feat: Add lazy mode argument to pyroscope.ebpf (#4824)

Author: luweglarz

CHANGELOG.md

@@ -90,6 +90,8 @@ v1.12.0
 
 - Add a `regex` argument to the `structured_metadata` stage in `loki.process` to extract labels matching a regular expression. (@timonegk)
 
+- Add `lazy_mode` argument to the `pyroscope.ebpf` to defer eBPF profiler startup until there are targets to profile. (@luweglarz)
+
 - OpenTelemetry Collector dependencies upgraded from v0.134.0 to v0.139.0. (@dehaansa)
   - All `otelcol.receiver.*` components leveraging an HTTP server can configure HTTP keep alive behavior with `keep_alives_enabled`.
   - All `otelcol.exporter.*` components providing the `sending_queue` > `batch` block have default `batch` values.

docs/sources/reference/components/pyroscope/pyroscope.ebpf.md

@@ -78,6 +78,7 @@ You can use the following arguments with `pyroscope.ebpf`:
 | `v8_enabled`              | `bool`                   | A flag to enable/disable V8 profiling.                                                                               | `true`   | no       |
 | `off_cpu_threshold`       | `float`                  | A flag to adjust the off-cpu profiling threshold between 0 and 1 as float.                                           | `0`      | no       |
 | `verbose_mode`            | `bool`                   | Enable verbose logging for the eBPF profiler.                                                                        | `false`  | no       |
+| `lazy_mode`               | `bool`                   | Enable lazy mode to defer eBPF profiler startup until targets are discovered.                                        | `false`  | no       |
 
 Only the `forward_to` and `targets` fields are required.
 Omitted fields take their default values.

internal/component/pyroscope/ebpf/args.go

@@ -25,6 +25,7 @@ type Arguments struct {
 	LoadProbe           bool                   `alloy:"load_probe,attr,optional"`
 	UProbeLinks         []string               `alloy:"u_probe_links,attr,optional"`
 	VerboseMode         bool                   `alloy:"verbose_mode,attr,optional"`
+	LazyMode            bool                   `alloy:"lazy_mode,attr,optional"`
 	DeprecatedArguments DeprecatedArguments    `alloy:",squash"`
 
 	// undocumented

internal/component/pyroscope/ebpf/ebpf_linux.go

@@ -122,6 +122,14 @@ type Component struct {
 
 func (c *Component) Run(ctx context.Context) error {
 	c.checkTraceFS()
+
+	if c.args.LazyMode && len(c.args.Targets) == 0 {
+		_ = level.Info(c.logger).Log("msg", "lazy mode enabled, waiting for targets to profile")
+		if err := c.waitForTargets(ctx); err != nil {
+			return err
+		}
+	}
+
 	ctlr := controller.New(c.cfg)
 	const sessionMaxErrors = 3
 	var err error
@@ -156,16 +164,34 @@ func (c *Component) Run(ctx context.Context) error {
 			case <-ctx.Done():
 				return nil
 			case newArgs := <-c.argsUpdate:
-				c.args = newArgs
-				c.targetFinder.Update(c.args.targetsOptions(c.dynamicProfilingPolicy))
-				c.appendable.UpdateChildren(newArgs.ForwardTo)
-				c.metrics.targetsActive.Set(float64(len(c.args.Targets)))
+				c.updateArgs(newArgs)
 			}
 		}
 	}, func(error) {})
 	return g.Run()
 }
 
+func (c *Component) updateArgs(newArgs Arguments) {
+	c.args = newArgs
+	c.targetFinder.Update(c.args.targetsOptions(c.dynamicProfilingPolicy))
+	c.appendable.UpdateChildren(newArgs.ForwardTo)
+	c.metrics.targetsActive.Set(float64(len(c.args.Targets)))
+}
+
+func (c *Component) waitForTargets(ctx context.Context) error {
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case newArgs := <-c.argsUpdate:
+			c.updateArgs(newArgs)
+			if len(c.args.Targets) > 0 {
+				return nil
+			}
+		}
+	}
+}
+
 func (c *Component) Update(args component.Arguments) error {
 	newArgs := args.(Arguments)
 	select {
@@ -244,6 +270,7 @@ func NewDefaultArguments() Arguments {
 		LoadProbe:       false,
 		UProbeLinks:     []string{},
 		VerboseMode:     false,
+		LazyMode:        false,
 
 		// undocumented
 		PyroscopeDynamicProfilingPolicy: true,