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Limit the number of SSE Subscribers to 16 by default 

Signed-off-by: Julien <roidelapluie@o11y.eu>
pull/14994/head
Julien 2 months ago
parent
7aa4721373
commit
f9bbad1148
7 changed files with 94 additions and 46 deletions
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  1. 52
      cmd/prometheus/main.go
  2. 1
      docs/command-line/prometheus.md
  3. 25
      web/api/notifications.go
  4. 47
      web/api/notifications_test.go
  5. 10
      web/api/v1/api.go
  6. 3
      web/ui/mantine-ui/src/components/NotificationsProvider.tsx
  7. 2
      web/web.go

52
cmd/prometheus/main.go
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@ -135,24 +135,25 @@ func agentOnlyFlag(app *kingpin.Application, name, help string) *kingpin.FlagCla
type flagConfig struct {
configFile string
agentStoragePath string
serverStoragePath string
notifier notifier.Options
forGracePeriod model.Duration
outageTolerance model.Duration
resendDelay model.Duration
maxConcurrentEvals int64
web web.Options
scrape scrape.Options
tsdb tsdbOptions
agent agentOptions
lookbackDelta model.Duration
webTimeout model.Duration
queryTimeout model.Duration
queryConcurrency int
queryMaxSamples int
RemoteFlushDeadline model.Duration
nameEscapingScheme string
agentStoragePath string
serverStoragePath string
notifier notifier.Options
forGracePeriod model.Duration
outageTolerance model.Duration
resendDelay model.Duration
maxConcurrentEvals int64
web web.Options
scrape scrape.Options
tsdb tsdbOptions
agent agentOptions
lookbackDelta model.Duration
webTimeout model.Duration
queryTimeout model.Duration
queryConcurrency int
queryMaxSamples int
RemoteFlushDeadline model.Duration
nameEscapingScheme string
maxNotificationsSubscribers int
enableAutoReload bool
autoReloadInterval model.Duration
@ -274,17 +275,13 @@ func main() {
)
}
notifs := api.NewNotifications(prometheus.DefaultRegisterer)
cfg := flagConfig{
notifier: notifier.Options{
Registerer: prometheus.DefaultRegisterer,
},
web: web.Options{
Registerer: prometheus.DefaultRegisterer,
Gatherer: prometheus.DefaultGatherer,
NotificationsSub: notifs.Sub,
NotificationsGetter: notifs.Get,
Registerer: prometheus.DefaultRegisterer,
Gatherer: prometheus.DefaultGatherer,
},
promlogConfig: promlog.Config{},
}
@ -319,6 +316,9 @@ func main() {
a.Flag("web.max-connections", "Maximum number of simultaneous connections across all listeners.").
Default("512").IntVar(&cfg.web.MaxConnections)
a.Flag("web.max-notifications-subscribers", "Limits the maximum number of subscribers that can concurrently receive live notifications. If the limit is reached, new subscription requests will be denied until existing connections close.").
Default("16").IntVar(&cfg.maxNotificationsSubscribers)
a.Flag("web.external-url",
"The URL under which Prometheus is externally reachable (for example, if Prometheus is served via a reverse proxy). Used for generating relative and absolute links back to Prometheus itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Prometheus. If omitted, relevant URL components will be derived automatically.").
PlaceHolder("<URL>").StringVar(&cfg.prometheusURL)
@ -500,6 +500,10 @@ func main() {
logger := promlog.New(&cfg.promlogConfig)
notifs := api.NewNotifications(cfg.maxNotificationsSubscribers, prometheus.DefaultRegisterer)
cfg.web.NotificationsSub = notifs.Sub
cfg.web.NotificationsGetter = notifs.Get
if err := cfg.setFeatureListOptions(logger); err != nil {
fmt.Fprintln(os.Stderr, fmt.Errorf("Error parsing feature list: %w", err))
os.Exit(1)

1
docs/command-line/prometheus.md
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@ -21,6 +21,7 @@ The Prometheus monitoring server
| <code class="text-nowrap">--web.config.file</code> | [EXPERIMENTAL] Path to configuration file that can enable TLS or authentication. | |
| <code class="text-nowrap">--web.read-timeout</code> | Maximum duration before timing out read of the request, and closing idle connections. | `5m` |
| <code class="text-nowrap">--web.max-connections</code> | Maximum number of simultaneous connections across all listeners. | `512` |
| <code class="text-nowrap">--web.max-notifications-subscribers</code> | Limits the maximum number of subscribers that can concurrently receive live notifications. If the limit is reached, new subscription requests will be denied until existing connections close. | `16` |
| <code class="text-nowrap">--web.external-url</code> | The URL under which Prometheus is externally reachable (for example, if Prometheus is served via a reverse proxy). Used for generating relative and absolute links back to Prometheus itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Prometheus. If omitted, relevant URL components will be derived automatically. | |
| <code class="text-nowrap">--web.route-prefix</code> | Prefix for the internal routes of web endpoints. Defaults to path of --web.external-url. | |
| <code class="text-nowrap">--web.user-assets</code> | Path to static asset directory, available at /user. | |

25
web/api/notifications.go
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@ -34,9 +34,10 @@ type Notification struct {
// Notifications stores a list of Notification objects.
// It also manages live subscribers that receive notifications via channels.
type Notifications struct {
mu sync.Mutex
notifications []Notification
subscribers map[chan Notification]struct{} // Active subscribers.
mu sync.Mutex
notifications []Notification
subscribers map[chan Notification]struct{} // Active subscribers.
maxSubscribers int
subscriberGauge prometheus.Gauge
notificationsSent prometheus.Counter
@ -44,9 +45,10 @@ type Notifications struct {
}
// NewNotifications creates a new Notifications instance.
func NewNotifications(reg prometheus.Registerer) *Notifications {
func NewNotifications(maxSubscribers int, reg prometheus.Registerer) *Notifications {
n := &Notifications{
subscribers: make(map[chan Notification]struct{}),
subscribers: make(map[chan Notification]struct{}),
maxSubscribers: maxSubscribers,
subscriberGauge: prometheus.NewGauge(prometheus.GaugeOpts{
Namespace: "prometheus",
Subsystem: "api",
@ -147,10 +149,16 @@ func (n *Notifications) Get() []Notification {
// Sub allows a client to subscribe to live notifications.
// It returns a channel where the subscriber will receive notifications and a function to unsubscribe.
// Each subscriber has its own goroutine to handle notifications and prevent blocking.
func (n *Notifications) Sub() (<-chan Notification, func()) {
func (n *Notifications) Sub() (<-chan Notification, func(), bool) {
n.mu.Lock()
defer n.mu.Unlock()
if len(n.subscribers) >= n.maxSubscribers {
return nil, nil, false
}
ch := make(chan Notification, 10) // Buffered channel to prevent blocking.
n.mu.Lock()
// Add the new subscriber to the list.
n.subscribers[ch] = struct{}{}
n.subscriberGauge.Set(float64(len(n.subscribers)))
@ -159,7 +167,6 @@ func (n *Notifications) Sub() (<-chan Notification, func()) {
for _, notification := range n.notifications {
ch <- notification
}
n.mu.Unlock()
// Unsubscribe function to remove the channel from subscribers.
unsubscribe := func() {
@ -172,5 +179,5 @@ func (n *Notifications) Sub() (<-chan Notification, func()) {
n.subscriberGauge.Set(float64(len(n.subscribers)))
}
return ch, unsubscribe
return ch, unsubscribe, true
}

47
web/api/notifications_test.go
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@ -23,7 +23,7 @@ import (
// TestNotificationLifecycle tests adding, modifying, and deleting notifications.
func TestNotificationLifecycle(t *testing.T) {
notifs := NewNotifications(nil)
notifs := NewNotifications(10, nil)
// Add a notification.
notifs.AddNotification("Test Notification 1")
@ -47,10 +47,11 @@ func TestNotificationLifecycle(t *testing.T) {
// TestSubscriberReceivesNotifications tests that a subscriber receives notifications, including modifications and deletions.
func TestSubscriberReceivesNotifications(t *testing.T) {
notifs := NewNotifications(nil)
notifs := NewNotifications(10, nil)
// Subscribe to notifications.
sub, unsubscribe := notifs.Sub()
sub, unsubscribe, ok := notifs.Sub()
require.True(t, ok)
var wg sync.WaitGroup
wg.Add(1)
@ -103,12 +104,14 @@ func TestSubscriberReceivesNotifications(t *testing.T) {
// TestMultipleSubscribers tests that multiple subscribers receive notifications independently.
func TestMultipleSubscribers(t *testing.T) {
notifs := NewNotifications(nil)
notifs := NewNotifications(10, nil)
// Subscribe two subscribers to notifications.
sub1, unsubscribe1 := notifs.Sub()
sub1, unsubscribe1, ok1 := notifs.Sub()
require.True(t, ok1)
sub2, unsubscribe2 := notifs.Sub()
sub2, unsubscribe2, ok2 := notifs.Sub()
require.True(t, ok2)
var wg sync.WaitGroup
wg.Add(2)
@ -157,10 +160,11 @@ func TestMultipleSubscribers(t *testing.T) {
// TestUnsubscribe tests that unsubscribing prevents further notifications from being received.
func TestUnsubscribe(t *testing.T) {
notifs := NewNotifications(nil)
notifs := NewNotifications(10, nil)
// Subscribe to notifications.
sub, unsubscribe := notifs.Sub()
sub, unsubscribe, ok := notifs.Sub()
require.True(t, ok)
var wg sync.WaitGroup
wg.Add(1)
@ -190,3 +194,30 @@ func TestUnsubscribe(t *testing.T) {
require.Len(t, receivedNotifications, 1, "Expected 1 notification before unsubscribe.")
require.Equal(t, "Test Notification 1", receivedNotifications[0].Text, "Unexpected notification text.")
}
// TestMaxSubscribers tests that exceeding the max subscribers limit prevents additional subscriptions.
func TestMaxSubscribers(t *testing.T) {
maxSubscribers := 2
notifs := NewNotifications(maxSubscribers, nil)
// Subscribe the maximum number of subscribers.
_, unsubscribe1, ok1 := notifs.Sub()
require.True(t, ok1, "Expected first subscription to succeed.")
_, unsubscribe2, ok2 := notifs.Sub()
require.True(t, ok2, "Expected second subscription to succeed.")
// Try to subscribe more than the max allowed.
_, _, ok3 := notifs.Sub()
require.False(t, ok3, "Expected third subscription to fail due to max subscriber limit.")
// Unsubscribe one subscriber and try again.
unsubscribe1()
_, unsubscribe4, ok4 := notifs.Sub()
require.True(t, ok4, "Expected subscription to succeed after unsubscribing a subscriber.")
// Clean up the subscriptions.
unsubscribe2()
unsubscribe4()
}

10
web/api/v1/api.go
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@ -215,7 +215,7 @@ type API struct {
isAgent bool
statsRenderer StatsRenderer
notificationsGetter func() []api.Notification
notificationsSub func() (<-chan api.Notification, func())
notificationsSub func() (<-chan api.Notification, func(), bool)
remoteWriteHandler http.Handler
remoteReadHandler http.Handler
@ -250,7 +250,7 @@ func NewAPI(
runtimeInfo func() (RuntimeInfo, error),
buildInfo *PrometheusVersion,
notificationsGetter func() []api.Notification,
notificationsSub func() (<-chan api.Notification, func()),
notificationsSub func() (<-chan api.Notification, func(), bool),
gatherer prometheus.Gatherer,
registerer prometheus.Registerer,
statsRenderer StatsRenderer,
@ -1690,7 +1690,11 @@ func (api *API) notificationsSSE(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Connection", "keep-alive")
// Subscribe to notifications.
notifications, unsubscribe := api.notificationsSub()
notifications, unsubscribe, ok := api.notificationsSub()
if !ok {
w.WriteHeader(http.StatusNoContent)
return
}
defer unsubscribe()
// Set up a flusher to push the response to the client.

3
web/ui/mantine-ui/src/components/NotificationsProvider.tsx
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@ -42,7 +42,8 @@ export const NotificationsProvider: React.FC<{ children: React.ReactNode }> = ({
eventSource.onerror = () => {
eventSource.close();
setIsConnectionError(true);
// We do not call setIsConnectionError(true), we only set it to true if
// the fallback API does not work either.
setShouldFetchFromAPI(true);
};

2
web/web.go
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@ -268,7 +268,7 @@ type Options struct {
Notifier *notifier.Manager
Version *PrometheusVersion
NotificationsGetter func() []api.Notification
NotificationsSub func() (<-chan api.Notification, func())
NotificationsSub func() (<-chan api.Notification, func(), bool)
Flags map[string]string
ListenAddresses []string

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