Atmos Templates

Atmos Go Templates

Overview

Go templates use {{ }} delimiters and are processed before YAML parsing. They support the full Go text/template syntax plus Sprig and Gomplate function libraries.

Go templates are an escape hatch for complex conditional logic, loops, dynamic key generation, or advanced string manipulation that YAML functions cannot handle. For most use cases, prefer YAML functions (see the atmos-yaml-functions skill).

Enabling Go Templates

# atmos.yaml
templates:
  settings:
    enabled: true
    evaluations: 1      # Number of processing passes
    delimiters: ["{{", "}}"]  # Default delimiters
    sprig:
      enabled: true     # Enable Sprig functions
    gomplate:
      enabled: true     # Enable Gomplate functions and datasources
      timeout: 5        # Datasource timeout in seconds

Template Context Variables

In Go templates, you can reference any value from the component's configuration (as returned by atmos describe component):

Template Examples

components:
  terraform:
    vpc:
      vars:
        tags:
          atmos_component: "{{ .atmos_component }}"
          atmos_stack: "{{ .atmos_stack }}"
          terraform_workspace: "{{ .workspace }}"
          # Sprig function
          provisioned_by: '{{ env "USER" }}'
          # Gomplate function
          description: "{{ strings.Title .atmos_component }} in {{ .atmos_stack }}"

atmos.Component Template Function

Reads any section or attribute from another component's configuration, including Terraform outputs:

vars:
  # Read outputs (remote state)
  vpc_id: '{{ (atmos.Component "vpc" .stack).outputs.vpc_id }}'

  # Read variables from another component
  vpc_name: '{{ (atmos.Component "vpc" .stack).vars.name }}'

  # Read settings
  test_setting: '{{ (atmos.Component "test" .stack).settings.test }}'

  # Read metadata
  component_name: '{{ (atmos.Component "test" .stack).metadata.component }}'

  # Complex outputs require !template + toJson
  subnet_ids: !template '{{ toJson (atmos.Component "vpc" .stack).outputs.private_subnet_ids }}'

atmos.GomplateDatasource Template Function

Fetches external data with automatic caching:

settings:
  templates:
    settings:
      gomplate:
        datasources:
          ip:
            url: "https://api.ipify.org?format=json"
          secret:
            url: "aws+smp:///path/to/secret"

vars:
  public_ip: '{{ (atmos.GomplateDatasource "ip").ip }}'
  db_password: '{{ (atmos.GomplateDatasource "secret").password }}'

The function caches results per execution -- multiple references to the same datasource make only one external call.

atmos.Store Template Function

Reads from stores using Go template syntax (same as !store YAML function but in template form):

vars:
  vpc_id: '{{ atmos.Store "prod/ssm" .stack "vpc" "vpc_id" }}'
  config: !template '{{ (atmos.Store "redis" .stack "config" "config_map").defaults | toJSON }}'

Template Evaluations (Processing Pipelines)

Atmos supports multiple evaluation passes for template processing:

# atmos.yaml
templates:
  settings:
    enabled: true
    evaluations: 2  # Two passes

With multiple evaluations, output from the first pass becomes input to the second pass. This is useful for:

• Combining templates from different sections
• Using templates in datasource URLs
• Multi-stage template resolution

Excluding Templates from Processing

Passing Templates to External Tools

Use the backtick escape or !literal to prevent Atmos from processing templates intended for external systems (ArgoCD, Helm, Datadog):

# Using !literal (recommended, see atmos-yaml-functions skill)
annotation: !literal "{{ .Values.ingress.class }}"

# Using backtick escape
annotation: "{{`{{ .Values.ingress.class }}`}}"

# Using printf
annotation: '{{ printf "{{ .Values.ingress.class }}" }}'

Templates in Imports

When using Go templates in both imports and stack manifests, templates intended for the second pass (stack processing) must be escaped in the import file:

# stacks/catalog/eks/eks_cluster.tmpl
components:
  terraform:
    eks/cluster:
      vars:
        # First pass: resolved from import context
        enabled: "{{ .enabled }}"
        name: "{{ .name }}"
        tags:
          # Second pass: escaped for stack processing
          atmos_component: "{{`{{ .atmos_component }}`}}"
          atmos_stack: "{{`{{ .atmos_stack }}`}}"

Template Configuration in Stack Manifests

Template settings can be defined in settings.templates.settings in stack manifests, which deep-merges with templates.settings in atmos.yaml. Stack manifest settings take precedence.

# stacks/orgs/acme/_defaults.yaml
settings:
  templates:
    settings:
      env:
        AWS_PROFILE: "my-profile"
      gomplate:
        timeout: 7
        datasources:
          config:
            url: "./my-config.json"

Note: enabled, sprig.enabled, gomplate.enabled, evaluations, and delimiters settings are not supported in stack manifests (only in atmos.yaml).

When to Use Go Templates vs. YAML Functions

Performance Best Practices

1. Prefer YAML functions over Go templates -- Type-safe, cannot break YAML
2. Prefer !store over atmos.Component for outputs -- Avoids Terraform initialization
3. Use atmos.GomplateDatasource instead of datasource -- Built-in caching prevents redundant API calls
4. Minimize atmos.Component usage -- Each call may initialize Terraform
5. All template functions cache results per execution for repeated calls.

Common Pitfalls

1. Go templates break YAML -- Unquoted {{ }} can cause YAML parse errors. Always quote template expressions.
2. Type confusion -- Go templates always return strings. Use !template with toJson for complex types.
3. Indentation issues -- Multi-line template output can break YAML indentation.
4. Sprig/Gomplate conflicts -- The env function exists in both libraries with different syntax. Use getenv for Gomplate's version when both are enabled.
5. Performance degradation -- Overuse of atmos.Component or !terraform.output across many stacks can dramatically slow atmos describe stacks and atmos describe affected.

Additional Resources

• For complete Go template context variables and functions, see references/go-templates.md
• For YAML functions (!terraform.state, !store, !env, etc.), see the atmos-yaml-functions skill