How do you build a production-ready gRPC client in Go with connection reuse and resilience?

A gRPC client wraps a ClientConn which manages a pool of HTTP/2 connections. Unlike HTTP/1.1, a single gRPC connection multiplexes many concurrent RPCs — connection reuse is critical.

// Production gRPC client setup
func newUserClient(addr string) (pb.UserServiceClient, func(), error) {
    conn, err := grpc.NewClient(addr,
        // TLS in production
        grpc.WithTransportCredentials(credentials.NewTLS(&tls.Config{})),

        // Keep-alive: detect dead connections
        grpc.WithKeepaliveParams(keepalive.ClientParameters{
            Time:                10 * time.Second,
            Timeout:             5 * time.Second,
            PermitWithoutStream: true,
        }),

        // Retry policy (built-in retry)
        grpc.WithDefaultServiceConfig(`{
            "methodConfig": [{
                "name": [{"service": "user.UserService"}],
                "retryPolicy": {
                    "maxAttempts": 3,
                    "initialBackoff": "0.1s",
                    "maxBackoff": "1s",
                    "backoffMultiplier": 2,
                    "retryableStatusCodes": ["UNAVAILABLE"]
                }
            }]
        }`),
    )
    if err != nil { return nil, nil, err }

    cleanup := func() { conn.Close() }
    return pb.NewUserServiceClient(conn), cleanup, nil
}

// Using the client — always pass context
func fetchUser(ctx context.Context, client pb.UserServiceClient, id int64) (*pb.User, error) {
    ctx, cancel := context.WithTimeout(ctx, 2*time.Second)
    defer cancel()

    return client.GetUser(ctx, &pb.GetUserRequest{Id: id})
}

// Client interceptors (middleware for outgoing calls)
conn, _ := grpc.NewClient(addr,
    grpc.WithTransportCredentials(insecure.NewCredentials()),
    grpc.WithChainUnaryInterceptor(
        metadataInterceptor, // attach trace ID to outgoing metadata
        retryInterceptor,
    ),
)

Connection sharing: share one ClientConn per target service across the entire application. HTTP/2 multiplexing means thousands of concurrent RPCs share a single TCP connection — creating a new conn per RPC defeats the purpose and wastes resources.

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