From d56b5de5dcf99b662040b2046a42eae58be2da5d Mon Sep 17 00:00:00 2001
From: Zhonghu Xu <xuzhonghu@huawei.com>
Date: Mon, 17 Feb 2020 15:21:41 +0800
Subject: [PATCH] Backoff retry mcp client (#20114)

* use backoff to reconnect to mcp server

* fix race

* fix ayj's comment
---
 pkg/mcp/sink/client_sink.go | 37 +++++++++++++++++++------------------
 pkg/mcp/sink/sink.go        |  2 +-
 2 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/pkg/mcp/sink/client_sink.go b/pkg/mcp/sink/client_sink.go
index 9f13b8fa1d95..784b578ef23c 100644
--- a/pkg/mcp/sink/client_sink.go
+++ b/pkg/mcp/sink/client_sink.go
@@ -19,10 +19,11 @@ import (
 	"io"
 	"time"
 
-	"istio.io/istio/pkg/mcp/status"
+	"github.com/cenkalti/backoff"
 
 	mcp "istio.io/api/mcp/v1alpha1"
-	"istio.io/istio/pkg/mcp/monitoring"
+
+	"istio.io/istio/pkg/mcp/status"
 )
 
 var (
@@ -33,43 +34,40 @@ var (
 // Client implements the client for the MCP source service. The client is the
 // sink and receives configuration from the server.
 type Client struct {
-	// Client receives configuration using the ResourceSource RPC service
-	stream mcp.ResourceSource_EstablishResourceStreamClient
-
 	client mcp.ResourceSourceClient
 	*Sink
-	reporter monitoring.Reporter
 }
 
 // NewClient returns a new instance of Client.
 func NewClient(client mcp.ResourceSourceClient, options *Options) *Client {
 	return &Client{
-		Sink:     New(options),
-		reporter: options.Reporter,
-		client:   client,
+		Sink:   New(options),
+		client: client,
 	}
 }
 
 var reconnectTestProbe = func() {}
 
 func (c *Client) Run(ctx context.Context) {
-	// The first attempt is immediate.
-	retryDelay := time.Nanosecond
+	var err error
+	var stream Stream
 
 	for {
+		backoffPolicy := backoff.NewExponentialBackOff()
+		backoffPolicy.InitialInterval = time.Nanosecond
+		backoffPolicy.MaxElapsedTime = 0
+		t := backoff.NewTicker(backoffPolicy)
 		// connect w/retry
 		for {
 			select {
 			case <-ctx.Done():
+				t.Stop()
 				return
-			case <-time.After(retryDelay):
+			case <-t.C:
 			}
 
-			// slow subsequent reconnection attempts down
-			retryDelay = reestablishStreamDelay
-
 			scope.Info("(re)trying to establish new MCP sink stream")
-			stream, err := c.client.EstablishResourceStream(ctx)
+			stream, err = c.client.EstablishResourceStream(ctx)
 
 			if reconnectTestProbe != nil {
 				reconnectTestProbe()
@@ -78,17 +76,20 @@ func (c *Client) Run(ctx context.Context) {
 			if err == nil {
 				c.reporter.RecordStreamCreateSuccess()
 				scope.Info("New MCP sink stream created")
-				c.stream = stream
 				break
 			}
 
 			scope.Errorf("Failed to create a new MCP sink stream: %v", err)
 		}
 
-		err := c.ProcessStream(c.stream)
+		// stop the ticker
+		t.Stop()
+
+		err := c.ProcessStream(stream)
 		if err != nil && err != io.EOF {
 			c.reporter.RecordRecvError(err, status.Code(err))
 			scope.Errorf("Error receiving MCP response: %v", err)
 		}
 	}
+
 }
diff --git a/pkg/mcp/sink/sink.go b/pkg/mcp/sink/sink.go
index 8085a6d86e85..959a22ca20d4 100644
--- a/pkg/mcp/sink/sink.go
+++ b/pkg/mcp/sink/sink.go
@@ -54,7 +54,7 @@ type Sink struct {
 }
 
 // New creates a new resource sink.
-func New(options *Options) *Sink { // nolint: lll
+func New(options *Options) *Sink {
 	nodeInfo := &mcp.SinkNode{
 		Id:          options.ID,
 		Annotations: options.Metadata,