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Use Mustache Templates in Webhooks

Use Mustache templates to map webhook payload fields to alert fields in Harness AI SRE.

When to Use Mustache in Webhooks​

Mustache templates are used for field mapping (populating alert field values) after a webhook is accepted. This is different from CEL expressions, which are used for filtering (deciding whether to create an alert).

Use Mustache for:

  • Mapping webhook payload fields to alert fields
  • Simple variable substitution
  • Transforming webhook data into alert data

Use CEL for:

  • Filtering which webhooks create alerts
  • Conditional logic before alert creation
  • Complex boolean expressions

Note: CEL is used for filtering (deciding whether to create an alert), while Mustache is used for mapping (populating alert field values). They serve different purposes in the webhook processing pipeline.

Field Mapping with Mustache​

After parsing your webhook payload in the visual builder, reference fields using Mustache templates:

Basic Field Mapping​

# Map webhook fields to alert fields
title: "{{webhook.alert_name}}"
description: "{{webhook.message}}"
severity: "{{webhook.severity}}"
service: "{{webhook.service}}"
environment: "{{webhook.environment}}"

Nested Field Access​

# Access nested JSON fields
title: "{{webhook.alert.name}}"
service: "{{webhook.metadata.service}}"
region: "{{webhook.location.region}}"

Example: Datadog Webhook Mapping​

title: "{{webhook.title}}"
description: "{{webhook.body}}"
severity: "{{webhook.alert_type}}"
service: "{{webhook.tags[0]}}"
priority: "{{webhook.alert_priority}}"

Example: Custom Application Webhook​

title: "Alert from {{webhook.source}}"
description: "{{webhook.message}}"
severity: "{{webhook.level}}"
service: "{{webhook.app_name}}"
environment: "{{webhook.env}}"

Best Practices​

1. Use Descriptive Field Names​

# ✅ Clear mapping
title: "{{webhook.alert_title}}"
service: "{{webhook.service_name}}"

# ❌ Unclear mapping
title: "{{webhook.t}}"
service: "{{webhook.s}}"

2. Provide Fallback Values​

If your webhook payload might not always include certain fields, test with sample payloads to ensure the mapping works correctly.

3. Map All Required Fields​

Ensure you map all required alert fields from your webhook payload:

  • title - Alert title
  • severity - Alert severity level
  • service - Affected service (if applicable)

4. Test Your Mappings​

  1. Send a test webhook payload
  2. Verify alert fields are populated correctly
  3. Check for missing or incorrectly mapped values
  4. Adjust mappings as needed

Combined with CEL Filtering​

You can use CEL for filtering and Mustache for mapping in the same webhook:

Step 1: CEL filters the webhook

webhook.priority == "P1" && webhook.environment == "production"

Step 2: Mustache maps accepted webhooks to alerts

title: "{{webhook.alert_name}}"
description: "{{webhook.message}}"
severity: "{{webhook.severity}}"

Common Patterns​

Pattern 1: Monitor Tool Integration​

# Generic monitoring tool mapping
title: "{{webhook.alert_title}}"
description: "{{webhook.alert_description}}"
severity: "{{webhook.alert_severity}}"
service: "{{webhook.service_name}}"
source: "{{webhook.source_system}}"

Pattern 2: Application Error Tracking​

# Application error webhook
title: "{{webhook.error_type}} in {{webhook.app_name}}"
description: "{{webhook.error_message}}"
severity: "critical"
service: "{{webhook.app_name}}"
environment: "{{webhook.deployment_env}}"

Pattern 3: Infrastructure Monitoring​

# Infrastructure alert
title: "{{webhook.resource_type}} {{webhook.resource_name}} {{webhook.status}}"
description: "{{webhook.details}}"
severity: "{{webhook.severity_level}}"
service: "{{webhook.service_tag}}"
region: "{{webhook.region}}"

Complete Payload and Mapping Examples​

Example 1: Generic Alert Format​

Incoming webhook payload:

{
  "alert": {
    "name": "High CPU Usage",
    "severity": "critical",
    "message": "CPU usage above 90%",
    "timestamp": "2024-01-15T10:30:00Z"
  },
  "metadata": {
    "service": "payment-api",
    "environment": "production",
    "team": "platform"
  },
  "metrics": {
    "cpu_usage": 95.5,
    "memory_usage": 85.2
  }
}

Field mapping:

title: "{{webhook.alert.name}}"
description: "{{webhook.alert.message}}"
severity: "{{webhook.alert.severity}}"
service: "{{webhook.metadata.service}}"
environment: "{{webhook.metadata.environment}}"

Result: Creates alert with title "High CPU Usage", description "CPU usage above 90%", severity "critical", service "payment-api", environment "production".

Example 2: Monitoring System Format​

Incoming webhook payload:

{
  "monitor": {
    "id": "mon_12345",
    "status": "ALERT",
    "priority": "P1"
  },
  "resource": {
    "name": "payments-prod-api",
    "type": "kubernetes_pod",
    "namespace": "production"
  },
  "data": {
    "threshold": 90,
    "current_value": 95.5,
    "duration": "5m"
  }
}

Field mapping:

title: "{{webhook.resource.type}} {{webhook.resource.name}} alert"
description: "Monitor {{webhook.monitor.id}}: {{webhook.resource.type}} exceeded threshold"
severity: "{{webhook.monitor.priority}}"
service: "{{webhook.resource.name}}"
environment: "{{webhook.resource.namespace}}"

Result: Creates alert with title "kubernetes_pod payments-prod-api alert", service "payments-prod-api", environment "production", severity "P1".

Example 3: Custom Application Format​

Incoming webhook payload:

{
  "application": "order-service",
  "alert_type": "business_logic",
  "details": {
    "error": "Database connection timeout",
    "impact": "Order processing delayed",
    "affected_regions": ["us-west-1", "us-east-1"]
  },
  "context": {
    "datacenter": "aws-us-west",
    "component": "order-processor"
  }
}

Field mapping:

title: "{{webhook.alert_type}} error in {{webhook.application}}"
description: "{{webhook.details.error}} - Impact: {{webhook.details.impact}}"
severity: "critical"
service: "{{webhook.application}}"
environment: "{{webhook.context.datacenter}}"

Result: Creates alert with title "business_logic error in order-service", description "Database connection timeout - Impact: Order processing delayed", service "order-service".

Next steps​

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Need Help? Contact our support team by email at support@harness.io or visit the Harness Documentation for additional resources and troubleshooting guides.