A **development container** is a running [Docker](https://www.docker.com) container with a well-defined tool/runtime stack and its prerequisites. You can try out development containers with **[GitHub Codespaces](https://github.com/features/codespaces)** or **[Visual Studio Code Remote - Containers](https://aka.ms/vscode-remote/containers)**.
This is a sample project that lets you try out either option in a few easy steps. We have a variety of other [vscode-remote-try-*](https://github.com/search?q=org%3Amicrosoft+vscode-remote-try-&type=Repositories) sample projects, too.
Follow these steps to open this sample in a Codespace:
1. Click the Code drop-down menu and select the **Open with Codespaces** option.
1. Select **+ New codespace** at the bottom on the pane. If you don't own the repo, this will create a fork of this repository under your account.
For more info, check out the [GitHub documentation](https://docs.github.com/en/free-pro-team@latest/github/developing-online-with-codespaces/creating-a-codespace#creating-a-codespace).
### VS Code Remote - Containers
Follow these steps to open this sample in a container using the VS Code Remote - Containers extension:
1. If this is your first time using a development container, please ensure your system meets the pre-reqs (i.e. have Docker installed) in the [getting started steps](https://aka.ms/vscode-remote/containers/getting-started).
- Choose the "Python" sample, wait for the container to start, and try things out!
> **Note:** Under the hood, this will use the **Remote-Containers: Clone Repository in Container Volume...** command to clone the source code in a Docker volume instead of the local filesystem. [Volumes](https://docs.docker.com/storage/volumes/) are the preferred mechanism for persisting container data.
> **Note:** This container runs as a non-root user with sudo access by default. Comment out `"remoteUser": "vscode"` in `.devcontainer/devcontainer.json` if you'd prefer to run as root.
- Notice that the Python extension is already installed in the container since the `.devcontainer/devcontainer.json` lists `"ms-python.python"` as an extension to install automatically when the container is created.
> **Tip:** If you use this container outside of VS Code via `docker run` with `-p 9000`, you may need to append `--host 0.0.0.0` to the command above. The `-p` option "publishes" the port rather than forwarding it. It therefore will not work if the application only listens to localhost. The `forwardPorts` property in `devcontainer.json` does not have this limitation, but you can use `appPort` property instead if you want to mirror the `docker run` behavior.
- Continue (<kbd>F5</kbd>). You can connect to the server in the container by either: clicking on `Running on http://0.0.0.0:9000/` in the terminal output, or "Open in Browser" next to port 9000 in the 'Ports' view (you can get to the 'Ports' view by clicking on the "1" in the status bar, which means your app has 1 forwarded port).
> **Note:** In Remote - Containers, you can access your app at `http://localhost:9000` in a local browser. But in a browser-based Codespace, you must click the link from the terminal output or the `Ports` view so that the service handles port forwarding in the browser and generates the correct URL.
4.**Rebuild or update your container** (*Currently, only containers with the VS Code Remote - Containers extension can be rebuilt.*)
You may want to make changes to your container, such as installing a different version of a software or forwarding a new port. You'll rebuild your container for your changes to take effect.
**Forward a port statically:** As an example change, let's forward a port statically in the `.devcontainer/devcontainer.json` file.
> **Note:** Remote-Containers and Codespaces also take care of dynamic port forwarding, but there may be instances in which we want to statically declare a forwarded port.
- Open the `.devcontainer/devcontainer.json` file.
- Uncomment the `forwardedPorts` attribute and adjust the port number as needed.
- Press <kbd>F1</kbd> and select the **Remote-Containers: Rebuild Container** command so the modifications are picked up.
