Devcontainers

Devcontainers, short for development containers, are containerized development environments defined within a project's repository. They provide isolated, reproducible toolchains and dependencies so that all contributors work with the same software stack, regardless of their host operating system. A devcontainer is typically defined in a .devcontainer folder at the repository root, and includes a devcontainer.json file along with either a Dockerfile or a reference to an image.

Key elements of a devcontainer include a build specification and workspace configuration. The build can reference a Dockerfile or an image, and may specify a build context, environment variables, and run arguments. The devcontainer.json file lists extensions to install in the editor, editor settings to apply inside the container, ports to forward, commands to run after creation, and how the workspace is mounted. An optional docker-compose.yml can be used for multi-service setups, allowing services and dependencies to be defined together.

Usage typically involves a code editor such as Visual Studio Code with the Remote - Containers extension, or through GitHub Codespaces. The editor connects to the container, builds the image as defined, starts the container, and exposes the project workspace inside the editor. This enables features like code completion, debugging, and terminal access to operate against the exact same environment used during development and testing.

Benefits of devcontainers include reproducibility, isolation from host configurations, faster onboarding, and closer parity between development, testing, and CI environments. Limitations to consider include the need for a container runtime on the host, potential performance overhead, and the complexity of troubleshooting inside containers. Devcontainers are commonly used with Docker or Podman, and are integral to workflows in VS Code Remote - Containers and GitHub Codespaces.