[exporter/loadbalancing] Fix memory leaks (open-telemetry#31050)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
This fixes a few goroutine leaks in the loadbalancing exporter.

1. `metrics`, `traces`, and `logs` exporters were starting their
respective load balancers, but were not shutting them down. This adds
each respective shutdown call.
2. The `loadbalancer` was starting the resolver but never shutting it
down. This adds a shutdown call to the resolver.
3. The static resolver was starting resolvers for each passed in
exporter, but never shut them down. This adds a shutdown call for each
resolver in the static resolver.

Also added a couple missing `Shutdown` calls from tests.

**Link to tracking Issue:** <Issue number if applicable>
open-telemetry#30438

**Testing:** <Describe what testing was performed and which tests were
added.>
All existing tests are passing as well as added goleak checks.

.chloggen/goleak_loadbalancingexp.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: loadbalancingexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix memory leaks on shutdown
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [31050]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

exporter/loadbalancingexporter/go.mod

@@ -16,6 +16,7 @@ require (
 	go.opentelemetry.io/collector/semconv v0.96.1-0.20240306115632-b2693620eff6
 	go.opentelemetry.io/otel/metric v1.24.0
 	go.opentelemetry.io/otel/trace v1.24.0
+	go.uber.org/goleak v1.3.0
 	go.uber.org/multierr v1.11.0
 	go.uber.org/zap v1.27.0
 	k8s.io/api v0.29.2

exporter/loadbalancingexporter/loadbalancer.go

@@ -168,9 +168,10 @@ func endpointFound(endpoint string, endpoints []string) bool {
 	return false
 }
 
-func (lb *loadBalancer) Shutdown(context.Context) error {
+func (lb *loadBalancer) Shutdown(ctx context.Context) error {
+	err := lb.res.shutdown(ctx)
 	lb.stopped = true
-	return nil
+	return err
 }
 
 // exporterAndEndpoint returns the exporter and the endpoint for the given identifier.

exporter/loadbalancingexporter/loadbalancer_test.go

@@ -134,6 +134,7 @@ func TestWithDNSResolverNoEndpoints(t *testing.T) {
 
 	err = p.Start(context.Background(), componenttest.NewNopHost())
 	require.NoError(t, err)
+	defer func() { assert.NoError(t, p.Shutdown(context.Background())) }()
 
 	// test
 	_, e, _ := p.exporterAndEndpoint([]byte{128, 128, 0, 0})

exporter/loadbalancingexporter/log_exporter.go

@@ -57,13 +57,14 @@ func (e *logExporterImp) Start(ctx context.Context, host component.Host) error {
 	return e.loadBalancer.Start(ctx, host)
 }
 
-func (e *logExporterImp) Shutdown(context.Context) error {
+func (e *logExporterImp) Shutdown(ctx context.Context) error {
 	if !e.started {
 		return nil
 	}
+	err := e.loadBalancer.Shutdown(ctx)
 	e.started = false
 	e.shutdownWg.Wait()
-	return nil
+	return err
 }
 
 func (e *logExporterImp) ConsumeLogs(ctx context.Context, ld plog.Logs) error {

exporter/loadbalancingexporter/metrics_exporter.go

@@ -74,10 +74,11 @@ func (e *metricExporterImp) Start(ctx context.Context, host component.Host) erro
 	return e.loadBalancer.Start(ctx, host)
 }
 
-func (e *metricExporterImp) Shutdown(context.Context) error {
+func (e *metricExporterImp) Shutdown(ctx context.Context) error {
+	err := e.loadBalancer.Shutdown(ctx)
 	e.stopped = true
 	e.shutdownWg.Wait()
-	return nil
+	return err
 }
 
 func (e *metricExporterImp) ConsumeMetrics(ctx context.Context, md pmetric.Metrics) error {

exporter/loadbalancingexporter/package_test.go

@@ -0,0 +1,17 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package loadbalancingexporter
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+// The IgnoreTopFunction call prevents catching the leak generated by opencensus
+// defaultWorker.Start which at this time is part of the package's init call.
+// See https://github.com/census-instrumentation/opencensus-go/issues/1191 for more information.
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m, goleak.IgnoreTopFunction("go.opencensus.io/stats/view.(*worker).start"))
+}

exporter/loadbalancingexporter/resolver_dns_test.go

@@ -107,6 +107,7 @@ func TestCantResolve(t *testing.T) {
 
 	// verify
 	assert.NoError(t, err)
+	assert.NoError(t, res.shutdown(context.Background()))
 }
 
 func TestOnChange(t *testing.T) {

exporter/loadbalancingexporter/resolver_static.go

@@ -49,7 +49,13 @@ func (r *staticResolver) start(ctx context.Context) error {
 	return err
 }
 
-func (r *staticResolver) shutdown(_ context.Context) error {
+func (r *staticResolver) shutdown(context.Context) error {
+	r.endpoints = nil
+
+	for _, callback := range r.onChangeCallbacks {
+		callback(r.endpoints)
+	}
+
 	return nil
 }
 

exporter/loadbalancingexporter/trace_exporter.go

@@ -72,10 +72,11 @@ func (e *traceExporterImp) Start(ctx context.Context, host component.Host) error
 	return e.loadBalancer.Start(ctx, host)
 }
 
-func (e *traceExporterImp) Shutdown(context.Context) error {
+func (e *traceExporterImp) Shutdown(ctx context.Context) error {
+	err := e.loadBalancer.Shutdown(ctx)
 	e.stopped = true
 	e.shutdownWg.Wait()
-	return nil
+	return err
 }
 
 func (e *traceExporterImp) ConsumeTraces(ctx context.Context, td ptrace.Traces) error {