Dockerfile reference

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Customize the sandbox container image with your own packages, tools, and configurations by extending the base runtime image.

Base images

The Sandbox SDK provides multiple image variants. All except -musl are based on Ubuntu. Choose the one that fits your use case:

# Default - lean, no Python
FROM docker.io/cloudflare/sandbox:0.12.14

# Python - includes Python 3.11 + data science packages
FROM docker.io/cloudflare/sandbox:0.12.14-python

# OpenCode - includes OpenCode CLI for AI coding
FROM docker.io/cloudflare/sandbox:0.12.14-opencode

# musl - minimal Alpine image, no Node.js, Bun, or Python
FROM docker.io/cloudflare/sandbox:0.12.14-musl

:::caution[Version synchronization required] Always match the Docker image version to your npm package version. If you are using @cloudflare/sandbox@0.12.14, use docker.io/cloudflare/sandbox:0.12.14 (or variant) as your base image.

Why this matters: The SDK automatically checks version compatibility on startup. Mismatched versions can cause features to break or behave unexpectedly. If versions don't match, you'll see warnings in your logs.

See Version compatibility for troubleshooting version mismatch warnings. :::

Default image

The default image is optimized for JavaScript and TypeScript workloads:

• Ubuntu 22.04 LTS base
• Node.js 22 LTS with npm
• Bun 1.x (JavaScript/TypeScript runtime)
• System utilities: curl, wget, git, jq, zip, unzip, file, procps, ca-certificates

Python image

The -python variant includes everything in the default image plus:

• Python 3.11 with pip and venv
• Pre-installed packages: matplotlib, numpy, pandas, ipython

OpenCode image

The -opencode variant includes everything in the default image plus:

• OpenCode CLI for AI-powered coding agents

musl image

The -musl variant is a minimal image:

• Alpine Linux 3.21 base
• Git, curl, and bash
• No Node.js, Bun, or Python

Its sandbox binary is built for musl, so it also runs in other Alpine-based images. Docker in Docker copies it into docker:dind.

Creating a custom image

Create a Dockerfile in your project root:

FROM docker.io/cloudflare/sandbox:0.12.14-python

# Install additional Python packages
RUN pip install --no-cache-dir \
    scikit-learn==1.3.0 \
    tensorflow==2.13.0 \
    transformers==4.30.0

# Install Node.js packages globally
RUN npm install -g typescript ts-node prettier

# Install system packages
RUN apt-get update && apt-get install -y \
    postgresql-client \
    redis-tools \
    && rm -rf /var/lib/apt/lists/*

Update wrangler.jsonc to reference your Dockerfile:

{
	"containers": [
		{
			"class_name": "Sandbox",
			"image": "./Dockerfile",
		},
	],
}

When you run wrangler dev or wrangler deploy, Wrangler automatically builds your Docker image and pushes it to Cloudflare's container registry. You don't need to manually build or publish images.

Using arbitrary base images

You can add sandbox capabilities to any Docker image using the standalone binary. This approach lets you use your existing images without depending on the Cloudflare base images:

FROM your-custom-image:tag

# Copy the sandbox binary from the official image
COPY --from=docker.io/cloudflare/sandbox:0.12.14 /container-server/sandbox /sandbox

ENTRYPOINT ["/sandbox"]

The /sandbox binary starts the HTTP API server that enables SDK communication. You can optionally run your own startup command:

FROM node:22-slim

COPY --from=docker.io/cloudflare/sandbox:0.12.14 /container-server/sandbox /sandbox

# Copy your application
COPY . /app
WORKDIR /app

ENTRYPOINT ["/sandbox"]
CMD ["node", "server.js"]

When using CMD, the sandbox binary runs your command as a child process with proper signal forwarding.

Custom startup scripts

For more complex startup sequences, create a custom startup script:

FROM docker.io/cloudflare/sandbox:0.12.14-python

COPY my-app.js /workspace/my-app.js
COPY startup.sh /workspace/startup.sh
RUN chmod +x /workspace/startup.sh

CMD ["/workspace/startup.sh"]

The base image already sets the correct ENTRYPOINT, so you only need to provide a CMD. The sandbox binary starts the HTTP API server, then spawns your CMD as a child process with proper signal forwarding.

#!/bin/bash

# Start your services in the background
node /workspace/my-app.js &

# Start additional services
redis-server --daemonize yes
until redis-cli ping; do sleep 1; done

# Keep the script running (the sandbox binary handles the API server)
wait

:::note[Legacy startup scripts] If you have existing startup scripts that end with exec bun /container-server/dist/index.js, they will continue to work for backwards compatibility. However, we recommend migrating to the new approach using CMD for your startup script. Do not override ENTRYPOINT when extending the base image. :::

Related resources

• Image Management - Building and pushing images to Cloudflare's registry
• Wrangler configuration - Using custom images in wrangler.jsonc
• Docker documentation - Complete Dockerfile syntax
• Container concepts - Understanding the runtime environment