Firebase provides alerting for a wide range of project and app management
events. Here are a few example events for when Firebase can send you this
type of alert:

- For Crashlytics, we can alert you if your app has a dramatic increase in crashes.
- For Performance Monitoring, we can alert you if your app's start-up time crosses your configured threshold.
- For App Distribution, we can alert you if one of your testers registers a new iOS device.

Depending on the alert and the [preferences set by the project
member](https://support.google.com/firebase/answer/7276542),
Firebase shows these types of alerts in the Firebase console or sends them
via email.

This page describes how to write functions in Cloud Functions for Firebase (2nd gen)
that handle alert events.

## How does it work?

You can trigger functions in response to alert events emitted by these sources:

- [Handle an App Distribution alert event](https://firebase.google.com/docs/functions/alert-events.md.txt#handle-app-distribution-alerts)
- [Handle a Crashlytics alert event](https://firebase.google.com/docs/functions/alert-events.md.txt#handle-crashlytics-alerts)
- [Handle a Performance Monitoring alert event](https://firebase.google.com/docs/functions/alert-events.md.txt#handle-performance-alerts)

In a typical lifecycle, a function triggered by an alert event does the
following:

1. Listens/waits for a specific alert type to be emitted from Firebase.
2. Triggers when the alert is emitted, and receives the event payload which contains specific information about the event.
3. Invokes your function's code to handle the event payload.

## Trigger a function on alert events

Use the `firebase-functions/v2/alerts` subpackage to write a function that
handles alerts events. The following product-specific examples demonstrate a
workflow where a function uses a webhook to post a message to a Discord channel
when an alert for that product is emitted from Firebase.

> [!IMPORTANT]
> **Important:** Each of these examples assumes that you've already [set up Cloud Functions for Firebase](https://firebase.google.com/docs/functions/get-started.md.txt).

### Handle a Crashlytics alert event

For the following Crashlytics example, you use Cloud Functions for Firebase to
handle an alert event of a new fatal crash issue. This function posts the alert
information in a message to a Discord channel.

![Example crash notification in Discord](https://firebase.google.com/static/docs/functions/images/discord-functions.png)
Example notification for a new fatal crash issue

<br />

The function listens for the event corresponding to Firebase
publishing a new fatal issue:

### Node.js

```javascript
exports.postfatalissuetodiscord = onNewFatalIssuePublished(async (event) => {
```

### Python

```python
@crashlytics_fn.on_new_fatal_issue_published(secrets=["DISCORD_WEBHOOK_URL"])
def post_fatal_issue_to_discord(event: crashlytics_fn.CrashlyticsNewFatalIssueEvent) -> None:
    """Publishes a message to Discord whenever a new Crashlytics fatal issue occurs."""
```

The function then parses the returned event object,
parsing useful information from the event payload and constructing a message to
post to the Discord channel:

### Node.js

```javascript
  // construct a helpful message to send to Discord
  const appId = event.appId;
  const {id, title, subtitle, appVersion} = event.data.payload.issue;
  const message = `
🚨 New fatal issue for ${appId} in version ${appVersion} 🚨

**${title}**

${subtitle}

id: \`${id}\`
`;
```

### Python

```python
    # Construct a helpful message to send to Discord.
    app_id = event.app_id
    issue = event.data.payload.issue
    message = f"""
🚨 New fatal issue for {app_id} in version {issue.app_version} 🚨

# {issue.title}

{issue.subtitle}

ID: `{issue.id}`
""".strip()
```

Finally, the function sends the constructed message to Discord through
an HTTP request:

### Node.js

```javascript
const response = await postMessageToDiscord("Crashlytics Bot", message);
if (response.ok) {
  logger.info(
      `Posted fatal Crashlytics alert ${id} for ${appId} to Discord`,
      event.data.payload,
  );
} else {
  throw new Error(`Discord returned status code ${response.status}`);
}
```

### Python

```python
response = post_message_to_discord("Crashlytics Bot", message, DISCORD_WEBHOOK_URL.value)
if response.ok:
    print(f"Posted fatal Crashlytics alert {issue.id} for {app_id} to Discord.")
    pprint.pp(event.data.payload)
else:
    response.raise_for_status()
```

To learn about all the Crashlytics alert events that you can capture, go to
the reference documentation for
[Crashlytics alerts](https://firebase.google.com/docs/reference/functions/2nd-gen/node/firebase-functions.alerts.crashlytics.md.txt).

### Handle a Performance Monitoring alert event

This example exports a function that listens for performance threshold alert events:

### Node.js

```javascript
exports.postperformancealerttodiscord = onThresholdAlertPublished(
    async (event) => {
```

### Python

```python
@performance_fn.on_threshold_alert_published(secrets=["DISCORD_WEBHOOK_URL"])
def post_performance_alert_to_discord(event: performance_fn.PerformanceThresholdAlertEvent) -> None:
    """Publishes a message to Discord whenever a performance threshold alert is fired."""
```

The function then parses the returned event object, parsing useful information
from the event payload and constructing a message to post to the Discord
channel:

### Node.js

```javascript
      // construct a helpful message to send to Discord
      const appId = event.appId;
      const {
        eventName,
        metricType,
        eventType,
        numSamples,
        thresholdValue,
        thresholdUnit,
        conditionPercentile,
        appVersion,
        violationValue,
        violationUnit,
        investigateUri,
      } = event.data.payload;
      const message = `
    ⚠️ Performance Alert for ${metricType} of ${eventType}: **${eventName}** ⚠️
    
    App id: ${appId}
    Alert condition: ${thresholdValue} ${thresholdUnit}
    Percentile (if applicable): ${conditionPercentile}
    App version (if applicable): ${appVersion}
    
    Violation: ${violationValue} ${violationUnit}
    Number of samples checked: ${numSamples}
    
    **Investigate more:** ${investigateUri}
    `;
```

### Python

```python
    # Construct a helpful message to send to Discord.
    app_id = event.app_id
    perf = event.data.payload
    message = f"""
⚠️ Performance Alert for {perf.metric_type} of {perf.event_type}: **{perf.event_name}** ⚠️

App ID: {app_id}
Alert condition: {perf.threshold_value} {perf.threshold_unit}
Percentile (if applicable): {perf.condition_percentile}
App version (if applicable): {perf.app_version}

Violation: {perf.violation_value} {perf.violation_unit}
Number of samples checked: {perf.num_samples}

**Investigate more:** {perf.investigate_uri}
""".strip()
```

Finally, the function sends the constructed message to Discord through an HTTP
request:

### Node.js

```javascript
const response = await postMessageToDiscord(
    "Firebase Performance Bot", message);
if (response.ok) {
  logger.info(
      `Posted Firebase Performance alert ${eventName} to Discord`,
      event.data.payload,
  );
} else {
  throw new Error(`Discord returned status code ${response.status}`);
}
```

### Python

```python
response = post_message_to_discord(
    "App Performance Bot", message, DISCORD_WEBHOOK_URL.value
)
if response.ok:
    print(f"Posted Firebase Performance alert {perf.event_name} to Discord.")
    pprint.pp(event.data.payload)
else:
    response.raise_for_status()
```

To learn about all the performance alert events that you can capture, go to the
reference documentation for
[Performance Monitoring alerts](https://firebase.google.com/docs/reference/functions/2nd-gen/node/firebase-functions.alerts.performance.md.txt).

### Handle an App Distribution alert event

The example in this section shows you how to write a function for new tester iOS
device alerts.

In this example, the function listens for events that are sent every time a
tester registers a new iOS device. When a new iOS device is registered, you need
to update your provisioning profile with that device's UDID and then
redistribute the app.

### Node.js

```javascript
exports.postnewduuidtodiscord = onNewTesterIosDevicePublished(async (event) => {
```

### Python

```python
@app_distribution_fn.on_new_tester_ios_device_published(secrets=["DISCORD_WEBHOOK_URL"])
def post_new_udid_to_discord(event: app_distribution_fn.NewTesterDeviceEvent) -> None:
    """Publishes a message to Discord whenever someone registers a new iOS test device."""
```

The function then parses the returned object, parsing useful information from the event
payload and constructing a message to post to the Discord channel:

### Node.js

```javascript
  // construct a helpful message to send to Discord
  const appId = event.appId;
  const {
    testerDeviceIdentifier,
    testerDeviceModelName,
    testerEmail,
    testerName,
  } = event.data.payload;
  const message = `
📱 New iOS device registered by ${testerName} <${testerEmail}> for ${appId}

UDID **${testerDeviceIdentifier}** for ${testerDeviceModelName}
`;
```

### Python

```python
    # Construct a helpful message to send to Discord.
    app_id = event.app_id
    app_dist = event.data.payload
    message = f"""
📱 New iOS device registered by {app_dist.tester_name} <{app_dist.tester_email}> for {app_id}

UDID **{app_dist.tester_device_identifier}** for {app_dist.tester_device_model_name}
""".strip()
```

Finally, the function sends the constructed message to Discord through an HTTP
request:

### Node.js

```javascript
const response = await postMessageToDiscord("AppDistribution Bot", message);
if (response.ok) {
  logger.info(
      `Posted iOS device registration alert for ${testerEmail} to Discord`,
  );
} else {
  throw new Error(`Discord returned status code ${response.status}`);
}
```

### Python

```python
response = post_message_to_discord("App Distro Bot", message, DISCORD_WEBHOOK_URL.value)
if response.ok:
    print(f"Posted iOS device registration alert for {app_dist.tester_email} to Discord.")
    pprint.pp(event.data.payload)
else:
    response.raise_for_status()
```

To learn about all the App Distribution alert events that you can capture,
go to the reference documentation for
[App Distribution alerts](https://firebase.google.com/docs/reference/functions/2nd-gen/node/firebase-functions.alerts.appdistribution.md.txt).

To learn how to use a function triggered by an
[in-app feedback Firebase alert from App Distribution](https://firebase.google.com/docs/reference/functions/2nd-gen/node/firebase-functions.alerts.appdistribution.inappfeedbackpayload.md.txt),
see
[Send in-app feedback to Jira](https://github.com/firebase/functions-samples/tree/main/Node/app-distribution-feedback-to-jira).