How to Handle gRPC Stream Disconnections During Kubernetes Pod Recycling?

How to Implement Resiliency for gRPC Client Reconnections

When establishing a gRPC client-server connection within a Kubernetes cluster, it's crucial to consider resiliency measures to handle pod recycling scenarios. By utilizing the capabilities of clientconn.go, you can automate the reconnection process for the RPC connection. However, managing the stream requires manual intervention.

Identifying the Stream Disconnection Issue

In case of pod recycling, the RPC connection will be automatically reconnected by clientconn.go. However, the stream remains disconnected, necessitating the establishment of a new stream.

Solution: Stream Management with Reattempt Mechanism

To address this issue, implement the following pseudo-code to wait for the RPC connection to enter a READY state and establish a new stream:

func (grpcclient *gRPCClient) ProcessRequests() error {
    defer grpcclient.Close()    
    
    go grpcclient.process()
    for {
      select {
        case <- grpcclient.reconnect:
           if !grpcclient.waitUntilReady() {
             return errors.New(&quot;failed to establish a connection within the defined timeout&quot;)
           }
           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(&quot;Request received&quot;)
        if err == io.EOF {          
            grpcclient.done <- true
            return
        }
        if err != nil {
            grpcclient.reconnect <- true
            return
            
        } else {
            //the happy path
            //code block to process any requests that are received
        }
    }
}

func (grpcclient *gRPCClient) waitUntilReady() bool {
  ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second) //define how long you want to wait for connection to be restored before giving up
  defer cancel()
  return grpcclient.conn.WaitForStateChange(ctx, conectivity.Ready)
}

Alternative Reconnection Strategy

A more accurate approach is to track the current connection state and manually reconnect using the Connect function:

func (grpcclient *gRPCClient) ProcessRequests() error {
        defer grpcclient.Close()    
        
        go grpcclient.process()
        for {
          select {
            case <- grpcclient.reconnect:
               if !grpcclient.isReconnected(1*time.Second, 60*time.Second) {
                 return errors.New(&quot;failed to establish a connection within the defined timeout&quot;)
               }
               go grpcclient.process()
            case <- grpcclient.done:
              return nil
          }
        }
}

func (grpcclient *gRPCClient) isReconnected(check, timeout time.Duration) bool {
  ctx, cancel := context.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
    }
  }
}

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