Add a dev container to your project

The default codespaces container will support running Node.js projects like vscode-remote-try-node out of the box. By setting up a custom container you can customize the tools and scripts that run as part of codespace creation and ensure a fully reproducible environment for all Codespaces users in your repository.

To set up your project with a custom container, you will need to use a devcontainer.json file to define the environment. In Codespaces you can add this either from a template or you can create your own. For more information on dev containers, see "Introduction to dev containers".

1. Access the Command Palette (Shift + Command + P / Ctrl + Shift + P), then start typing "dev container". Select Codespaces: Add Development Container Configuration Files....
2. For this example, click Node.js. If you need additional features you can select any container that’s specific to Node or a combination of tools such as Node and MongoDB.
3. Click the recommended version of Node.js.
4. Select any additional features to install and click OK.
5. Access the command palette (Shift + Command + P/ Ctrl + Shift + P), then start typing "rebuild". Select Codespaces: Rebuild Container.

Adding the Node.js dev container template adds a .devcontainer folder to the root of your project's repository with the following files:

• devcontainer.json
• Dockerfile

The newly added devcontainer.json file defines a few properties that are described below.

name - You can name your dev container anything, this is just the default.

build - The build properties.

• dockerfile - In the build object, dockerfile is a reference to the Dockerfile that was also added from the template.
• args
  • VARIANT: This file only contains one build argument, which is the node variant we want to use that is passed into the Dockerfile.

settings - These are Visual Studio Code settings that you can set.

• terminal.integrated.shell.linux - While bash is the default here, you could use other terminal shells by modifying this.

extensions - These are extensions included by default.

• dbaeumer.vscode-eslint - ES lint is a great extension for linting, but for JavaScript there are a number of great Marketplace extensions you could also include.

forwardPorts - Any ports listed here will be forwarded automatically.

postCreateCommand - If you want to run anything after you land in your codespace that’s not defined in the Dockerfile, you can do that here.

remoteUser - By default, you’re running as the vscode user, but you can optionally set this to root.

You can use the Dockerfile to add additional container layers to specify OS packages, node versions, or global packages we want included in our Dockerfile.

With your dev container added and a basic understanding of what everything does, you can now make changes to configure it for your environment. In this example, you'll add properties to install npm when your codespace launches and make a list of ports inside the container available locally.

1. In the Explorer, select the devcontainer.json file from the tree to open it. You might have to expand the .devcontainer folder to see it.

2. Add the following lines to your devcontainer.json file after extensions:

   "postCreateCommand": "npm install",
   "forwardPorts": [4000],

   For more information on devcontainer.json properties, see the devcontainer.json reference in the Visual Studio Code docs.

3. Access the command palette (Shift + Command + P/ Ctrl + Shift + P), then start typing "rebuild". Select Codespaces: Rebuild Container.

   Rebuilding inside your codespace ensures your changes work as expected before you commit the changes to the repository. If something does result in a failure, you’ll be placed in a codespace with a recovery container that you can rebuild from to keep adjusting your container.

In the previous section, you used the postCreateCommand to installing a set of packages via npm. You can now use this to run our application with npm.

1. Run your start command in the terminal with npm start.

   

2. When your project starts, you should see a message in the bottom right corner with a prompt to connect to the port your project uses.

   

Once you've made changes to your codespace, either new code or configuration changes, you'll want to commit your changes. Committing changes to your repository ensures that anyone else who creates a codespace from this repository has the same configuration. This also means that any customization you do, such as adding Visual Studio Code extensions, will appear for all users.

For information, see "Using source control in your codespace."