OpenAI Codex in DevContainers

Overview

OpenAI Codex is OpenAI’s CLI tool for AI-assisted coding. It provides code generation, explanation, and editing capabilities powered by OpenAI’s models, all accessible from your DevContainer terminal.

Installation

Add the OpenAI Codex feature to your devcontainer.json:

{
    "features": {
        "ghcr.io/infrashift/trusted-devcontainer-features/bun:latest": {},
        "ghcr.io/infrashift/trusted-devcontainer-features/openai-codex:latest": {
            "target_version": "latest"
        }
    }
}

The Bun feature is required as a dependency — OpenAI Codex is installed as a global npm package via Bun.

API Key Configuration

OpenAI Codex requires an OpenAI API key. Pass it from your host environment:

{
    "containerEnv": {
        "OPENAI_API_KEY": "${localEnv:OPENAI_API_KEY}"
    }
}

VS Code Extension

The feature automatically recommends the openai.chatgpt VS Code extension for integrated AI assistance within the editor.

CLI Usage

Once inside your DevContainer, use the Codex CLI:

# Start an interactive session
codex

# Ask a direct question
codex "refactor this function to use async/await"

Example Workflows

Code Generation

codex "create a REST API endpoint for user registration with validation"

Code Explanation

codex "explain what the deploy.sh script does step by step"

Refactoring

codex "convert this class component to a functional React component with hooks"

Security Considerations

• API keys: Never commit API keys to version control. Use containerEnv with localEnv references.
• Egress filtering: Pair with the Egress Filter feature to restrict network access to api.openai.com and other required domains.
• Container isolation: Codex runs within the DevContainer boundary and cannot access your host filesystem beyond the mounted workspace.