How to Implement Robust gRPC Stream Reconnection?

Best Practice for Reconnecting a gRPC Client

Maintaining resilience in your gRPC client-server communication is crucial, especially when pod recycling can occur. This guide provides a comprehensive solution to handle automatic reconnection and establish new streams seamlessly.

Automatic RPC Connection Management

gRPC's clientconn.go seamlessly handles RPC connections, ensuring automatic re-establishment when necessary. However, it's important to note that this mechanism extends solely to RPC connections, not the underlying stream.

Stream Reconnection

When a stream breaks, whether due to RPC connection failure or other factors, automatic reconnection is not supported. To address this, the client must obtain a new stream after the RPC connection has been re-established.

Reconnection Logic

Here's a revised solution that incorporates the correct implementation for waiting until the connection is ready and establishing a new stream:

func (grpcclient *gRPCClient) ProcessRequests() error {
    defer grpcclient.Close()

    go grpcclient.process()
    for {
        select {
        case <-grpcclient.reconnect:
            if !grpcclient.waitUntilReady(60 * time.Second) {
                return errors.New("failed to establish a connection within the defined timeout")
            }
            go grpcclient.process()
        case <-grpcclient.done:
            return nil
        }
    }
}

func (grpcclient *gRPCClient) process() {
    reqclient := GetStream() // Always get a new stream
    for {
        request, err := reqclient.stream.Recv()
        log.Info("Request received")
        if err == io.EOF {
            grpcclient.done <- true
            return
        }
        if err != nil {
            grpcclient.reconnect <- true
            return
        } else {
            // Process request
        }
    }
}

func (grpcclient *gRPCClient) waitUntilReady(timeout time.Duration) bool {
    ctx, cancel := context.WithTimeout(context.Background(), timeout)
    defer cancel()
    return grpcclient.conn.WaitForStateChange(ctx, connectivity.Ready)
}

This updated code addresses the previous mistakes by using the correct WaitForStateChange() function and tracking the current connection state. It also employs a Connect() function to connect the channel if it's idle.

In summary, while gRPC's RPC connection management is automated, stream reconnection requires explicit handling. By implementing the provided logic, you can achieve resilient gRPC client behavior, ensuring smooth communication even in the face of pod recycling.

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