Allow using a remote MistUtilLoad for load balancing (#1329)

We want to allow running catalyst-api separately to catalyst, so MistUtilLoad needs to be accessed remotely.

balancer/mist/mist_balancer.go

@@ -25,30 +25,42 @@ var mistUtilLoadSingleRequestTimeout = 15 * time.Second
 var mistUtilLoadLoopTimeout = 2 * time.Minute
 
 type MistBalancer struct {
+	isLocal  bool
 	config   *balancer.Config
-	cmd      *exec.Cmd
 	endpoint string
 	// Blocks until initial startup
 	startupOnce  sync.Once
 	startupError error
 }
 
-// create a new load balancer instance
-func NewBalancer(config *balancer.Config) balancer.Balancer {
+// NewLocalBalancer creates a new local MistUtilLoad instance
+func NewLocalBalancer(config *balancer.Config) balancer.Balancer {
 	_, err := exec.LookPath("MistUtilLoad")
 	if err != nil {
 		glog.Warning("MistUtilLoad not found, not doing meaningful balancing")
 		return &balancer.BalancerStub{}
 	}
 	return &MistBalancer{
+		isLocal:  true,
 		config:   config,
-		cmd:      nil,
 		endpoint: fmt.Sprintf("http://127.0.0.1:%d", config.MistUtilLoadPort),
 	}
 }
 
+// NewRemoteBalancer creates a new remote MistUtilLoad instance
+func NewRemoteBalancer(config *balancer.Config) balancer.Balancer {
+	return &MistBalancer{
+		config:   config,
+		endpoint: fmt.Sprintf("http://%s:%d", config.MistHost, config.MistUtilLoadPort),
+	}
+}
+
 // start this load balancer instance, execing MistUtilLoad if necessary
 func (b *MistBalancer) Start(ctx context.Context) error {
+	if !b.isLocal {
+		// remote load balancer instance is not managed by catalyst-api
+		return nil
+	}
 	b.killPreviousBalancer(ctx)
 
 	go func() {
@@ -288,17 +300,17 @@ func (b *MistBalancer) isBalancerRunning(ctx context.Context) bool {
 func (b *MistBalancer) execBalancer(ctx context.Context, balancerArgs []string) error {
 	args := append(balancerArgs, "-p", fmt.Sprintf("%d", b.config.MistUtilLoadPort), "-g", "4")
 	glog.Infof("Running MistUtilLoad with %v", args)
-	b.cmd = exec.CommandContext(ctx, "MistUtilLoad", args...)
+	cmd := exec.CommandContext(ctx, "MistUtilLoad", args...)
 
-	b.cmd.Stdout = os.Stdout
-	b.cmd.Stderr = os.Stderr
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
 
-	err := b.cmd.Start()
+	err := cmd.Start()
 	if err != nil {
 		return err
 	}
 
-	err = b.cmd.Wait()
+	err = cmd.Wait()
 	if err != nil {
 		return err
 	}

balancer/mist/mist_balancer_test.go

@@ -31,7 +31,6 @@ func start(t *testing.T) (*MistBalancer, *mockMistUtilLoad) {
 			OwnRegion:          "fra",
 			OwnRegionTagAdjust: 1000,
 		},
-		cmd:      nil,
 		endpoint: mul.Server.URL,
 	}
 	// Mock startup loop

main.go

@@ -275,7 +275,7 @@ func main() {
 	c := cluster.NewCluster(&cli)
 
 	// Start balancer
-	mistBalancer := mist_balancer.NewBalancer(&balancer.Config{
+	mistBalancerConfig := &balancer.Config{
 		Args:                     cli.BalancerArgs,
 		MistUtilLoadPort:         uint32(cli.MistLoadBalancerPort),
 		MistLoadBalancerTemplate: cli.MistLoadBalancerTemplate,
@@ -284,7 +284,8 @@ func main() {
 		NodeName:                 cli.NodeName,
 		OwnRegion:                cli.OwnRegion,
 		OwnRegionTagAdjust:       cli.OwnRegionTagAdjust,
-	})
+	}
+	mistBalancer := mist_balancer.NewLocalBalancer(mistBalancerConfig)
 
 	bal := mistBalancer
 	if balancer.CombinedBalancerEnabled(cli.CataBalancer) {