Epic: Terraform Resources for Dev Containers

Summary

Enable template authors to attach Terraform resources (coder_app, coder_script, coder_env, coder_ai_task) to coder_devcontainer resources, eliminating the need to choose between Dev Containers and our collection of Terraform modules.

Problem Statement

Opting in to Dev Containers requires opting out of our collection of Terraform modules as there is no way of associating terraform resources to the coder_devcontainer resource.

Agents used for Dev Containers are created dynamically after workspace provisioning. Since the sub-agent doesn't exist at Terraform plan/apply time, there is no way to reference it in Terraform.

Solution Overview

Phase 1: Terraform-defined Resources

Introduce a computed subagent_id field on the coder_devcontainer resource that can be referenced by other Terraform resources. This ID is pre-computed at plan time and used when the sub-agent is created at runtime.

resource "coder_devcontainer" "main" {
  agent_id         = coder_agent.main.id
  workspace_folder = "/workspaces/project"
}

resource "coder_app" "code_server" {
  agent_id     = coder_devcontainer.main.subagent_id
  slug         = "code-server"
  display_name = "VS Code"
  url          = "http://localhost:8080"
}

Phase 2: devcontainer.json-defined Resources

Enable Terraform modules to be defined directly in devcontainer.json via customizations.coder.modules, allowing developers to attach modules to their dev container without modifying Terraform templates. The modules are provisioned by coderd using coder/preview.

{
  "customizations": {
    "coder": {
      "modules": {
        "registry.coder.com/coder/code-server/coder:1.0.0": {},
        "registry.coder.com/coder/zed/coder:1": {
          "folder": "/home/coder/coder"
        }
      }
    }
  }
}

The key format is <registry link>:<version> and the value is an object of key-value mappings where each key is translated into a Terraform variable.