<p>I have a Go gRPC client connected to a gRPC server running in a different pod in my k8s cluster.</p>
<p>It's working well, receiving and processing requests.</p>
<p>I am now wondering how best to implement resiliency in the event that the gRPC server pod gets recycled.</p>
<p>As far as I can ascertain, the clientconn.go code should handle the reconnection automatically, but I just cannot get it to work and I fear my implementation is incorrect in the first instance.</p>
<p>Calling code from main:</p>
<pre><code>go func() {     
        if err := gRPCClient.ProcessRequests(); err != nil {
            log.Error(&quot;Error while processing Requests&quot;)
            //do something here??
        }
    }()
</code></pre>
<p>My code in the gRPCClient wrapper module:</p>
<pre><code>func (grpcclient *gRPCClient) ProcessRequests() error {
    defer grpcclient.Close()    

    for {
        request, err := reqclient.stream.Recv()
        log.Info(&quot;Request received&quot;)
        if err == io.EOF {          
            break
        }
        if err != nil {
            //when pod is recycled, this is what's hit with err:
            //rpc error: code = Unavailable desc = transport is closing&quot;

            //what is the correct pattern for recovery here so that we can await connection
            //and continue processing requests once more?
            //should I return err here and somehow restart the ProcessRequests() go routine in the 
            //main funcition?
            break
            
        } else {
            //the happy path
            //code block to process any requests that are received
        }
    }

    return nil
}

func (reqclient *RequestClient) Close() {
//this is called soon after the conneciton drops
        reqclient.conn.Close()
}
</code></pre>
<p>EDIT:
Emin Laletovic answered my question elegantly below and gets it most of the way there.
I had to make a few changes to the waitUntilReady function:</p>
<pre><code>func (grpcclient *gRPCClient) waitUntilReady() bool {
ctx, cancel := context.WithTimeout(context.Background(), 300*time.Second) //define how long you want to wait for connection to be restored before giving up
defer cancel()

currentState := grpcclient.conn.GetState()
stillConnecting := true

for currentState != connectivity.Ready &amp;&amp; stillConnecting {
    //will return true when state has changed from thisState, false if timeout
    stillConnecting = grpcclient.conn.WaitForStateChange(ctx, currentState)
    currentState = grpcclient.conn.GetState()
    log.WithFields(log.Fields{&quot;state: &quot;: currentState, &quot;timeout&quot;: timeoutDuration}).Info(&quot;Attempting reconnection. State has changed to:&quot;)
}

if stillConnecting == false {
    log.Error(&quot;Connection attempt has timed out.&quot;)
    return false
}

return true
}
</code></pre>

<p>The RPC connection is being handled automatically by <code>clientconn.go</code>, but that doesn't mean the stream is also automatically handled.</p>
<p>The stream, once broken, whether by the RPC connection breaking down or some other reason, cannot reconnect automatically, and you need to get a new stream from the server once the RPC connection is back up.</p>
<p>The pseudo-code for waiting the RPC connection to be in the <code>READY</code> state and establishing a new stream might look something like this:</p>
<pre><code>func (grpcclient *gRPCClient) ProcessRequests() error {
    defer grpcclient.Close()    
    
    go grpcclient.process()
    for {
      select {
        case &lt;- grpcclient.reconnect:
           if !grpcclient.waitUntilReady() {
             return errors.New(&quot;failed to establish a connection within the defined timeout&quot;)
           }
           go grpcclient.process()
        case &lt;- 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 &lt;- true
            return
        }
        if err != nil {
            grpcclient.reconnect &lt;- 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)
}
</code></pre>
<p><strong>EDIT:</strong></p>
<p>Revisiting the code above, a couple of mistakes should be corrected. The <code>WaitForStateChange</code> function waits for the connection state to change from the passed state, it doesn't wait for the connection to change into the passed state.</p>
<p>It is better to track the current state of the connection and use the <code>Connect</code> function to connect if the channel is idle.</p>
<pre><code>func (grpcclient *gRPCClient) ProcessRequests() error {
        defer grpcclient.Close()    
        
        go grpcclient.process()
        for {
          select {
            case &lt;- 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 &lt;- 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 &lt;- ticker.C:
        grpcclient.conn.Connect()
 
        if grpcclient.conn.GetState() == connectivity.Ready {
          return true
        }
      case &lt;- ctx.Done():
         return false
    }
  }
}
</code></pre>
