# Submodule

> An OpenTofu module used as a child within another module rather than deployed directly.

A *submodule* is an OpenTofu/Terraform module that is called as a child module within another module rather than being deployed directly via Terragrunt. Submodules are composed into larger modules using `module` blocks in HCL.

In the Panfactum stack, submodules are a key mechanism for code reuse. Panfactum provides many submodules (such as `kube_pod`, `kube_service`, etc.) that encapsulate common infrastructure patterns and can be imported into first-party modules.

Unlike root modules, submodules:

- Do not have their own Terraform state
- Do not declare provider configurations (these are inherited from the parent)
- Cannot be deployed standalone via Terragrunt

When using Panfactum submodules in first-party code, use the `pf_module_source` and `pf_module_ref` variables to ensure the submodule version automatically tracks the deployed Panfactum Stack version.