Heartbeat Automatic Reload (elastic#8023)

Add automatic reloading for heartbeat config files.

This deprecates the `watch.poll_file` options.

This patch also fixes a potential source of races in code using `cfgfile/Runner` by making that interface implement `Stringer`, the reason being that by default `cfgfile/Runner` can recursively print the backing structure, which can trigger a race.

CHANGELOG.asciidoc

@@ -136,6 +136,9 @@ https://github.com/elastic/beats/compare/v6.4.0...master[Check the HEAD diff]
 
 *Winlogbeat*
 
+*Heartbeat*
+
+- Add automatic config file reloading. {pull}8023[8023]
 
 ==== Deprecated
 
@@ -144,6 +147,7 @@ https://github.com/elastic/beats/compare/v6.4.0...master[Check the HEAD diff]
 *Filebeat*
 
 *Heartbeat*
+- watch.poll_file is now deprecated and superceded by automatic config file reloading.
 
 *Metricbeat*
 - Redis `info` `replication.master_offset` has been deprecated in favor of `replication.master.offset`.{pull}7695[7695]

heartbeat/_meta/beat.reference.yml

@@ -32,14 +32,6 @@ heartbeat.monitors:
   ipv6: true
   mode: any
 
-  # Configure file json file to be watched for changes to the monitor:
-  #watch.poll_file:
-    # Path to check for updates.
-    #path:
-
-    # Interval between file file changed checks.
-    #interval: 5s
-
   # Total running time per ping test.
   timeout: 16s
 
@@ -62,6 +54,15 @@ heartbeat.monitors:
   # sub-dictionary. Default is false.
   #fields_under_root: false
 
+  # NOTE: THIS FEATURE IS DEPRECATED AND WILL BE REMOVED IN A FUTURE RELEASE
+  # Configure file json file to be watched for changes to the monitor:
+  #watch.poll_file:
+    # Path to check for updates.
+    #path:
+
+    # Interval between file file changed checks.
+    #interval: 5s
+
 - type: tcp # monitor type `tcp`. Connect via TCP and optionally verify endpoint
             # by sending/receiving a custom payload
 
@@ -98,14 +99,6 @@ heartbeat.monitors:
   ipv6: true
   mode: any
 
-  # Configure file json file to be watched for changes to the monitor:
-  #watch.poll_file:
-    # Path to check for updates.
-    #path:
-
-    # Interval between file file changed checks.
-    #interval: 5s
-
   # List of ports to ping if host does not contain a port number
   # ports: [80, 9200, 5044]
 
@@ -135,6 +128,16 @@ heartbeat.monitors:
     # Required TLS protocols
     #supported_protocols: ["TLSv1.0", "TLSv1.1", "TLSv1.2"]
 
+  # NOTE: THIS FEATURE IS DEPRECATED AND WILL BE REMOVED IN A FUTURE RELEASE
+  # Configure file json file to be watched for changes to the monitor:
+  #watch.poll_file:
+    # Path to check for updates.
+    #path:
+
+    # Interval between file file changed checks.
+    #interval: 5s
+
+
 - type: http # monitor type `http`. Connect via HTTP an optionally verify response
 
   # Monitor name used for job name and document type
@@ -205,6 +208,16 @@ heartbeat.monitors:
     # Required response contents.
     #body:
 
+  # NOTE: THIS FEATURE IS DEPRECATED AND WILL BE REMOVED IN A FUTURE RELEASE
+  # Configure file json file to be watched for changes to the monitor:
+  #watch.poll_file:
+    # Path to check for updates.
+    #path:
+
+    # Interval between file file changed checks.
+    #interval: 5s
+
+
 heartbeat.scheduler:
   # Limit number of concurrent tasks executed by heartbeat. The task limit if
   # disabled if set to 0. The default is 0.

heartbeat/beater/heartbeat.go

@@ -21,33 +21,38 @@ import (
 	"fmt"
 	"time"
 
-	"github.com/elastic/beats/libbeat/beat"
-	"github.com/elastic/beats/libbeat/common"
-	"github.com/elastic/beats/libbeat/logp"
+	"github.com/pkg/errors"
 
 	"github.com/elastic/beats/heartbeat/config"
 	"github.com/elastic/beats/heartbeat/monitors"
 	"github.com/elastic/beats/heartbeat/scheduler"
+	"github.com/elastic/beats/libbeat/beat"
+	"github.com/elastic/beats/libbeat/cfgfile"
+	"github.com/elastic/beats/libbeat/common"
 	"github.com/elastic/beats/libbeat/common/cfgwarn"
+	"github.com/elastic/beats/libbeat/logp"
 )
 
+// Heartbeat represents the root datastructure of this beat.
 type Heartbeat struct {
 	done chan struct{}
-
-	scheduler *scheduler.Scheduler
-	manager   *monitorManager
+	// config is used for iterating over elements of the config.
+	config          config.Config
+	scheduler       *scheduler.Scheduler
+	monitorReloader *cfgfile.Reloader
 }
 
-func New(b *beat.Beat, cfg *common.Config) (beat.Beater, error) {
+// New creates a new heartbeat.
+func New(b *beat.Beat, rawConfig *common.Config) (beat.Beater, error) {
 	cfgwarn.Beta("Heartbeat is beta software")
 
-	config := config.DefaultConfig
-	if err := cfg.Unpack(&config); err != nil {
+	parsedConfig := config.DefaultConfig
+	if err := rawConfig.Unpack(&parsedConfig); err != nil {
 		return nil, fmt.Errorf("Error reading config file: %v", err)
 	}
 
-	limit := config.Scheduler.Limit
-	locationName := config.Scheduler.Location
+	limit := parsedConfig.Scheduler.Limit
+	locationName := parsedConfig.Scheduler.Location
 	if locationName == "" {
 		locationName = "Local"
 	}
@@ -56,36 +61,76 @@ func New(b *beat.Beat, cfg *common.Config) (beat.Beater, error) {
 		return nil, err
 	}
 
-	sched := scheduler.NewWithLocation(limit, location)
-	manager, err := newMonitorManager(b.Publisher, sched, monitors.Registry, config.Monitors)
-	if err != nil {
-		return nil, err
-	}
+	scheduler := scheduler.NewWithLocation(limit, location)
 
 	bt := &Heartbeat{
 		done:      make(chan struct{}),
-		scheduler: sched,
-		manager:   manager,
+		config:    parsedConfig,
+		scheduler: scheduler,
 	}
 	return bt, nil
 }
 
+// Run executes the beat.
 func (bt *Heartbeat) Run(b *beat.Beat) error {
 	logp.Info("heartbeat is running! Hit CTRL-C to stop it.")
 
+	err := bt.RunStaticMonitors(b)
+	if err != nil {
+		return err
+	}
+
+	if bt.config.ConfigMonitors.Enabled() {
+		bt.monitorReloader = cfgfile.NewReloader(b.Publisher, bt.config.ConfigMonitors)
+		defer bt.monitorReloader.Stop()
+
+		err := bt.RunDynamicMonitors(b)
+		if err != nil {
+			return err
+		}
+	}
+
 	if err := bt.scheduler.Start(); err != nil {
 		return err
 	}
 	defer bt.scheduler.Stop()
 
 	<-bt.done
 
-	bt.manager.Stop()
-
 	logp.Info("Shutting down.")
 	return nil
 }
 
+// RunStaticMonitors runs the `heartbeat.monitors` portion of the yaml config if present.
+func (bt *Heartbeat) RunStaticMonitors(b *beat.Beat) error {
+	factory := monitors.NewFactory(bt.scheduler, true)
+
+	for _, cfg := range bt.config.Monitors {
+		created, err := factory.Create(b.Publisher, cfg, nil)
+		if err != nil {
+			return errors.Wrap(err, "could not create monitor")
+		}
+		created.Start()
+	}
+	return nil
+}
+
+// RunDynamicMonitors runs the `heartbeat.config.monitors` portion of the yaml config if present.
+func (bt *Heartbeat) RunDynamicMonitors(b *beat.Beat) (err error) {
+	factory := monitors.NewFactory(bt.scheduler, false)
+
+	// Check monitor configs
+	if err := bt.monitorReloader.Check(factory); err != nil {
+		return err
+	}
+
+	// Execute the monitor
+	go bt.monitorReloader.Run(factory)
+
+	return nil
+}
+
+// Stop stops the beat.
 func (bt *Heartbeat) Stop() {
 	close(bt.done)
 }