How to Handle gRPC Client Reconnection in Kubernetes When Server Pods Recycle?

How to Properly Reconnect a Go gRPC Client

Introduction

Maintaining robust connections is crucial for reliable gRPC communication. This article addresses how to effectively handle client reconnections when the connected server pod is recycled in a Kubernetes cluster.

Problem

gRPC clients rely on a ClientConn to establish and manage connections. However, automatic reconnection doesn't always extend to streams once they are broken. This issue arises when a server pod is recycled, causing the stream to be lost and the connection to fail.

Solution

Option 1: Manual Stream Handling

To address the problem, you need to manually establish a new stream whenever the connection drops. The following code demonstrates how to wait for the RPC connection to be ready while creating and processing new streams:

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

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

func (grpcclient *gRPCClient) process() {
    // Create a new stream whenever the function is called
    reqclient := GetStream()
    for {
        request, err := reqclient.stream.Recv()
        if err == io.EOF {
            grpcclient.done <- true
            return
        }
        if err != nil {
            grpcclient.reconnect <- true
            return
        }
    }
}

func (grpcclient *gRPCClient) waitUntilReady() bool {
    ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
    defer cancel()
    return grpcclient.conn.WaitForStateChange(ctx, connectivity.Ready)
}

Option 2: Using IsReconnected and Timer

Another approach is to use the IsReconnected method that repeatedly checks the connection state and reconnects if necessary:

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

    go grpcclient.process()
    for {
        select {
        case <-grpcclient.reconnect:
            // Check and reconnect
            if !grpcclient.isReconnected(1*time.Second, 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) isReconnected(check, timeout time.Duration) bool {
    ctx, cancel := context.WithTimeout(context.Background(), timeout)
    defer cancel()
    ticker := time.NewTicker(check)

    for {
        select {
        case <-ticker.C:
            grpcclient.conn.Connect()
            if grpcclient.conn.GetState() == connectivity.Ready {
                return true
            }
        case <-ctx.Done():
            return false
        }
    }
}

Conclusion

Using either of these methods, you can implement proper reconnection logic for your Go gRPC client, ensuring reliable communication even when server pods are recycled.

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