Add doc strings to help explain why changes are the way they are

libbeat/cmd/instance/beat.go

@@ -1486,6 +1486,11 @@ func sanitizeIPs(ips []string) []string {
 	return validIPs
 }
 
+// promoteOutputQueueSettings checks to see if the output
+// configuration has queue settings defined and if so it promotes them
+// to the top level queue settings.  This is done to allow existing
+// behavior of specifying queue settings at the top level or like
+// elastic-agent that specifies queue settings under the output
 func promoteOutputQueueSettings(bc *beatConfig) error {
 	if bc.Output.IsSet() && bc.Output.Config().Enabled() {
 		pc := pipeline.Config{}

libbeat/outputs/util.go

@@ -31,8 +31,10 @@ import (
 // loading an output must return an error.
 func Fail(err error) (Group, error) { return Group{}, err }
 
-// Success create a valid output Group response for a set of client instances.
-// The first argument is expected to contain a queue config.Namespace.
+// Success create a valid output Group response for a set of client
+// instances.  The first argument is expected to contain a queue
+// config.Namespace.  The queue config is passed to assign the queue
+// factory when elastic-agent reloads the output.
 func Success(cfg config.Namespace, batchSize, retry int, clients ...Client) (Group, error) {
 	var q queue.QueueFactory
 	if cfg.IsSet() && cfg.Config().Enabled() {
@@ -75,6 +77,8 @@ func NetworkClients(netclients []NetworkClient) []Client {
 
 // SuccessNet create a valid output Group and creates client instances
 // The first argument is expected to contain a queue config.Namespace.
+// The queue config is passed to assign the queue factory when
+// elastic-agent reloads the output.
 func SuccessNet(cfg config.Namespace, loadbalance bool, batchSize, retry int, netclients []NetworkClient) (Group, error) {
 
 	if !loadbalance {

libbeat/publisher/pipeline/controller.go

@@ -60,8 +60,14 @@ type outputController struct {
 
 	workerChan chan publisher.Batch
 
-	consumer       *eventConsumer
-	workers        []outputWorker
+	consumer *eventConsumer
+	workers  []outputWorker
+	// The InputQueueSize can be set when the Beat is started, in
+	// libbeat/cmd/instance/Settings we need to preserve that
+	// value and pass it into the queue factory.  The queue
+	// factory could be made from elastic-agent output
+	// configuration reloading which doesn't have access to this
+	// setting.
 	inputQueueSize int
 }