Repository: TwiN/gatus

Issue:
Repeating notifications
### Describe the feature request

Ability to send repeated notifications every x min/hr if the endpoint is still offline/dead.


### Why do you personally want this feature to be implemented?

We now had over 300 nodes monitoring via Gatus and we received the notifications via Slack and Telegram. One scenario is when some nodes are offline during the weekend. We always forget to fix them in the next workday.

I've tried some other services and seems like it's a common feature to alert repeatedly if something still goes wrong.

### How long have you been using this project?

_No response_

### Additional information

_No response_

Discussion:
@TwiN: Sounds like a good idea!

Something like this:
```yaml
    alerts:
      - type: slack
        enabled: true
        description: "healthcheck failed 3 times in a row"
        send-on-resolved: true
        repeating: true
```

That said, not all alerting providers should allow this.
For instance, `pagerduty` incidents need an acknowledgement on resolve, so we probably don't want to trigger multiple alerts simultaneously for pagerduty. For Slack, Discord, Teams, Telegram, etc. it shouldn't be an issue.@diamonddelt: Bumping this because we'd also be interested in having this feature, particularly for the MS Teams alerting hooks. We already use send-on-resolved, but if a service was down for 6+ days and the small team missed the initial message sent to a noisy MS Teams channel, it's easy to miss or forget unless it periodically reminds you it is still failing.@mxcd: From what I can see, #614 is implementing this functionality ready for review@illia-weisser: I want this!@TwiN: This has been implemented and should be available under the latest tag.

Could anybody give it a try on their end and let me know if it works as intended?@xconverge: I am not sure this is working for me, I am using:

```
alerting:
  slack:
    webhook-url: xyz
    default-alert:
      description: "Health Check"
      send-on-resolved: true
      failure-threshold: 2
      success-threshold: 2
      minimum-reminder-interval: 48h
```

and it has been more than 48h and I did not get a reminder

I will look into it a bit more but wanted to see if anyone has had success with this yet?

@day1118: > I am not sure this is working for me

I tried a 5m reminder and it didn't work for me either.@xconverge: @day1118 thanks for the confirmation, I was able to fix it in https://github.com/TwiN/gatus/pull/1226 an issue merging/applying the default config

Until that is merged/released you can specify it per-endpoint and it should work:

```
endpoints:
  - name: test-alerting
    x: ...
    y: ...
    alerts:
      - type: xyz
        minimum-reminder-interval: 5m
```@TwiN: Merged the fix! Thank you for the quick turnaround 

Solution patch:
diff --git a/README.md b/README.md
index 71af2b0f..9343e101 100644
--- a/README.md
+++ b/README.md
@@ -553,16 +553,17 @@ individual endpoints with configurable descriptions and thresholds.
 
 Alerts are configured at the endpoint level like so:
 
-| Parameter                    | Description                                                                    | Default       |
-|:-----------------------------|:-------------------------------------------------------------------------------|:--------------|
-| `alerts`                     | List of all alerts for a given endpoint.                                       | `[]`          |
-| `alerts[].type`              | Type of alert. <br />See table below for all valid types.                      | Required `""` |
-| `alerts[].enabled`           | Whether to enable the alert.                                                   | `true`        |
-| `alerts[].failure-threshold` | Number of failures in a row needed before triggering the alert.                | `3`           |
-| `alerts[].success-threshold` | Number of successes in a row before an ongoing incident is marked as resolved. | `2`           |
-| `alerts[].send-on-resolved`  | Whether to send a notification once a triggered alert is marked as resolved.   | `false`       |
-| `alerts[].description`       | Description of the alert. Will be included in the alert sent.                  | `""`          |
-| `alerts[].provider-override` | Alerting provider configuration override for the given alert type              | `{}`          |
+| Parameter                            | Description                                                                    | Default       |
+|:-------------------------------------|:-------------------------------------------------------------------------------|:--------------|
+| `alerts`                             | List of all alerts for a given endpoint.                                       | `[]`          |
+| `alerts[].type`                      | Type of alert. <br />See table below for all valid types.                      | Required `""` |
+| `alerts[].enabled`                   | Whether to enable the alert.                                                   | `true`        |
+| `alerts[].failure-threshold`         | Number of failures in a row needed before triggering the alert.                | `3`           |
+| `alerts[].success-threshold`         | Number of successes in a row before an ongoing incident is marked as resolved. | `2`           |
+| `alerts[].minimum-reminder-interval` | Configuration for setting an interval between reminders.                       | `""`          |
+| `alerts[].send-on-resolved`          | Whether to send a notification once a triggered alert is marked as resolved.   | `false`       |
+| `alerts[].description`               | Description of the alert. Will be included in the alert sent.                  | `""`          |
+| `alerts[].provider-override`         | Alerting provider configuration override for the given alert type              | `{}`          |
 
 Here's an example of what an alert configuration might look like at the endpoint level:
 ```yaml
diff --git a/alerting/alert/alert.go b/alerting/alert/alert.go
index 52eb5f5d..ebd34c19 100644
--- a/alerting/alert/alert.go
+++ b/alerting/alert/alert.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/TwiN/logr"
 	"gopkg.in/yaml.v3"
@@ -35,6 +36,9 @@ type Alert struct {
 	// SuccessThreshold defines how many successful executions must happen in a row before an ongoing incident is marked as resolved
 	SuccessThreshold int `yaml:"success-threshold"`
 
+	// MinimumReminderInterval is the interval between reminders
+	MinimumReminderInterval time.Duration `yaml:"minimum-reminder-interval,omitempty"`
+
 	// Description of the alert. Will be included in the alert sent.
 	//
 	// This is a pointer, because it is populated by YAML and we need to know whether it was explicitly set to a value
diff --git a/config/endpoint/endpoint.go b/config/endpoint/endpoint.go
index fd1bc305..5153a45b 100644
--- a/config/endpoint/endpoint.go
+++ b/config/endpoint/endpoint.go
@@ -131,6 +131,9 @@ type Endpoint struct {
 
 	// NumberOfSuccessesInARow is the number of successful evaluations in a row
 	NumberOfSuccessesInARow int `yaml:"-"`
+
+	// LastReminderSent is the time at which the last reminder was sent for this endpoint.
+	LastReminderSent time.Time `yaml:"-"`
 }
 
 // IsEnabled returns whether the endpoint is enabled or not
diff --git a/watchdog/alerting.go b/watchdog/alerting.go
index 866ed667..4e09477d 100644
--- a/watchdog/alerting.go
+++ b/watchdog/alerting.go
@@ -2,7 +2,9 @@ package watchdog
 
 import (
 	"errors"
+	"log"
 	"os"
+	"time"
 
 	"github.com/TwiN/gatus/v5/alerting"
 	"github.com/TwiN/gatus/v5/config/endpoint"
@@ -30,14 +32,24 @@ func handleAlertsToTrigger(ep *endpoint.Endpoint, result *endpoint.Result, alert
 		if !endpointAlert.IsEnabled() || endpointAlert.FailureThreshold > ep.NumberOfFailuresInARow {
 			continue
 		}
-		if endpointAlert.Triggered {
-			logr.Debugf("[watchdog.handleAlertsToTrigger] Alert for endpoint with key=%s with description='%s' has already been TRIGGERED, skipping", ep.Key(), endpointAlert.GetDescription())
+		// Determine if an initial alert should be sent
+		sendInitialAlert := !endpointAlert.Triggered
+		// Determine if a reminder should be sent
+		sendReminder := endpointAlert.Triggered && endpointAlert.MinimumReminderInterval > 0 && time.Since(ep.LastReminderSent) >= endpointAlert.MinimumReminderInterval
+		// If neither initial alert nor reminder needs to be sent, skip to the next alert
+		if !sendInitialAlert && !sendReminder {
+			logr.Debugf("[watchdog.handleAlertsToTrigger] Alert for endpoint=%s with description='%s' is not due for triggering or reminding, skipping", ep.Name, endpointAlert.GetDescription())
 			continue
 		}
 		alertProvider := alertingConfig.GetAlertingProviderByAlertType(endpointAlert.Type)
 		if alertProvider != nil {
 			logr.Infof("[watchdog.handleAlertsToTrigger] Sending %s alert because alert for endpoint with key=%s with description='%s' has been TRIGGERED", endpointAlert.Type, ep.Key(), endpointAlert.GetDescription())
 			var err error
+			alertType := "reminder"
+			if sendInitialAlert {
+				alertType = "initial"
+			}
+			log.Printf("[watchdog.handleAlertsToTrigger] Sending %s %s alert because alert for endpoint=%s with description='%s' has been TRIGGERED", alertType, endpointAlert.Type, ep.Name, endpointAlert.GetDescription())
 			if os.Getenv("MOCK_ALERT_PROVIDER") == "true" {
 				if os.Getenv("MOCK_ALERT_PROVIDER_ERROR") == "true" {
 					err = errors.New("error")
@@ -48,7 +60,11 @@ func handleAlertsToTrigger(ep *endpoint.Endpoint, result *endpoint.Result, alert
 			if err != nil {
 				logr.Errorf("[watchdog.handleAlertsToTrigger] Failed to send an alert for endpoint with key=%s: %s", ep.Key(), err.Error())
 			} else {
-				endpointAlert.Triggered = true
+				// Mark initial alert as triggered and update last reminder time
+				if sendInitialAlert {
+					endpointAlert.Triggered = true
+				}
+				ep.LastReminderSent = time.Now()
 				if err := store.Get().UpsertTriggeredEndpointAlert(ep, endpointAlert); err != nil {
 					logr.Errorf("[watchdog.handleAlertsToTrigger] Failed to persist triggered endpoint alert for endpoint with key=%s: %s", ep.Key(), err.Error())
 				}



Test patch:
diff --git a/alerting/provider/ilert/ilert_test.go b/alerting/provider/ilert/ilert_test.go
index 3f18d60e..f5040e5e 100644
--- a/alerting/provider/ilert/ilert_test.go
+++ b/alerting/provider/ilert/ilert_test.go
@@ -174,21 +174,21 @@ func TestAlertProvider_BuildRequestBody(t *testing.T) {
 			Provider:     AlertProvider{DefaultConfig: Config{IntegrationKey: "some-integration-key"}},
 			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 3, FailureThreshold: 3, ResolveKey: "123", Type: "ilert", SendOnResolved: &sendOnResolved},
 			Resolved:     false,
-			ExpectedBody: `{"alert":{"Type":"ilert","Enabled":null,"FailureThreshold":3,"SuccessThreshold":3,"Description":"description-1","SendOnResolved":true,"ProviderOverride":null,"ResolveKey":"123","Triggered":false},"name":"endpoint-name","group":"","status":"firing","title":"endpoint-name","details":"description-1","condition_results":[{"condition":"[CONNECTED] == true","success":false},{"condition":"[STATUS] == 200","success":false}],"url":""}`,
+			ExpectedBody: `{"alert":{"Type":"ilert","Enabled":null,"FailureThreshold":3,"SuccessThreshold":3,"MinimumReminderInterval":0,"Description":"description-1","SendOnResolved":true,"ProviderOverride":null,"ResolveKey":"123","Triggered":false},"name":"endpoint-name","group":"","status":"firing","title":"endpoint-name","details":"description-1","condition_results":[{"condition":"[CONNECTED] == true","success":false},{"condition":"[STATUS] == 200","success":false}],"url":""}`,
 		},
 		{
 			Name:         "resolved",
 			Provider:     AlertProvider{DefaultConfig: Config{IntegrationKey: "some-integration-key"}},
 			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 4, FailureThreshold: 3, ResolveKey: "123", Type: "ilert", SendOnResolved: &sendOnResolved},
 			Resolved:     true,
-			ExpectedBody: `{"alert":{"Type":"ilert","Enabled":null,"FailureThreshold":3,"SuccessThreshold":4,"Description":"description-1","SendOnResolved":true,"ProviderOverride":null,"ResolveKey":"123","Triggered":false},"name":"endpoint-name","group":"","status":"resolved","title":"endpoint-name","details":"description-1","condition_results":[{"condition":"[CONNECTED] == true","success":true},{"condition":"[STATUS] == 200","success":true}],"url":""}`,
+			ExpectedBody: `{"alert":{"Type":"ilert","Enabled":null,"FailureThreshold":3,"SuccessThreshold":4,"MinimumReminderInterval":0,"Description":"description-1","SendOnResolved":true,"ProviderOverride":null,"ResolveKey":"123","Triggered":false},"name":"endpoint-name","group":"","status":"resolved","title":"endpoint-name","details":"description-1","condition_results":[{"condition":"[CONNECTED] == true","success":true},{"condition":"[STATUS] == 200","success":true}],"url":""}`,
 		},
 		{
 			Name:         "group-override",
 			Provider:     AlertProvider{DefaultConfig: Config{IntegrationKey: "some-integration-key"}, Overrides: []Override{{Group: "g", Config: Config{IntegrationKey: "different-integration-key"}}}},
 			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3, ResolveKey: "123", Type: "ilert", SendOnResolved: &sendOnResolved},
 			Resolved:     false,
-			ExpectedBody: `{"alert":{"Type":"ilert","Enabled":null,"FailureThreshold":3,"SuccessThreshold":5,"Description":"description-2","SendOnResolved":true,"ProviderOverride":null,"ResolveKey":"123","Triggered":false},"name":"endpoint-name","group":"","status":"firing","title":"endpoint-name","details":"description-2","condition_results":[{"condition":"[CONNECTED] == true","success":false},{"condition":"[STATUS] == 200","success":false}],"url":""}`,
+			ExpectedBody: `{"alert":{"Type":"ilert","Enabled":null,"FailureThreshold":3,"SuccessThreshold":5,"MinimumReminderInterval":0,"Description":"description-2","SendOnResolved":true,"ProviderOverride":null,"ResolveKey":"123","Triggered":false},"name":"endpoint-name","group":"","status":"firing","title":"endpoint-name","details":"description-2","condition_results":[{"condition":"[CONNECTED] == true","success":false},{"condition":"[STATUS] == 200","success":false}],"url":""}`,
 		},
 	}
 
diff --git a/watchdog/alerting_test.go b/watchdog/alerting_test.go
index 2dffd909..21bd7434 100644
--- a/watchdog/alerting_test.go
+++ b/watchdog/alerting_test.go
@@ -3,6 +3,7 @@ package watchdog
 import (
 	"os"
 	"testing"
+	"time"
 
 	"github.com/TwiN/gatus/v5/alerting"
 	"github.com/TwiN/gatus/v5/alerting/alert"
@@ -517,6 +518,48 @@ func TestHandleAlertingWithProviderThatOnlyReturnsErrorOnResolve(t *testing.T) {
 	verify(t, ep, 0, 2, false, "")
 }
 
+func TestHandleAlertingWithMinimumReminderInterval(t *testing.T) {
+	_ = os.Setenv("MOCK_ALERT_PROVIDER", "true")
+	defer os.Clearenv()
+
+	cfg := &config.Config{
+		Alerting: &alerting.Config{
+			Custom: &custom.AlertProvider{
+				DefaultConfig: custom.Config{
+					URL:    "https://twin.sh/health",
+					Method: "GET",
+				},
+			},
+		},
+	}
+	enabled := true
+	ep := &endpoint.Endpoint{
+		URL: "https://example.com",
+		Alerts: []*alert.Alert{
+			{
+				Type:                    alert.TypeCustom,
+				Enabled:                 &enabled,
+				FailureThreshold:        2,
+				SuccessThreshold:        3,
+				SendOnResolved:          &enabled,
+				Triggered:               false,
+				MinimumReminderInterval: 1 * time.Second,
+			},
+		},
+	}
+
+	verify(t, ep, 0, 0, false, "The alert shouldn't start triggered")
+	HandleAlerting(ep, &endpoint.Result{Success: false}, cfg.Alerting)
+	verify(t, ep, 1, 0, false, "The alert shouldn't have triggered")
+	HandleAlerting(ep, &endpoint.Result{Success: false}, cfg.Alerting)
+	verify(t, ep, 2, 0, true, "The alert should've triggered")
+	HandleAlerting(ep, &endpoint.Result{Success: false}, cfg.Alerting)
+	verify(t, ep, 3, 0, true, "The alert should still be triggered")
+	HandleAlerting(ep, &endpoint.Result{Success: false}, cfg.Alerting)
+	verify(t, ep, 4, 0, true, "The alert should still be triggered")
+	HandleAlerting(ep, &endpoint.Result{Success: true}, cfg.Alerting)
+}
+
 func verify(t *testing.T, ep *endpoint.Endpoint, expectedNumberOfFailuresInARow, expectedNumberOfSuccessInARow int, expectedTriggered bool, expectedTriggeredReason string) {
 	if ep.NumberOfFailuresInARow != expectedNumberOfFailuresInARow {
 		t.Errorf("endpoint.NumberOfFailuresInARow should've been %d, got %d", expectedNumberOfFailuresInARow, ep.NumberOfFailuresInARow)