Did you also set https://godoc.org/google.golang.org/grpc/keepalive#EnforcementPolicy on the server? The default permitted value for time between client pings is 5 minutes ... if you set your client to ping every 30 seconds you'll need to set a matching policy on the gRPC server as well.
We've been using the gRPC keepalives on both the client and server in production for quite some time now. The main thing is making sure you get the settings correct on both sides.

Thanks for reminding, but my grpc server is based on c++. Is there any counterpart of EnforcementPolicy in grpc c++?

I believe the C++ server still wraps gRPC core. You can find the settings here:
https://github.com/grpc/grpc/blob/master/doc/keepalive.md

Make sure to pay attention to the GRPC_ARG_HTTP2_MIN_RECV_PING_INTERVAL_WITHOUT_DATA_MS,GRPC_ARG_HTTP2_MAX_PINGS_WITHOUT_DATA, GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS settings.

I tried the following configurations on c++ server and golang client to make sure that the permitted ping interval of c++(5 minutes by default) is smaller than the golang client, but it still doesn't work.

grpc::ServerBuilder builder;
// Listen on the given address without any authentication mechanism.
builder.AddListeningPort(FLAGS_address, grpc::InsecureServerCredentials());
// Enable to send HTTP2 keepalive pings over the transport.
builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS, 1);
builder.AddChannelArgument(GRPC_ARG_HTTP2_MAX_PINGS_WITHOUT_DATA, 0);

ctx := context.Background()
        ctx, cancel := context.WithCancel(ctx)
        defer cancel()

        mux := runtime.NewServeMux()
        opts := []grpc.DialOption{
                grpc.WithInsecure(),
                grpc.WithKeepaliveParams(keepalive.ClientParameters{
                        Time:                10 * time.Minute,
                        Timeout:             20 * time.Second,
                        PermitWithoutStream: true,
                }),
        }
        err := gw.RegisterMyHandlerFromEndpoint(ctx, mux, *echoEndpoint, opts)

You definitely need to ping more often than every 10 min when using Docker / Docker Swarm. The Docker proxies timeout after 10 minutes ... we use 5 * time.Minute for the client keepalive time ... you can also try 6 as well ... anything less than 10 should keep idle connections open with Docker Swarm (or just Docker in general)

@npuichigo - hopefully you were able to resolve this?

@mastersingh24 - Yes, the problem has been solved. Thank you for your concern.