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!env Function Now Reads from Stack Manifest env Sections

· 3 min read
Erik Osterman
Erik Osterman
Founder @ Cloud Posse

The !env YAML function now supports reading environment variables from env sections defined in your stack manifests and Atmos configuration. This makes it easy to set defaults for environment variables and reference values from your infrastructure configuration.

What's New​

The !env function has been enhanced to check stack manifest env sections before falling back to OS environment variables. This gives you complete control over environment variable resolution in your stack configurations.

How It Works​

The !env function now looks up environment variables in this order:

  1. Component env section from stack manifests (new!)
  2. OS environment variables (fallback)
  3. Default value (if provided in the function call)

This hierarchy gives you maximum flexibility: define defaults in your stack configuration, override with OS environment variables when needed, or provide fallback values inline.

Use Cases​

Setting Environment Variable Defaults​

Define default values for environment variables in your stack manifests:

# stacks/catalog/myapp.yaml
components:
  terraform:
    myapp:
      env:
        LOG_LEVEL: info
        AWS_REGION: us-east-1
        ENVIRONMENT: production
      vars:
        # References the env section above
        log_level: !env LOG_LEVEL
        region: !env AWS_REGION

Referencing Other Environment Variables​

Use the env section to compose environment variables from other stack values:

# stacks/ue1-prod.yaml
components:
  terraform:
    vpc:
      env:
        CLUSTER_NAME: !terraform.output eks prod cluster_name
        VPC_ID: !terraform.output vpc prod vpc_id
      vars:
        # Use env vars in your configuration
        cluster: !env CLUSTER_NAME
        vpc: !env VPC_ID

Providing Fallback Values​

Combine stack defaults with inline fallbacks:

components:
  terraform:
    app:
      env:
        LOG_LEVEL: debug  # Default for this component
      vars:
        # Falls back to 'info' if not in env section or OS env
        log_level: !env LOG_LEVEL info

        # Not defined in env section, uses OS env or fallback
        region: !env AWS_REGION us-west-2

Why This Matters​

This enhancement brings several benefits:

  1. Centralized defaults - Define environment variable defaults once in your stack configuration
  2. Better testability - Override values in stack manifests without changing OS environment
  3. Composition - Reference other Atmos functions in env sections to build complex configurations
  4. Consistency - Same environment variable resolution across all components in a stack
  5. Flexibility - Override stack defaults with OS environment variables when needed

Related Documentation​

Get Started​

Start using env sections in your stack manifests today to centralize your environment variable defaults and improve configuration management. No changes to existing !env usage required - this enhancement is fully backward compatible.

For questions or feedback, join the discussion in our GitHub Discussions.