feat: require passing registries for metrics setup (#247)

## What does this PR do?

remove global registry usage and require explicitly passing system and
process registry
also fix compile errors for other oses

## Why is it important?

move away from global registries similar to what has been recently done
in beats

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## Related issues

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- Closes #123
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-

Author: kruskall

report/metrics_common.go

@@ -27,14 +27,12 @@ import (
 )
 
 var (
-	ephemeralID    uuid.UUID
-	processMetrics *monitoring.Registry
-	startTime      time.Time
+	ephemeralID uuid.UUID
+	startTime   time.Time
 )
 
 func init() {
 	startTime = time.Now()
-	processMetrics = monitoring.Default.NewRegistry("beat")
 
 	var err error
 	ephemeralID, err = uuid.NewV4()

report/metrics_report_test.go

@@ -30,7 +30,9 @@ import (
 )
 
 func TestSystemMetricsReport(t *testing.T) {
-	err := SetupMetrics(logptest.NewTestingLogger(t, ""), "TestSys", "test")
+	systemMetrics := monitoring.NewRegistry()
+	processMetrics := monitoring.NewRegistry()
+	err := SetupMetrics(logptest.NewTestingLogger(t, ""), "TestSys", "test", systemMetrics, processMetrics)
 	require.NoError(t, err)
 
 	var gotCPU, gotMem, gotInfo atomic.Bool

report/setup.go

@@ -31,49 +31,17 @@ import (
 )
 
 var (
-	systemMetrics *monitoring.Registry
-
 	processStats *process.Stats
 )
 
-func init() {
-	systemMetrics = monitoring.Default.NewRegistry("system")
-}
-
-type option struct {
-	systemMetrics  *monitoring.Registry
-	processMetrics *monitoring.Registry
-}
-
-type OptionFunc func(o *option)
-
-func WithProcessRegistry(r *monitoring.Registry) OptionFunc {
-	return func(o *option) {
-		o.processMetrics = r
-	}
-}
-
-func WithSystemRegistry(r *monitoring.Registry) OptionFunc {
-	return func(o *option) {
-		o.systemMetrics = r
-	}
-}
-
 // monitoringCgroupsHierarchyOverride is an undocumented environment variable which
 // overrides the cgroups path under /sys/fs/cgroup, which should be set to "/" when running
 // Elastic Agent under Docker.
 const monitoringCgroupsHierarchyOverride = "LIBBEAT_MONITORING_CGROUPS_HIERARCHY_OVERRIDE"
 
 // SetupMetrics creates a basic suite of metrics handlers for monitoring, including build info and system resources
-func SetupMetrics(logger *logp.Logger, name, version string, opts ...OptionFunc) error {
-	opt := &option{
-		systemMetrics:  systemMetrics,
-		processMetrics: processMetrics,
-	}
-	for _, o := range opts {
-		o(opt)
-	}
-	monitoring.NewFunc(opt.systemMetrics, "cpu", ReportSystemCPUUsage, monitoring.Report)
+func SetupMetrics(logger *logp.Logger, name, version string, systemMetrics *monitoring.Registry, processMetrics *monitoring.Registry) error {
+	monitoring.NewFunc(systemMetrics, "cpu", ReportSystemCPUUsage, monitoring.Report)
 
 	name = processName(name)
 	processStats = &process.Stats{
@@ -89,12 +57,12 @@ func SetupMetrics(logger *logp.Logger, name, version string, opts ...OptionFunc)
 		return fmt.Errorf("failed to init process stats for agent: %w", err)
 	}
 
-	monitoring.NewFunc(opt.processMetrics, "memstats", MemStatsReporter(logger, processStats), monitoring.Report)
-	monitoring.NewFunc(opt.processMetrics, "cpu", InstanceCPUReporter(logger, processStats), monitoring.Report)
-	monitoring.NewFunc(opt.processMetrics, "runtime", ReportRuntime, monitoring.Report)
-	monitoring.NewFunc(opt.processMetrics, "info", infoReporter(name, version), monitoring.Report)
+	monitoring.NewFunc(processMetrics, "memstats", MemStatsReporter(logger, processStats), monitoring.Report)
+	monitoring.NewFunc(processMetrics, "cpu", InstanceCPUReporter(logger, processStats), monitoring.Report)
+	monitoring.NewFunc(processMetrics, "runtime", ReportRuntime, monitoring.Report)
+	monitoring.NewFunc(processMetrics, "info", infoReporter(name, version), monitoring.Report)
 
-	setupPlatformSpecificMetrics(logger, processStats, opt.systemMetrics, opt.processMetrics)
+	setupPlatformSpecificMetrics(logger, processStats, systemMetrics, processMetrics)
 
 	return nil
 }

report/setup_other.go

@@ -23,9 +23,12 @@
 
 package report
 
-import "github.com/elastic/elastic-agent-libs/logp"
+import (
+	"github.com/elastic/elastic-agent-libs/logp"
+	"github.com/elastic/elastic-agent-libs/monitoring"
+)
 
-func SetupMetrics(logger *logp.Logger, name, version string) error {
+func SetupMetrics(logger *logp.Logger, name, version string, systemMetrics *monitoring.Registry, processMetrics *monitoring.Registry) error {
 	logp.Warn("Metrics not implemented for this OS.")
 	return nil
 }