command: add '-monitor' flag to node drain

CHANGELOG.md

@@ -14,6 +14,8 @@ IMPROVEMENTS:
    isolate canary instances during deployments [[GH-4259](https://github.com/hashicorp/nomad/issues/4259)]
  * core: Emit Node events for drain and eligibility operations as well as for
    missed heartbeats [[GH-4284](https://github.com/hashicorp/nomad/issues/4284)], [[GH-4291](https://github.com/hashicorp/nomad/issues/4291)], [[GH-4292](https://github.com/hashicorp/nomad/issues/4292)]
+ * cli: Add node drain monitoring with new `-monitor` flag on node drain
+   command [[GH-4260](https://github.com/hashicorp/nomad/issues/4260)]
  * cli: Add node drain details to node status [[GH-4247](https://github.com/hashicorp/nomad/issues/4247)]
  * client: Avoid splitting log line across two files [[GH-4282](https://github.com/hashicorp/nomad/issues/4282)]
  * command: Add -short option to init command that emits a minimal

api/nodes.go

@@ -193,6 +193,7 @@ func (n *Nodes) monitorDrainNode(ctx context.Context, nodeID string, index uint6
 	defer close(nodeCh)
 
 	var lastStrategy *DrainStrategy
+	var strategyChanged bool
 	q := QueryOptions{
 		AllowStale: true,
 		WaitIndex:  index,
@@ -209,7 +210,12 @@ func (n *Nodes) monitorDrainNode(ctx context.Context, nodeID string, index uint6
 		}
 
 		if node.DrainStrategy == nil {
-			msg := Messagef(MonitorMsgLevelInfo, "Node %q has marked all allocations for migration", nodeID)
+			var msg *MonitorMessage
+			if strategyChanged {
+				msg = Messagef(MonitorMsgLevelInfo, "Node %q has marked all allocations for migration", nodeID)
+			} else {
+				msg = Messagef(MonitorMsgLevelInfo, "No drain strategy set for node %s", nodeID)
+			}
 			select {
 			case nodeCh <- msg:
 			case <-ctx.Done():
@@ -236,6 +242,7 @@ func (n *Nodes) monitorDrainNode(ctx context.Context, nodeID string, index uint6
 		}
 
 		lastStrategy = node.DrainStrategy
+		strategyChanged = true
 
 		// Drain still ongoing, update index and block for updates
 		q.WaitIndex = meta.LastIndex

command/node_drain.go

@@ -49,6 +49,9 @@ Node Drain Options:
   -detach
     Return immediately instead of entering monitor mode.
 
+  -monitor
+    Enter monitor mode directly without modifying the drain status.
+
   -force
     Force remove allocations off the node immediately.
 
@@ -113,7 +116,8 @@ func (c *NodeDrainCommand) Name() string { return "node-drain" }
 
 func (c *NodeDrainCommand) Run(args []string) int {
 	var enable, disable, detach, force,
-		noDeadline, ignoreSystem, keepIneligible, self, autoYes bool
+		noDeadline, ignoreSystem, keepIneligible,
+		self, autoYes, monitor bool
 	var deadline string
 
 	flags := c.Meta.FlagSet(c.Name(), FlagSetClient)
@@ -128,14 +132,22 @@ func (c *NodeDrainCommand) Run(args []string) int {
 	flags.BoolVar(&keepIneligible, "keep-ineligible", false, "Do not update the nodes scheduling eligibility")
 	flags.BoolVar(&self, "self", false, "")
 	flags.BoolVar(&autoYes, "yes", false, "Automatic yes to prompts.")
+	flags.BoolVar(&monitor, "monitor", false, "Monitor drain status.")
 
 	if err := flags.Parse(args); err != nil {
 		return 1
 	}
 
+	// Check that enable or disable is not set with monitor
+	if monitor && (enable || disable) {
+		c.Ui.Error("The -monitor flag cannot be used with the '-enable' or '-disable' flags")
+		c.Ui.Error(commandErrorText(c))
+		return 1
+	}
+
 	// Check that we got either enable or disable, but not both.
-	if (enable && disable) || (!enable && !disable) {
-		c.Ui.Error("Ethier the '-enable' or '-disable' flag must be set")
+	if (enable && disable) || (!monitor && !enable && !disable) {
+		c.Ui.Error("Ethier the '-enable' or '-disable' flag must be set, unless using '-monitor'")
 		c.Ui.Error(commandErrorText(c))
 		return 1
 	}
@@ -236,6 +248,13 @@ func (c *NodeDrainCommand) Run(args []string) int {
 		return 1
 	}
 
+	// If monitoring the drain start the montior and return when done
+	if monitor {
+		c.Ui.Info(fmt.Sprintf("%s: Monitoring node %q: Ctrl-C to detach monitoring", formatTime(time.Now()), node.ID))
+		c.monitorDrain(client, context.Background(), node, 0, ignoreSystem)
+		return 0
+	}
+
 	// Confirm drain if the node was a prefix match.
 	if nodeID != node.ID && !autoYes {
 		verb := "enable"
@@ -290,20 +309,23 @@ func (c *NodeDrainCommand) Run(args []string) int {
 		now := time.Now()
 		c.Ui.Info(fmt.Sprintf("%s: Ctrl-C to stop monitoring: will not cancel the node drain", formatTime(now)))
 		c.Ui.Output(fmt.Sprintf("%s: Node %q drain strategy set", formatTime(now), node.ID))
-		outCh := client.Nodes().MonitorDrain(context.Background(), node.ID, meta.LastIndex, ignoreSystem)
-		for msg := range outCh {
-			switch msg.Level {
-			case api.MonitorMsgLevelInfo:
-				c.Ui.Info(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
-			case api.MonitorMsgLevelWarn:
-				c.Ui.Warn(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
-			case api.MonitorMsgLevelError:
-				c.Ui.Error(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
-			default:
-				c.Ui.Output(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
-			}
-		}
+		c.monitorDrain(client, context.Background(), node, meta.LastIndex, ignoreSystem)
 	}
-
 	return 0
 }
+
+func (c *NodeDrainCommand) monitorDrain(client *api.Client, ctx context.Context, node *api.Node, index uint64, ignoreSystem bool) {
+	outCh := client.Nodes().MonitorDrain(ctx, node.ID, index, ignoreSystem)
+	for msg := range outCh {
+		switch msg.Level {
+		case api.MonitorMsgLevelInfo:
+			c.Ui.Info(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
+		case api.MonitorMsgLevelWarn:
+			c.Ui.Warn(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
+		case api.MonitorMsgLevelError:
+			c.Ui.Error(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
+		default:
+			c.Ui.Output(fmt.Sprintf("%s: %s", formatTime(time.Now()), msg))
+		}
+	}
+}

command/node_drain_test.go

@@ -237,6 +237,19 @@ func TestNodeDrainCommand_Monitor(t *testing.T) {
 	if !strings.HasSuffix(out, expected) {
 		t.Fatalf("expected output to end with:\n%s", expected)
 	}
+
+	// Test -monitor flag
+	outBuf.Reset()
+	args = []string{"-address=" + url, "-self", "-monitor", "-ignore-system"}
+	t.Logf("Running: %v", args)
+	if code := cmd.Run(args); code != 0 {
+		t.Fatalf("expected exit 0, got: %d\n%s", code, outBuf.String())
+	}
+
+	out = outBuf.String()
+	t.Logf("Output:\n%s", out)
+
+	require.Contains(out, "No drain strategy set")
 }
 
 func TestNodeDrainCommand_Fails(t *testing.T) {

website/source/docs/commands/node/drain.html.md.erb

@@ -57,6 +57,7 @@ operation is desired.
   node. Remaining allocations after the deadline are force removed from the
   node. Defaults to 1 hour.
 * `-detach`: Return immediately instead of entering monitor mode.
+* `-monitor`: Enter monitor mode directly without modifying the drain status.
 * `-force`: Force remove allocations off the node immediately.
 * `-no-deadline`: No deadline allows the allocations to drain off the node
   without being force stopped after a certain deadline.
@@ -114,6 +115,14 @@ $ nomad node drain -disable -keep-ineligible 4d2ba53b
 ...
 ```
 
+Enable drain mode and detach from monitoring, then reattach later:
+
+```
+$ nomad node drain -enable -detach -self
+...
+$ nomad node drain -self -monitor
+...
+```
 
 [eligibility]: /docs/commands/node/eligibility.html
 [migrate]: /docs/job-specification/migrate.html