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Experimental Gomplate Function Support

· 2 min read
hashfunc
hashfunc
Contributor

Gomplate's experimental functions are now available in Atmos stack manifests. Network calculations can be expressed in stack templates, reducing hardcoded CIDRs and IP addresses across environments.

The Problem​

The net.CIDRSubnets and net.CIDRHost functions calculate subnet CIDRs and host IP addresses from each environment's parent CIDR, reducing hardcoded addresses across stacks. Both functions require Gomplate's experimental mode, but Atmos previously provided no option to enable it in stack templates.

The Fix​

The Gomplate configuration now includes an experimental option for enabling experimental functions in stack templates. It defaults to false and can be set globally or overridden per stack.

Import templates use the global value from atmos.yaml. The option does not apply to document generation or scaffold templates.

How to Use It​

Enable experimental Gomplate functions in your project configuration:

atmos.yaml
templates:
  settings:
    enabled: true
    gomplate:
      enabled: true
      experimental: true

Calculate Subnet CIDRs and Host IP Addresses​

The following stack derives subnet CIDRs and a host IP address from one parent CIDR. It assumes a Terraform component named network with cidr_block, subnet_cidrs, and service_ip inputs:

stacks/deploy/dev.yaml
vars:
  stage: dev

components:
  terraform:
    network:
      vars:
        cidr_block: "10.42.0.0/16"
        subnet_cidrs:
          - "{{ index (net.CIDRSubnets 2 .vars.cidr_block) 0 }}"
          - "{{ index (net.CIDRSubnets 2 .vars.cidr_block) 1 }}"
        service_ip: "{{ net.CIDRHost 10 (index (net.CIDRSubnets 2 .vars.cidr_block) 1) }}"

The call to net.CIDRSubnets 2 adds two prefix bits, splitting the /16 into four /18 subnets. The zero-based index calls select the first two subnets. net.CIDRHost 10 calculates the address at offset 10 in the second subnet. The network inputs resolve to:

cidr_block: 10.42.0.0/16
subnet_cidrs:
  - 10.42.0.0/18
  - 10.42.64.0/18
service_ip: 10.42.64.10

Override per Stack​

To disable experimental functions for a stack while keeping them enabled globally:

Stack manifest
settings:
  templates:
    settings:
      gomplate:
        experimental: false

Stacks inherit the global value when this option is omitted. An explicit false disables experimental functions for that stack, even when they are enabled globally.

Get Involved​

For questions or feedback, please open a GitHub issue.