agent: suppose filter_default telemetry option

command/agent/command.go

@@ -888,6 +888,10 @@ func (c *Command) setupTelemetry(config *Config) (*metrics.InmemSink, error) {
 	metricsConf.AllowedPrefixes = allowedPrefixes
 	metricsConf.BlockedPrefixes = blockedPrefixes
 
+	if telConfig.FilterDefault != nil {
+		metricsConf.FilterDefault = *telConfig.FilterDefault
+	}
+
 	// Configure the statsite sink
 	var fanout metrics.FanoutSink
 	if telConfig.StatsiteAddr != "" {

command/agent/config.go

@@ -444,6 +444,10 @@ type Telemetry struct {
 	// PrefixFilter allows for filtering out metrics from being collected
 	PrefixFilter []string `mapstructure:"prefix_filter"`
 
+	// FilterDefault controls whether to allow metrics that have not been specified
+	// by the filter
+	FilterDefault *bool `mapstructure:"filter_default"`
+
 	// DisableDispatchedJobSummaryMetrics allows for ignore dispatched jobs when
 	// publishing Job summary metrics. This is useful in environment that produce
 	// high numbers of single count dispatch jobs as the metrics for each take up
@@ -1320,6 +1324,10 @@ func (a *Telemetry) Merge(b *Telemetry) *Telemetry {
 		result.PrefixFilter = b.PrefixFilter
 	}
 
+	if b.FilterDefault != nil {
+		result.FilterDefault = b.FilterDefault
+	}
+
 	if b.DisableDispatchedJobSummaryMetrics {
 		result.DisableDispatchedJobSummaryMetrics = b.DisableDispatchedJobSummaryMetrics
 	}

command/agent/config_parse.go

@@ -735,6 +735,7 @@ func parseTelemetry(result **Telemetry, list *ast.ObjectList) error {
 		"disable_tagged_metrics",
 		"backwards_compatible_metrics",
 		"prefix_filter",
+		"filter_default",
 		"disable_dispatched_job_summary_metrics",
 	}
 	if err := helper.CheckHCLKeys(listVal, valid); err != nil {

website/source/docs/configuration/telemetry.html.md

@@ -64,12 +64,16 @@ The following options are available on all telemetry configurations.
   only be added to tagged metrics. Note that this option is used to transition
   monitoring to tagged metrics and will eventually be deprecated.
 
-
 - `disable_tagged_metrics` `(bool: false)` - Specifies if Nomad should not emit
   tagged metrics and only emit metrics compatible with versions below Nomad
   0.7. Note that this option is used to transition monitoring to tagged
   metrics and will eventually be deprecated.
 
+- `filter_default` `(bool: true)` - This controls whether to allow metrics that
+  have not been specified by the filter. Defaults to true, which will allow all
+  metrics when no filters are provided. When set to false with no filters, no
+  metrics will be sent.
+
 - `prefix_filter` `(list: [])` - This is a list of filter rules to apply for
   allowing/blocking metrics by prefix. A leading "<b>+</b>" will enable any
   metrics with the given prefix, and a leading "<b>-</b>" will block them. If