feat(docs): add guide for configuring Tailscale with Scalingo

src/_posts/platform/app/2000-01-01-tailscale.md

@@ -0,0 +1,101 @@
+---
+layout: page
+title: Configure Tailscale
+modified_at: 2026-01-05 00:00:00
+tags: tailscale networking vpn buildpack
+---
+
+[Tailscale](https://tailscale.com/) is a zero-config VPN that creates a secure network between your servers, computers, and cloud instances. This guide explains how to connect your application container on Scalingo to your Tailscale network.
+
+## Prerequisites
+
+* A Tailscale account.
+* A [Tailscale Auth Key](https://tailscale.com/kb/1085/auth-keys/).
+
+## Step 1: Multi-buildpack Configuration
+
+To install Tailscale and your application dependencies, you need to use the [multi-buildpack]({% post_url platform/deployment/buildpacks/2000-01-01-multi %}).
+
+Create or update the `.buildpacks` file at the root of your repository:
+
+```text
+https://github.com/Scalingo/apt-buildpack.git
+# Add any other buildpack required to build your application (e.g. scalingo/nodejs, scalingo/ruby, etc.)
+```
+
+## Step 2: Aptfile Configuration
+
+The [APT buildpack]({% post_url platform/deployment/buildpacks/2000-01-01-apt %}) allows you to install additional packages. Create a file named `Aptfile` at the root of your repository with the following content:
+
+```text
+wget
+curl
+tailscale
+:repo:deb [trusted=yes] https://pkgs.tailscale.com/stable/ubuntu [dist] main
+```
+
+Replace `[dist]` with the codename of the [stack]({% post_url platform/internals/stacks/2000-01-01-stacks %}) you are using:
+* `noble` for `scalingo-24` (default)
+* `jammy` for `scalingo-22`
+* `focal` for `scalingo-20`
+
+## Step 4: Set TAILSCALE_AUTHKEY Environment Variable
+
+You need to provide your Tailscale Auth Key to your application via an [environment variable]({% post_url platform/app/2000-01-01-environment %}).
+
+1. Generate an auth key in your [Tailscale admin console](https://login.tailscale.com/admin/settings/keys).
+2. Set the `TAILSCALE_AUTHKEY` environment variable on your Scalingo application:
+
+```bash
+scalingo --app my-app env-set TAILSCALE_AUTHKEY=tskey-auth-ok...
+```
+
+## Step 4: .profile Configuration
+
+The `.profile` script is executed before your application starts ([see dedicated page]({% post_url platform/internals/2000-01-01-container-management %}#the-profile-script)). It will be used to start the Tailscale daemon and connect to your network.
+
+Create a file named `.profile` at the root of your repository:
+
+```bash
+#!/bin/bash
+tailscaled --tun=userspace-networking --socks5-server=localhost:1055 --socket /tmp/tailscaled.sock &
+tailscale --socket /tmp/tailscaled.sock up --auth-key=$TAILSCALE_AUTHKEY
+```
+
+## Step 5: Deploy Your Application
+
+Deploy your application by pushing your changes to Scalingo:
+
+```bash
+git add .buildpacks Aptfile .profile
+git commit -m "Configure Tailscale"
+git push scalingo master
+```
+
+During the deployment, you should see:
+* The installation of Tailscale in the deployment logs.
+* The connection to Tailscale in the application logs.
+* Your Scalingo application appearing in your [Tailscale console](https://login.tailscale.com/admin/machines).
+
+## Step 6: Test the Connection
+
+You can verify the connection by running a [one-off container]({% post_url platform/app/2000-01-01-tasks %}).
+
+1. Start a one-off container:
+   ```bash
+   scalingo --app my-app run bash
+   ```
+
+2. In the container, set the `ALL_PROXY` environment variable to use the local Tailscale proxy:
+   ```bash
+   export ALL_PROXY=socks5://localhost:1055/
+   ```
+
+3. Test the connection to another service in your Tailscale network:
+   ```bash
+   curl [host]:[port]/_health
+   ```
+
+{% note %}
+The `ALL_PROXY` environment variable directs software that respects it (like `curl`) to use the local SOCKS5 proxy provided by Tailscale.
+{% endnote %}