At CodeSandbox, we use Tailscale (opens in a new tab) to manage network access for private resources, including some of the services that make up CodeSandbox. As you work on an application in CodeSandbox Repositories, you might want to grant it access to private resources on your network. Tailscale can help.

You can try Tailscale for free by following their Quickstart guide (opens in a new tab). Throughout this documentation, we'll assume you have a tailnet called (which you should replace with your name (opens in a new tab)).


Many applications exist as part of a collection of services. Sometimes we can isolate an application from other services during development, but this isn't always possible. Just because you develop in CodeSandbox, however, doesn't mean you can't connect your application to private services running in your organization's network.

Integrating with Tailscale provides containers running in a CodeSandbox Repository environment with access to your private resources. Combined with Tailscale's MagicDNS and ACLs, you can develop your application as if it were hosted in the same network as your other services — without compromising security.

Creating an Auth Key

Integrating a CodeSandbox Repository with Tailscale requires an auth key (opens in a new tab), a secret you embed in the CodeSandbox environment to allow registration on your network. Admins can create them on the auth key page (opens in a new tab) of the Tailscale admin console.

The auth key you give to CodeSandbox should be:

  • Reusable, so you don't encounter issues when forking a new branch,
  • Ephemeral, so you don't have to clean up old branches from your tailnet, and
  • Pre-authorized, so you don't have to wait for someone to approve a new branch before you start developing.

Depending on your tailnet setup, you may also want it to be:

  • Tagged, so CodeSandbox environments are automatically labeled and access-controlled via Tailscale's ACLs.

Setting up your Repository

Tailscale currently works in CodeSandbox Repository environments by adding a container to a Dockerized application setup (for example, using docker-compose). The additional container runs the Tailscale client and provides networking for the other containers.

Environment Variables

Before launching the new container, it is necessary to add the Tailscale auth key as an environment variable. With a branch open in the Repository editor, go to the CodeSandbox menu, and choose Env variables. Throughout the rest of this documentation, we will assume you named the variable TS_AUTHKEY. Restart any existing branches to update the running environment.

Docker Container

In a setup using Docker Compose, we can add the tailscale image (opens in a new tab) as an additional service beside our application. Here's an example docker-compose.yml file with the Tailscale service:

    image: tailscale/tailscale
      - net_admin
      - net_raw
      - sys_module
    command: "tailscaled --state=mem:"
      - "/dev/net/tun:/dev/net/tun"
    # ...
    network_mode: service:tailscale

This runs the latest tailscale image with a few customizations. Then, it instructs the application container to use the Tailscale container's network using network_mode.

After this setup, docker-compose up will start the application and Tailscale containers, but it will not immediately initiate a connection. For this, a separate command is necessary:

docker-compose exec tailscale tailscale up --authkey=${TS_AUTHKEY} --accept-routes --hostname=csb-${HOSTNAME}

Luckily, both of these steps can be automated. The following example .codesandbox/tasks.json runs each of these commands as tasks every time a new branch is created:

  "$schema": "",
  "tasks": {
    "docker-compose up": {
      "name": "Docker Compose",
      "command": "docker-compose up",
      "restartOn": {
        "branch": true
      "runAtStart": true
    "tailscale": {
      "name": "Connect Tailscale",
      "command": "docker-compose exec tailscale tailscale up --accept-routes --authkey=${TS_AUTHKEY} --hostname=csb-${HOSTNAME}",
      "restartOn": {
        "branch": true
      "runAtStart": true

Putting all of this together, CodeSandbox will automatically start your application using Docker Compose, include a Tailscale container, and initiate a connection based on your Auth Key. The running application will have access to private resources on your tailnet.

If you enjoy using CodeSandbox and Tailscale, and would like to see deeper integration between these products in the future, please let us know using our contact form (opens in a new tab)!