Improve monitoring reporter (#8090)

Add backoff and failover support to the Elasticsearch monitoring
reporter.
The monitoring reporter runs in 2 phases. First phase it checks for
monitoring being enabled in Elasticsearch. The check runs every 30s.
If multiple hosts are configured, one host is selected by random.
Once phase 1 succeeds, phase 2 (collection phase) is started.

Before this change, phase 2 was configured to use load-balancing without
timeout if multiple hosts are configured. With events being dropped on
error and only one document being generated every 10s, this was ok in
most cases. Still, if one output is blocked, waiting for a long timeout
failover to another host can happen, even if no error occured yet.
If the failover host has errors, it might end up in a tight
reconnect-loop without any backoff behavior.
With recent changes to 6.4 beats creates a many more documents, which
was not taken into account in original design. Due to this misbehaving
monitoring outputs are much more likely:
=> Problems with reporter
1. Failover was not handled correctly
2. Creating more then one event and potentially spurious errors raise the need for backoff

This changes configures the clients to failover mode only. Whenever the
connection to one host fails, another host is selected by random.
On failure the reporters output will backoff exponentially. If the second client
(after failover) also fails, then the backoff waiting times are doubled.
And so on.

(cherry picked from commit 43ee7d7)

CHANGELOG.asciidoc

@@ -40,6 +40,7 @@ https://github.com/elastic/beats/compare/v6.4.0...6.4[Check the HEAD diff]
 - Remove unix-like permission checks on Windows, so files can be opened. {issue}7849[7849]
 - Deregister pipeline loader callback when inputsRunner is stopped. {pull}7893[7893]
 - Replace index patterns in TSVB visualizations. {pull}7929[7929]
+- Add backoff support to x-pack monitoring outputs. {issue}7966[7966]
 
 *Auditbeat*
 

auditbeat/auditbeat.reference.yml

@@ -1143,6 +1143,17 @@ logging.files:
   # The default is 50.
   #bulk_max_size: 50
 
+  # The number of seconds to wait before trying to reconnect to Elasticsearch
+  # after a network error. After waiting backoff.init seconds, the Beat
+  # tries to reconnect. If the attempt fails, the backoff timer is increased
+  # exponentially up to backoff.max. After a successful connection, the backoff
+  # timer is reset. The default is 1s.
+  #backoff.init: 1s
+
+  # The maximum number of seconds to wait before attempting to connect to
+  # Elasticsearch after a network error. The default is 60s.
+  #backoff.max: 60s
+
   # Configure http request timeout before failing an request to Elasticsearch.
   #timeout: 90
 

filebeat/filebeat.reference.yml

@@ -1803,6 +1803,17 @@ logging.files:
   # The default is 50.
   #bulk_max_size: 50
 
+  # The number of seconds to wait before trying to reconnect to Elasticsearch
+  # after a network error. After waiting backoff.init seconds, the Beat
+  # tries to reconnect. If the attempt fails, the backoff timer is increased
+  # exponentially up to backoff.max. After a successful connection, the backoff
+  # timer is reset. The default is 1s.
+  #backoff.init: 1s
+
+  # The maximum number of seconds to wait before attempting to connect to
+  # Elasticsearch after a network error. The default is 60s.
+  #backoff.max: 60s
+
   # Configure http request timeout before failing an request to Elasticsearch.
   #timeout: 90
 

heartbeat/heartbeat.reference.yml

@@ -1250,6 +1250,17 @@ logging.files:
   # The default is 50.
   #bulk_max_size: 50
 
+  # The number of seconds to wait before trying to reconnect to Elasticsearch
+  # after a network error. After waiting backoff.init seconds, the Beat
+  # tries to reconnect. If the attempt fails, the backoff timer is increased
+  # exponentially up to backoff.max. After a successful connection, the backoff
+  # timer is reset. The default is 1s.
+  #backoff.init: 1s
+
+  # The maximum number of seconds to wait before attempting to connect to
+  # Elasticsearch after a network error. The default is 60s.
+  #backoff.max: 60s
+
   # Configure http request timeout before failing an request to Elasticsearch.
   #timeout: 90
 

libbeat/_meta/config.reference.yml

@@ -1036,6 +1036,17 @@ logging.files:
   # The default is 50.
   #bulk_max_size: 50
 
+  # The number of seconds to wait before trying to reconnect to Elasticsearch
+  # after a network error. After waiting backoff.init seconds, the Beat
+  # tries to reconnect. If the attempt fails, the backoff timer is increased
+  # exponentially up to backoff.max. After a successful connection, the backoff
+  # timer is reset. The default is 1s.
+  #backoff.init: 1s
+
+  # The maximum number of seconds to wait before attempting to connect to
+  # Elasticsearch after a network error. The default is 60s.
+  #backoff.max: 60s
+
   # Configure http request timeout before failing an request to Elasticsearch.
   #timeout: 90
 

libbeat/docs/monitoring/shared-monitor-config.asciidoc

@@ -39,6 +39,21 @@ configuration option contains the following fields:
 The maximum number of metrics to bulk in a single {es} bulk API index request.
 The default is `50`. For more information, see <<elasticsearch-output>>.
 
+[float]
+==== `backoff.init`
+
+The number of seconds to wait before trying to reconnect to Elasticsearch after
+a network error. After waiting `backoff.init` seconds, {beatname_uc} tries to
+reconnect. If the attempt fails, the backoff timer is increased exponentially up
+to `backoff.max`. After a successful connection, the backoff timer is reset. The
+default is 1s.
+
+[float]
+===== `backoff.max`
+
+The maximum number of seconds to wait before attempting to connect to
+Elasticsearch after a network error. The default is 60s.
+
 [float]
 ==== `compression_level`
 
@@ -79,10 +94,17 @@ The password that {beatname_uc} uses to authenticate with the {es} instances for
 shipping monitoring data.
 
 [float]
-==== `period`
+==== `metrics.period`
 
 The time interval (in seconds) when metrics are sent to the {es} cluster. A new
 snapshot of {beatname_uc} metrics is generated and scheduled for publishing each
+period. The default value is 10 * time.Second.
+
+[float]
+==== `state.period`
+
+The time interval (in seconds) when state information are sent to the {es} cluster. A new
+snapshot of {beatname_uc} state is generated and scheduled for publishing each
 period. The default value is 60 * time.Second.
 
 [float]

libbeat/monitoring/report/elasticsearch/config.go

@@ -42,6 +42,12 @@ type config struct {
 	BulkMaxSize      int               `config:"bulk_max_size" validate:"min=0"`
 	BufferSize       int               `config:"buffer_size"`
 	Tags             []string          `config:"tags"`
+	Backoff          backoff           `config:"backoff"`
+}
+
+type backoff struct {
+	Init time.Duration
+	Max  time.Duration
 }
 
 var defaultConfig = config{
@@ -61,4 +67,8 @@ var defaultConfig = config{
 	BulkMaxSize:      50,
 	BufferSize:       50,
 	Tags:             nil,
+	Backoff: backoff{
+		Init: 1 * time.Second,
+		Max:  60 * time.Second,
+	},
 }

libbeat/monitoring/report/elasticsearch/elasticsearch.go

@@ -54,7 +54,8 @@ type reporter struct {
 	// pipeline
 	pipeline *pipeline.Pipeline
 	client   beat.Client
-	out      outputs.Group
+
+	out []outputs.NetworkClient
 }
 
 var debugf = logp.MakeDebug("monitoring")
@@ -104,22 +105,21 @@ func makeReporter(beat beat.Info, cfg *common.Config) (report.Reporter, error) {
 		params[k] = v
 	}
 
-	out := outputs.Group{
-		Clients:   nil,
-		BatchSize: windowSize,
-		Retry:     0, // no retry. on error drop events
-	}
-
 	hosts, err := outputs.ReadHostList(cfg)
 	if err != nil {
 		return nil, err
 	}
+	if len(hosts) == 0 {
+		return nil, errors.New("empty hosts list")
+	}
+
+	var clients []outputs.NetworkClient
 	for _, host := range hosts {
 		client, err := makeClient(host, params, proxyURL, tlsConfig, &config)
 		if err != nil {
 			return nil, err
 		}
-		out.Clients = append(out.Clients, client)
+		clients = append(clients, client)
 	}
 
 	queueFactory := func(e queue.Eventer) (queue.Queue, error) {
@@ -131,18 +131,27 @@ func makeReporter(beat beat.Info, cfg *common.Config) (report.Reporter, error) {
 
 	monitoring := monitoring.Default.GetRegistry("xpack.monitoring")
 
+	outClient := outputs.NewFailoverClient(clients)
+	outClient = outputs.WithBackoff(outClient, config.Backoff.Init, config.Backoff.Max)
+
 	pipeline, err := pipeline.New(
 		beat,
 		monitoring,
-		queueFactory, out, pipeline.Settings{
+		queueFactory,
+		outputs.Group{
+			Clients:   []outputs.Client{outClient},
+			BatchSize: windowSize,
+			Retry:     0, // no retry. Drop event on error.
+		},
+		pipeline.Settings{
 			WaitClose:     0,
 			WaitCloseMode: pipeline.NoWaitOnClose,
 		})
 	if err != nil {
 		return nil, err
 	}
 
-	client, err := pipeline.Connect()
+	pipeConn, err := pipeline.Connect()
 	if err != nil {
 		pipeline.Close()
 		return nil, err
@@ -154,8 +163,8 @@ func makeReporter(beat beat.Info, cfg *common.Config) (report.Reporter, error) {
 		tags:       config.Tags,
 		checkRetry: checkRetry,
 		pipeline:   pipeline,
-		client:     client,
-		out:        out,
+		client:     pipeConn,
+		out:        clients,
 	}
 	go r.initLoop(config)
 	return r, nil
@@ -175,7 +184,7 @@ func (r *reporter) initLoop(c config) {
 
 	for {
 		// Select one configured endpoint by random and check if xpack is available
-		client := r.out.Clients[rand.Intn(len(r.out.Clients))].(outputs.NetworkClient)
+		client := r.out[rand.Intn(len(r.out))]
 		err := client.Connect()
 		if err == nil {
 			closing(client)

metricbeat/metricbeat.reference.yml

@@ -1710,6 +1710,17 @@ logging.files:
   # The default is 50.
   #bulk_max_size: 50
 
+  # The number of seconds to wait before trying to reconnect to Elasticsearch
+  # after a network error. After waiting backoff.init seconds, the Beat
+  # tries to reconnect. If the attempt fails, the backoff timer is increased
+  # exponentially up to backoff.max. After a successful connection, the backoff
+  # timer is reset. The default is 1s.
+  #backoff.init: 1s
+
+  # The maximum number of seconds to wait before attempting to connect to
+  # Elasticsearch after a network error. The default is 60s.
+  #backoff.max: 60s
+
   # Configure http request timeout before failing an request to Elasticsearch.
   #timeout: 90
 

packetbeat/packetbeat.reference.yml

@@ -1513,6 +1513,17 @@ logging.files:
   # The default is 50.
   #bulk_max_size: 50
 
+  # The number of seconds to wait before trying to reconnect to Elasticsearch
+  # after a network error. After waiting backoff.init seconds, the Beat
+  # tries to reconnect. If the attempt fails, the backoff timer is increased
+  # exponentially up to backoff.max. After a successful connection, the backoff
+  # timer is reset. The default is 1s.
+  #backoff.init: 1s
+
+  # The maximum number of seconds to wait before attempting to connect to
+  # Elasticsearch after a network error. The default is 60s.
+  #backoff.max: 60s
+
   # Configure http request timeout before failing an request to Elasticsearch.
   #timeout: 90
 

winlogbeat/winlogbeat.reference.yml

@@ -1065,6 +1065,17 @@ logging.files:
   # The default is 50.
   #bulk_max_size: 50
 
+  # The number of seconds to wait before trying to reconnect to Elasticsearch
+  # after a network error. After waiting backoff.init seconds, the Beat
+  # tries to reconnect. If the attempt fails, the backoff timer is increased
+  # exponentially up to backoff.max. After a successful connection, the backoff
+  # timer is reset. The default is 1s.
+  #backoff.init: 1s
+
+  # The maximum number of seconds to wait before attempting to connect to
+  # Elasticsearch after a network error. The default is 60s.
+  #backoff.max: 60s
+
   # Configure http request timeout before failing an request to Elasticsearch.
   #timeout: 90