Using Tera Templates

Tera is the primary templating engine for [[output]] rules. It is ideal for generating JSON output where the structure is straightforward and the data comes directly from the origin_resource and its related graph nodes.

For the complete Tera syntax reference and rescile-specific filters, see Tera Function & Filter Reference and Templating & Data.

Worked Example: Service Summary

This example generates a new service_summary resource for every application that is on the edge network. Each summary is made available as a downloadable JSON file.

data/output/service_summary.toml

origin_resource = "application"

# Define some static data available to the template
output_metadata = { version = "1.1", author = "security-team" }

[[output]]
resource_type = "service_summary"
name = "summary-for-{{ origin_resource.name }}"
filename = "summary-{{ origin_resource.name }}.json"
mimetype = "application/json"
match_on = [
  { property = "network_zone", value = "edge" }
]
# The template uses Tera to generate a JSON object, including conditional logic.
# All variables from the context (`origin_resource`, `output_metadata`) are available.
template = '''
{
  "output_author": "{{ output_metadata.author }}",
  "application_name": "{{ origin_resource.name }}",
  "owner": "{{ origin_resource.has_responsibility[0].node.name }}",
  "hosting_details": {
    "platform": "{{ origin_resource.runs_on[0].node.name }}",
    "criticality": "{% if origin_resource.environment == 'prod' %}"high"{% else %}"low"{% endif %}"
  }
}
'''

• Graph Impact:

  1. The importer finds all application resources that match the match_on criteria (e.g., app-1 and app-2).

  2. It creates a single new resource of type service_summary. This resource’s primary key (name) is also set to service_summary.

  3. For each matching application (app-1, app-2): a. It renders the name template to get the primary key for a new resource (e.g., summary-for-app-1). b. It renders the template, which produces a JSON object string. c. It parses this JSON string. d. It creates a new resource of type service_summary with the generated name. The keys and values from the parsed JSON become the properties of this new resource.

  4. For app-1, a new service_summary resource is created with properties like:

     {
       "name": "summary-for-app-1",
       "filename": "summary-app-1.json",
       "mimetype": "application/json",
       "output_author": "security-team",
       "application_name": "app-1",
       "owner": "team-alpha",
       "hosting_details": { ... }
     }
     

  5. A similar resource is created for app-2.

  6. Finally, a DESCRIBED_BY relationship is created from each matching application (app-1, app-2) to its corresponding new service_summary resource.

Traversing Relationships in Templates

The origin_resource variable exposes related nodes through dot notation. Multi-valued relations are arrays; access a specific item with [0] or iterate with {% for ... %}.

origin_resource = "application"

[[output]]
resource_type = "dependency_report"
name = "deps-{{ origin_resource.name }}"
filename = "deps-{{ origin_resource.name }}.json"
mimetype = "application/json"
template = '''
{
  "application": "{{ origin_resource.name }}",
  "primary_database": "{{ origin_resource.database[0].name | default(value='none') }}",
  "all_databases": {{ origin_resource.database | map(attribute="name") | json_encode | safe }},
  "hosting_platform": "{{ origin_resource.cloud_provider[0].name
                           | default(value=origin_resource.onprem_datacenter[0].name
                           | default(value='unknown')) }}"
}
'''

Tip: Use | default(value="fallback") to avoid rendering errors when a related node does not exist for a particular origin_resource.

Conditional Logic and Loops

Tera’s {% if %} and {% for %} blocks work identically inside template values:

template = '''
{
  "name": "{{ origin_resource.name }}",
  "tier": "{% if origin_resource.environment == 'prod' %}gold{% else %}silver{% endif %}",
  "tags": [
    {% for tag in origin_resource.tags %}
    "{{ tag }}"{% if not loop.last %},{% endif %}
    {% endfor %}
  ]
}
'''

Using Header Variables

Top-level TOML keys defined in the file header are available as template variables alongside origin_resource:

origin_resource = "application"

output_metadata = { version = "2.0", author = "platform-team" }

[[output]]
resource_type = "versioned_summary"
name = "vs-{{ origin_resource.name }}"
filename = "vs-{{ origin_resource.name }}.json"
mimetype = "application/json"
template = '''
{
  "schema_version": "{{ output_metadata.version }}",
  "generated_by":   "{{ output_metadata.author }}",
  "application":    "{{ origin_resource.name }}"
}
'''

For loading data from external JSON files, see Templating & Data — External JSON Files.