[Heartbeat] Limit browser jobs to 2 by default (#32564) (#32566)

Fixes #32082 by limiting browser jobs to 2. Users can still override this with the global heartbeat.jobs.browser.limit: 42.

This also fixes a previously unknown bug, where changing the heartbeat.jobs.*.limit values would cause heartbeat to crash with a panic. This appears to be a bug ingo-ucfg. The workaround this PR adds is moving from map[string]JobLimit to map[string]*JobLimit, which doesn't trigger the same reflection issues.

(cherry picked from commit cdd37ca)

Co-authored-by: Andrew Cholakian <[email protected]>

CHANGELOG.next.asciidoc

@@ -21,6 +21,7 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 *Heartbeat*
 - Browser monitors (beta) no write to the `synthetics-*` index prefix. {pull}32064[32064]
 - Setting a custom index for a given monitor is now deprecated. Streams are preferred. {pull}32064[32064]
+- Browserc monitors now default to a max concurrency of two. {pull}32564[32564]
 
 
 *Metricbeat*

heartbeat/config/config.go

@@ -32,7 +32,7 @@ type Config struct {
 	ConfigMonitors *conf.C              `config:"config.monitors"`
 	Scheduler      Scheduler            `config:"scheduler"`
 	Autodiscover   *autodiscover.Config `config:"autodiscover"`
-	Jobs           map[string]JobLimit  `config:"jobs"`
+	Jobs           map[string]*JobLimit `config:"jobs"`
 }
 
 type JobLimit struct {
@@ -46,4 +46,10 @@ type Scheduler struct {
 }
 
 // DefaultConfig is the canonical instantiation of Config.
-var DefaultConfig = Config{}
+var DefaultConfig = Config{
+	Jobs: map[string]*JobLimit{
+		"browser": {
+			Limit: 2,
+		},
+	},
+}

heartbeat/scheduler/schedjob_test.go

@@ -99,7 +99,7 @@ func TestSchedJobRun(t *testing.T) {
 
 // testRecursiveForkingJob tests that a schedJob that splits into multiple parallel pieces executes without error
 func TestRecursiveForkingJob(t *testing.T) {
-	s := Create(1000, monitoring.NewRegistry(), tarawaTime(), map[string]config.JobLimit{
+	s := Create(1000, monitoring.NewRegistry(), tarawaTime(), map[string]*config.JobLimit{
 		"atype": {Limit: 1},
 	}, false)
 	ran := batomic.NewInt(0)

heartbeat/scheduler/scheduler.go

@@ -72,18 +72,19 @@ type Schedule interface {
 	RunOnInit() bool
 }
 
-func getJobLimitSem(jobLimitByType map[string]config.JobLimit) map[string]*semaphore.Weighted {
+func getJobLimitSem(jobLimitByType map[string]*config.JobLimit) map[string]*semaphore.Weighted {
 	jobLimitSem := map[string]*semaphore.Weighted{}
 	for jobType, jobLimit := range jobLimitByType {
 		if jobLimit.Limit > 0 {
+			logp.L().Infof("limiting to %d concurrent jobs for '%s' type", jobLimit.Limit, jobType)
 			jobLimitSem[jobType] = semaphore.NewWeighted(jobLimit.Limit)
 		}
 	}
 	return jobLimitSem
 }
 
 // NewWithLocation creates a new Scheduler using the given runAt zone.
-func Create(limit int64, registry *monitoring.Registry, location *time.Location, jobLimitByType map[string]config.JobLimit, runOnce bool) *Scheduler {
+func Create(limit int64, registry *monitoring.Registry, location *time.Location, jobLimitByType map[string]*config.JobLimit, runOnce bool) *Scheduler {
 	ctx, cancelCtx := context.WithCancel(context.Background())
 
 	if limit < 1 {

heartbeat/scheduler/scheduler_test.go

@@ -245,10 +245,10 @@ func TestSchedTaskLimits(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			var jobConfigByType = map[string]config.JobLimit{}
+			var jobConfigByType = map[string]*config.JobLimit{}
 			jobType := "http"
 			if tt.limit > 0 {
-				jobConfigByType = map[string]config.JobLimit{
+				jobConfigByType = map[string]*config.JobLimit{
 					jobType: {Limit: tt.limit},
 				}
 			}