Feat: random jitter in ScheduleNextCheck

internal/config/options.go

@@ -504,6 +504,14 @@ func NewConfigOptions() *configOptions {
 					return validateChoices(rawValue, []string{"round_robin", "entry_frequency"})
 				},
 			},
+			"POLLING_JITTER": {
+				ParsedDuration: 10 * time.Minute,
+				RawValue:       "10",
+				ValueType:      minuteType,
+				Validator: func(rawValue string) error {
+					return validateGreaterOrEqualThan(rawValue, 1)
+				},
+			},
 			"PORT": {
 				ParsedStringValue: "",
 				RawValue:          "",
@@ -902,6 +910,10 @@ func (c *configOptions) PollingScheduler() string {
 	return c.options["POLLING_SCHEDULER"].ParsedStringValue
 }
 
+func (c *configOptions) PollingJitter() time.Duration {
+	return c.options["POLLING_JITTER"].ParsedDuration
+}
+
 func (c *configOptions) Port() string {
 	return c.options["PORT"].ParsedStringValue
 }

internal/model/feed.go

@@ -6,11 +6,13 @@ package model // import "miniflux.app/v2/internal/model"
 import (
 	"fmt"
 	"io"
+	"math/rand"
 	"time"
 
 	"miniflux.app/v2/internal/config"
 )
 
+
 // List of supported schedulers.
 const (
 	SchedulerRoundRobin     = "round_robin"
@@ -117,6 +119,18 @@ func (f *Feed) CheckedNow() {
 	}
 }
 
+// getMaxInterval returns the maximum allowed interval based on the configured polling scheduler.
+func getMaxInterval() time.Duration {
+	switch config.Opts.PollingScheduler() {
+	case SchedulerRoundRobin:
+		return config.Opts.SchedulerRoundRobinMaxInterval()
+	case SchedulerEntryFrequency:
+		return config.Opts.SchedulerEntryFrequencyMaxInterval()
+	default:
+		return config.Opts.SchedulerRoundRobinMaxInterval()
+	}
+}
+
 // ScheduleNextCheck set "next_check_at" of a feed based on the scheduler selected from the configuration.
 func (f *Feed) ScheduleNextCheck(weeklyCount int, refreshDelay time.Duration) time.Duration {
 	// Default to the global config Polling Frequency.
@@ -135,13 +149,16 @@ func (f *Feed) ScheduleNextCheck(weeklyCount int, refreshDelay time.Duration) ti
 	// Use the RSS TTL field, Retry-After, Cache-Control or Expires HTTP headers if defined.
 	interval = max(interval, refreshDelay)
 
-	// Limit the max interval value for misconfigured feeds.
-	switch config.Opts.PollingScheduler() {
-	case SchedulerRoundRobin:
-		interval = min(interval, config.Opts.SchedulerRoundRobinMaxInterval())
-	case SchedulerEntryFrequency:
-		interval = min(interval, config.Opts.SchedulerEntryFrequencyMaxInterval())
-	}
+	// Apply a small random jitter to spread next checks and reduce thundering herds.
+	jitterMax := config.Opts.PollingJitter()
+
+	// No explicit global seeding for math/rand is required since Go 1.20.
+	randomJitter := time.Duration(rand.Int63n(int64(jitterMax + 1)))
+	interval += randomJitter
+
+	// Apply max clamping after randomJitter to avoid exceeding configured caps.
+    maxInterval := getMaxInterval()
+    interval = min(interval, maxInterval)
 
 	f.NextCheckAt = time.Now().Add(interval)
 	return interval

internal/model/feed_test.go

@@ -68,12 +68,15 @@ func TestFeedCheckedNow(t *testing.T) {
 }
 
 func checkTargetInterval(t *testing.T, feed *Feed, targetInterval time.Duration, timeBefore time.Time, message string) {
-	if feed.NextCheckAt.Before(timeBefore.Add(targetInterval)) {
-		t.Errorf(`The next_check_at should be after timeBefore + %s`, message)
-	}
-	if feed.NextCheckAt.After(time.Now().Add(targetInterval)) {
-		t.Errorf(`The next_check_at should be before now + %s`, message)
-	}
+    // Allow a positive jitter up to 10 minutes added by the scheduler.
+    jitterMax := 10 * time.Minute
+
+    if feed.NextCheckAt.Before(timeBefore.Add(targetInterval)) {
+        t.Errorf(`The next_check_at should be after timeBefore + %s`, message)
+    }
+    if feed.NextCheckAt.After(time.Now().Add(targetInterval + jitterMax)) {
+        t.Errorf(`The next_check_at should be before now + %s (with jitter)`, message)
+    }
 }
 
 func TestFeedScheduleNextCheckRoundRobinDefault(t *testing.T) {