||
your environment: | ||
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```bash | ||
GRPC_GO_RETRY=on go run client/main.go | ||
``` | ||
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## Usage | ||
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### Define your retry policy | ||
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Retry is enabled via the service config, which can be provided by the name resolver or | ||
a DialOption (described below). In the below config, we set retry policy for the | ||
"grpc.example.echo.Echo" method. | ||
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MaxAttempts: how many times to attempt the RPC before failing. | ||
InitialBackoff, MaxBackoff, BackoffMultiplier: configures delay between attempts. | ||
RetryableStatusCodes: Retry only when receiving these status codes. | ||
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```go | ||
var retryPolicy = `{ | ||
"methodConfig": [{ | ||
// config per method or all methods under service | ||
"name": [{"service": "grpc.examples.echo.Echo"}], | ||
"waitForReady": true, | ||
"retryPolicy": { | ||
"MaxAttempts": 4, | ||
"InitialBackoff": ".01s", | ||
"MaxBackoff": ".01s", | ||
"BackoffMultiplier": 1.0, | ||
// this value is grpc code | ||
"RetryableStatusCodes": [ "UNAVAILABLE" ] | ||
} | ||
}] | ||
}` | ||
``` | ||
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### Providing the retry policy as a DialOption | ||
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To use the above service config, pass it with `grpc.WithDefaultServiceConfig` to | ||
`grpc.Dial`. | ||
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```go | ||
conn, err := grpc.Dial(ctx,grpc.WithInsecure(), grpc.WithDefaultServiceConfig(retryPolicy)) | ||
``` |
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/* | ||
* | ||
* Copyright 2019 gRPC authors. | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* http://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
* | ||
*/ | ||
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// Binary client is an example client. | ||
package main | ||
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import ( | ||
"context" | ||
"flag" | ||
"log" | ||
"time" | ||
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"google.golang.org/grpc" | ||
pb "google.golang.org/grpc/examples/features/proto/echo" | ||
) | ||
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var ( | ||
addr = flag.String("addr", "localhost:50052", "the address to connect to") | ||
// see https://github.com/grpc/grpc/blob/master/doc/service_config.md to know more about service config | ||
retryPolicy = `{ | ||
"methodConfig": [{ | ||
"name": [{"service": "grpc.examples.echo.Echo"}], | ||
"waitForReady": true, | ||
"retryPolicy": { | ||
"MaxAttempts": 4, | ||
"InitialBackoff": ".01s", | ||
"MaxBackoff": ".01s", | ||
"BackoffMultiplier": 1.0, | ||
"RetryableStatusCodes": [ "UNAVAILABLE" ] | ||
} | ||
}]}` | ||
) | ||
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// use grpc.WithDefaultServiceConfig() to set service config | ||
func retryDial() (*grpc.ClientConn, error) { | ||
return grpc.Dial(*addr, grpc.WithInsecure(), grpc.WithDefaultServiceConfig(retryPolicy)) | ||
} | ||
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func main() { | ||
flag.Parse() | ||
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// Set up a connection to the server. | ||
conn, err := retryDial() | ||
if err != nil { | ||
log.Fatalf("did not connect: %v", err) | ||
} | ||
defer func() { | ||
if e := conn.Close(); e != nil { | ||
log.Printf("failed to close connection: %s", e) | ||
} | ||
}() | ||
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c := pb.NewEchoClient(conn) | ||
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ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second) | ||
defer cancel() | ||
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reply, err := c.UnaryEcho(ctx, &pb.EchoRequest{Message: "Try and Success"}) | ||
if err != nil { | ||
log.Fatalf("UnaryEcho error: %v", err) | ||
} | ||
log.Printf("UnaryEcho reply: %v", reply) | ||
} |
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/* | ||
* | ||
* Copyright 2019 gRPC authors. | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* http://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
* | ||
*/ | ||
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// Binary server is an example server. | ||
package main | ||
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import ( | ||
"context" | ||
"flag" | ||
"fmt" | ||
"log" | ||
"net" | ||
"sync" | ||
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"google.golang.org/grpc" | ||
"google.golang.org/grpc/codes" | ||
pb "google.golang.org/grpc/examples/features/proto/echo" | ||
"google.golang.org/grpc/status" | ||
) | ||
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var port = flag.Int("port", 50052, "port number") | ||
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type failingServer struct { | ||
mu sync.Mutex | ||
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reqCounter uint | ||
reqModulo uint | ||
} | ||
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// this method will fail reqModulo - 1 times RPCs and return status code Unavailable, | ||
// and succeeded RPC on reqModulo times. | ||
func (s *failingServer) maybeFailRequest() error { | ||
s.mu.Lock() | ||
defer s.mu.Unlock() | ||
s.reqCounter++ | ||
if (s.reqModulo > 0) && (s.reqCounter%s.reqModulo == 0) { | ||
return nil | ||
} | ||
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return status.Errorf(codes.Unavailable, "maybeFailRequest: failing it") | ||
} | ||
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func (s *failingServer) UnaryEcho(ctx context.Context, req *pb.EchoRequest) (*pb.EchoResponse, error) { | ||
if err := s.maybeFailRequest(); err != nil { | ||
log.Println("request failed count:", s.reqCounter) | ||
return nil, err | ||
} | ||
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log.Println("request succeeded count:", s.reqCounter) | ||
return &pb.EchoResponse{Message: req.Message}, nil | ||
} | ||
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func (s *failingServer) ServerStreamingEcho(req *pb.EchoRequest, stream pb.Echo_ServerStreamingEchoServer) error { | ||
return status.Error(codes.Unimplemented, "RPC unimplemented") | ||
} | ||
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func (s *failingServer) ClientStreamingEcho(stream pb.Echo_ClientStreamingEchoServer) error { | ||
return status.Error(codes.Unimplemented, "RPC unimplemented") | ||
} | ||
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func (s *failingServer) BidirectionalStreamingEcho(stream pb.Echo_BidirectionalStreamingEchoServer) error { | ||
return status.Error(codes.Unimplemented, "RPC unimplemented") | ||
} | ||
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func main() { | ||
flag.Parse() | ||
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address := fmt.Sprintf(":%v", *port) | ||
lis, err := net.Listen("tcp", address) | ||
if err != nil { | ||
log.Fatalf("failed to listen: %v", err) | ||
} | ||
fmt.Println("listen on address", address) | ||
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s := grpc.NewServer() | ||
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// Configure server to pass every fourth RPC; | ||
// client is configured to make four attempts. | ||
failingservice := &failingServer{ | ||
reqCounter: 0, | ||
reqModulo: 4, | ||
} | ||
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pb.RegisterEchoServer(s, failingservice) | ||
if err := s.Serve(lis); err != nil { | ||
log.Fatalf("failed to serve: %v", err) | ||
} | ||
} |