Use Mustache Templates in Runbook Actions

Learn how to use Mustache templates in runbook actions for dynamic content in Harness AI SRE.

Mustache templates provide simple variable substitution in runbook actions. Use Mustache when you need to insert dynamic values from incidents, alerts, or previous action outputs into your runbook actions.

How to reference fields

When configuring runbook actions in the UI:

1. Click an action input field that supports dynamic values (marked with a data picker icon)

2. Click the data picker button (looks like a database icon)

3. Select the field source:

   • Incident - Fields from the current incident

   • Alert - Fields from the triggering alert

   • Runbook Inputs - Variables defined in the Input/Output section

   • Action Outputs - Results from previous actions

4. Select the specific field

5. The Mustache variable is automatically inserted: {{incident.service}}

Alternatively, you can type Mustache syntax directly: {{incident.field_name}}

---

Example: Slack message with incident details

Action: Slack: Post Message

Channel: #incidents

Message (configured in form field):

🔥 **New {{incident.severity}} Incident**

**Title**: {{incident.title}}
**Service**: {{incident.service}}
**Environment**: {{incident.environment}}
**Owner**: {{incident.owner}}
**Status**: {{incident.status}}

**View Details**: {{incident.url}}

Result: When the runbook runs, Mustache variables are replaced with actual values:

🔥 **New SEV1 Incident**

**Title**: Payment Service High Error Rate
**Service**: payment-service
**Environment**: production
**Owner**: Jane Smith
**Status**: investigating

**View Details**: https://app.harness.io/incidents/INC-456

CEL alternative with conditional logic:

${{incident.severity in ["0", "1"] ? "🚨🚨🚨" : "🔥"}}
**New ${{
  incident.severity == "0" ? "CRITICAL" : "SEV" + incident.severity
}} Incident**

**Title**: ${{incident.title}}
**Service**: ${{incident.service}}
**Environment**: ${{
  incident.environment == "production" ?
  "🔴 PRODUCTION" : incident.environment
}}
**Owner**: ${{
  incident.owner != null ? incident.owner : "⚠️ UNASSIGNED"
}}
**Status**: ${{incident.status}}
**Priority**: ${{
  incident.severity in ["0", "1"] ?
  "IMMEDIATE ACTION REQUIRED" : "Normal triage"
}}

**View Details**: ${{incident.url}}

---

Example: Conditional routing for Slack

Use runbook triggers to create conditional behavior based on field values.

Pattern: Route P1 alerts to #critical-incidents, others to #incidents

Implementation:

1. Create two runbooks:

   • P1 Alert Handler:

     • Trigger: Alert created with alert.priority equals p1_critical

     • Action: Slack post to #critical-incidents

   • Standard Alert Handler:

     • Trigger: Alert created with alert.priority in [p2_error, p3_warning, p4_info]

     • Action: Slack post to #incidents

Go to Create runbook triggers to configure conditional execution.

---

Example: Jira ticket with incident context

Action: Jira: Create Issue

Form Configuration:

• Project: INCIDENT (static value)

• Issue Type: Incident (static value)

• Summary (form field with data picker):

  [{{incident.severity}}] {{incident.title}}

• Description (form field with data picker):

  Incident Details:
  - **Service**: {{incident.service}}
  - **Environment**: {{incident.environment}}
  - **Severity**: {{incident.severity}}
  - **Status**: {{incident.status}}
  - **Created**: {{incident.created_at}}
  
  View in AI SRE: {{incident.url}}

• Priority (form field with data picker):

  {{incident.severity}}

Result: Jira ticket is created with all incident context embedded.

CEL alternative with dynamic priority logic:

Summary field:

[${{
  incident.severity == "0" ? "P0-CRITICAL" :
  incident.severity == "1" ? "P1-HIGH" : "P2"
}}] ${{incident.title}}

Description field:

Incident Details:
- **Service**: ${{incident.service}}
- **Environment**: ${{
    incident.environment == "production" ?
    "🔴 PRODUCTION" : incident.environment
  }}
- **Severity**: SEV${{incident.severity}} (${{
    incident.severity == "0" ? "Critical outage" :
    incident.severity == "1" ? "Major incident" :
    "Moderate issue"
  }})
- **Status**: ${{incident.status}}
- **Created**: ${{incident.created_at}}

${{
  incident.affected_users != null &&
  incident.affected_users > 0 ?
  "**User Impact**: " + string(incident.affected_users) +
  " users affected\n" : ""
}}

**Required Actions**:
${{
  incident.severity in ["0", "1"] ?
  "- Page on-call team IMMEDIATELY\n- Start incident bridge\n- Update status page" :
  "- Assign to service team\n- Triage within SLA"
}}

View in AI SRE: ${{incident.url}}

---

Example: HTTP request with alert data

Action: HTTP Request

Form Configuration:

• URL (form field):

  https://api.example.com/alerts/{{alert.id}}/acknowledge

• Method: POST (dropdown)

• Body (form field with data picker):

  {
    "alert_id": "{{alert.id}}",
    "service": "{{alert.service}}",
    "priority": "{{alert.priority}}",
    "acknowledged_by": "AI SRE Runbook"
  }

---

Example: Reference previous action outputs

Actions can reference outputs from previous actions in the same runbook.

Action 1: Zoom: Create Meeting

• Outputs: join_url, meeting_id, passcode

Action 2: Slack: Post Message

• Message (referencing Action 1 output):

  🎥 **Incident Bridge Created**
  
  Join the call:
  {{runbook.outputs.zoom_create_meeting.join_url}}
  Meeting ID:
  {{runbook.outputs.zoom_create_meeting.meeting_id}}
  Passcode:
  {{runbook.outputs.zoom_create_meeting.passcode}}
  
  **Incident**: {{incident.title}}

The data picker automatically shows available outputs from previous actions.

---

Next steps

• Go to Use CEL in runbook actions to implement conditional logic and transformations.

• Go to Use system fields in runbook actions to learn about available system fields.

• Go to Best practices to review field usage guidelines.