Agent drain: implement first half.

- Agent sends drain signal to Server.
- Server only logs it.

cmd/agent/app/server.go

@@ -24,10 +24,13 @@ import (
 	"net"
 	"net/http"
 	"net/http/pprof"
+	"os"
+	"os/signal"
 	"runtime"
 	runpprof "runtime/pprof"
 	"strconv"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus/promhttp"
@@ -49,8 +52,8 @@ func NewAgentCommand(a *Agent, o *options.GrpcProxyAgentOptions) *cobra.Command
 		Use:  "agent",
 		Long: `A gRPC agent, Connects to the proxy and then allows traffic to be forwarded to it.`,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			stopCh := make(chan struct{})
-			return a.Run(o, stopCh)
+			drainCh, stopCh := SetupSignalHandler()
+			return a.Run(o, drainCh, stopCh)
 		},
 	}
 
@@ -64,13 +67,13 @@ type Agent struct {
 	cs *agent.ClientSet
 }
 
-func (a *Agent) Run(o *options.GrpcProxyAgentOptions, stopCh <-chan struct{}) error {
+func (a *Agent) Run(o *options.GrpcProxyAgentOptions, drainCh, stopCh <-chan struct{}) error {
 	o.Print()
 	if err := o.Validate(); err != nil {
 		return fmt.Errorf("failed to validate agent options with %v", err)
 	}
 
-	cs, err := a.runProxyConnection(o, stopCh)
+	cs, err := a.runProxyConnection(o, drainCh, stopCh)
 	if err != nil {
 		return fmt.Errorf("failed to run proxy connection with %v", err)
 	}
@@ -92,7 +95,29 @@ func (a *Agent) Run(o *options.GrpcProxyAgentOptions, stopCh <-chan struct{}) er
 	return nil
 }
 
-func (a *Agent) runProxyConnection(o *options.GrpcProxyAgentOptions, stopCh <-chan struct{}) (*agent.ClientSet, error) {
+var shutdownSignals = []os.Signal{os.Interrupt, syscall.SIGTERM}
+
+func SetupSignalHandler() (drainCh, stopCh <-chan struct{}) {
+	drain := make(chan struct{})
+	stop := make(chan struct{})
+	c := make(chan os.Signal, 2)
+	signal.Notify(c, shutdownSignals...)
+	labels := runpprof.Labels(
+		"core", "signalHandler",
+	)
+	go runpprof.Do(context.Background(), labels, func(context.Context) { handleSignals(c, drain, stop) })
+
+	return drain, stop
+}
+
+func handleSignals(signalCh chan os.Signal, drainCh, stopCh chan struct{}) {
+	<-signalCh
+	close(drainCh)
+	<-signalCh
+	close(stopCh)
+}
+
+func (a *Agent) runProxyConnection(o *options.GrpcProxyAgentOptions, drainCh, stopCh <-chan struct{}) (*agent.ClientSet, error) {
 	var tlsConfig *tls.Config
 	var err error
 	if tlsConfig, err = util.GetClientTLSConfig(o.CaCert, o.AgentCert, o.AgentKey, o.ProxyServerHost, o.AlpnProtos); err != nil {
@@ -106,7 +131,7 @@ func (a *Agent) runProxyConnection(o *options.GrpcProxyAgentOptions, stopCh <-ch
 		}),
 	}
 	cc := o.ClientSetConfig(dialOptions...)
-	cs := cc.NewAgentClientSet(stopCh)
+	cs := cc.NewAgentClientSet(drainCh, stopCh)
 	cs.Serve()
 
 	return cs, nil

pkg/agent/client.go

@@ -137,7 +137,10 @@ type Client struct {
 	address string
 	opts    []grpc.DialOption
 	conn    *grpc.ClientConn
+
+	drainCh <-chan struct{}
 	stopCh  chan struct{}
+
 	// locks
 	sendLock      sync.Mutex
 	recvLock      sync.Mutex
@@ -158,6 +161,7 @@ func newAgentClient(address, agentID, agentIdentifiers string, cs *ClientSet, op
 		agentIdentifiers:        agentIdentifiers,
 		opts:                    opts,
 		probeInterval:           cs.probeInterval,
+		drainCh:                 cs.drainCh,
 		stopCh:                  make(chan struct{}),
 		serviceAccountTokenPath: cs.serviceAccountTokenPath,
 		connManager:             newConnectionManager(),
@@ -325,6 +329,17 @@ func (a *Client) Serve() {
 		case <-a.stopCh:
 			klog.V(2).InfoS("stop agent client.")
 			return
+		case <-a.drainCh:
+			klog.V(2).InfoS("drain agent client.")
+			drainPkt := &client.Packet{
+				Type: client.PacketType_DRAIN,
+				Payload: &client.Packet_Drain{
+					Drain: &client.Drain{},
+				},
+			}
+			if err := a.Send(drainPkt); err != nil {
+				klog.ErrorS(err, "drain failure", "")
+			}
 		default:
 		}
 

pkg/agent/clientset.go

@@ -52,6 +52,8 @@ type ClientSet struct {
 	dialOptions []grpc.DialOption
 	// file path contains service account token
 	serviceAccountTokenPath string
+	// channel to signal that the agent is pending termination.
+	drainCh <-chan struct{}
 	// channel to signal shutting down the client set. Primarily for test.
 	stopCh <-chan struct{}
 
@@ -141,7 +143,7 @@ type ClientSetConfig struct {
 	SyncForever             bool
 }
 
-func (cc *ClientSetConfig) NewAgentClientSet(stopCh <-chan struct{}) *ClientSet {
+func (cc *ClientSetConfig) NewAgentClientSet(drainCh, stopCh <-chan struct{}) *ClientSet {
 	return &ClientSet{
 		clients:                 make(map[string]*Client),
 		agentID:                 cc.AgentID,
@@ -154,6 +156,7 @@ func (cc *ClientSetConfig) NewAgentClientSet(stopCh <-chan struct{}) *ClientSet
 		serviceAccountTokenPath: cc.ServiceAccountTokenPath,
 		warnOnChannelLimit:      cc.WarnOnChannelLimit,
 		syncForever:             cc.SyncForever,
+		drainCh:                 drainCh,
 		stopCh:                  stopCh,
 	}
 }

pkg/server/server.go

@@ -990,6 +990,8 @@ func (s *ProxyServer) serveRecvBackend(backend Backend, agentID string, recvCh <
 				klog.V(5).InfoS("CLOSE_RSP sent to frontend", "connectionID", resp.ConnectID)
 			}
 
+		case client.PacketType_DRAIN:
+			klog.V(2).InfoS("agent is draining", "agentID", agentID)
 		default:
 			klog.V(5).InfoS("Ignoring unrecognized packet from backend", "packet", pkt, "agentID", agentID)
 		}

tests/framework/agent.go

@@ -27,6 +27,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"sync"
+	"syscall"
 	"testing"
 	"time"
 
@@ -53,6 +54,7 @@ type AgentRunner interface {
 type Agent interface {
 	GetConnectedServerCount() (int, error)
 	Ready() bool
+	Drain()
 	Stop()
 	Metrics() metricstest.AgentTester
 }
@@ -66,9 +68,10 @@ func (*InProcessAgentRunner) Start(t testing.TB, opts AgentOpts) (Agent, error)
 	}
 
 	ctx, cancel := context.WithCancel(context.Background())
+	drainCh := make(chan struct{})
 	stopCh := make(chan struct{})
 	go func() {
-		if err := a.Run(o, stopCh); err != nil {
+		if err := a.Run(o, drainCh, stopCh); err != nil {
 			log.Printf("ERROR running agent: %v", err)
 			cancel()
 		}
@@ -84,6 +87,7 @@ func (*InProcessAgentRunner) Start(t testing.TB, opts AgentOpts) (Agent, error)
 
 	pa := &inProcessAgent{
 		client:     a.ClientSet(),
+		drainCh:    drainCh,
 		stopCh:     stopCh,
 		healthAddr: healthAddr,
 	}
@@ -94,12 +98,21 @@ func (*InProcessAgentRunner) Start(t testing.TB, opts AgentOpts) (Agent, error)
 type inProcessAgent struct {
 	client *agent.ClientSet
 
+	drainOnce sync.Once
+	drainCh   chan struct{}
+
 	stopOnce sync.Once
 	stopCh   chan struct{}
 
 	healthAddr string
 }
 
+func (a *inProcessAgent) Drain() {
+	a.drainOnce.Do(func() {
+		close(a.drainCh)
+	})
+}
+
 func (a *inProcessAgent) Stop() {
 	a.stopOnce.Do(func() {
 		close(a.stopCh)
@@ -160,7 +173,16 @@ type externalAgent struct {
 	cmd                   *exec.Cmd
 	metrics               *metricstest.Tester
 
-	stopOnce sync.Once
+	drainOnce sync.Once
+	stopOnce  sync.Once
+}
+
+func (a *externalAgent) Drain() {
+	a.drainOnce.Do(func() {
+		if err := a.cmd.Process.Signal(syscall.SIGTERM); err != nil {
+			log.Fatalf("Error draining agent process: %v", err)
+		}
+	})
 }
 
 func (a *externalAgent) Stop() {