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Dev Containers

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Dev containers define your development environment as code using a devcontainer.json file. Coder's Dev Containers integration uses the @devcontainers/cli and Docker to seamlessly build and run these containers, with management in your dashboard.

This guide covers the Dev Containers integration. For workspaces without Docker, administrators can configure Envbuilder instead, which builds the workspace image itself from your dev container configuration.

Two dev containers running as sub-agents in a Coder workspaceDev containers appear as sub-agents with their own apps, SSH access, and port forwarding

Prerequisites

  • Coder version 2.24.0 or later
  • Docker available inside your workspace
  • The @devcontainers/cli installed in your workspace

Dev Containers integration is enabled by default. Your workspace needs Docker (via Docker-in-Docker or a mounted socket) and the devcontainers CLI. Most templates with Dev Containers support include both. See Configure a template for dev containers for setup details.

Features

  • Automatic dev container detection from repositories
  • Seamless container startup during workspace initialization
  • Change detection with outdated status indicator
  • On-demand container rebuild via dashboard button
  • Template-defined apps, scripts, and environment variables via Terraform (see limitations)
  • Integrated IDE experience with VS Code
  • Direct SSH access to containers
  • Automatic port detection

Get started

Add a devcontainer.json

Add a devcontainer.json file to your repository. This file defines your development environment. You can place it in:

  • .devcontainer/devcontainer.json (recommended)
  • .devcontainer.json (root of repository)
  • .devcontainer/<folder>/devcontainer.json (for multiple configurations)

The third option allows monorepos to define multiple dev container configurations in separate sub-folders. See the Dev Container specification for details.

Here's a minimal example:

{ "name": "My Dev Container", "image": "mcr.microsoft.com/devcontainers/base:ubuntu" }

For more configuration options, see the Dev Container specification.

Start your dev container

Coder automatically discovers dev container configurations in your repositories and displays them in your workspace dashboard. From there, you can start a dev container with a single click.

Discovered dev containers with Start buttonsCoder detects dev container configurations and displays them with a Start button

If your template administrator has configured automatic startup (via the coder_devcontainer Terraform resource or autostart settings), your dev container will build and start automatically when the workspace starts.

Connect to your dev container

Once running, your dev container appears as a sub-agent in your workspace dashboard. You can connect via:

  • Web terminal in the Coder dashboard
  • SSH using coder ssh <workspace>.<agent>
  • VS Code using the "Open in VS Code Desktop" button

See Working with dev containers for detailed connection instructions.

How it works

The Dev Containers integration uses the devcontainer command from @devcontainers/cli to manage containers within your Coder workspace.

When a workspace with Dev Containers integration starts:

  1. If the template defines coder_app, coder_script, or coder_env resources attached to the dev container, a sub-agent is pre-created with these resources.
  2. The workspace initializes the Docker environment.
  3. The integration detects repositories with dev container configurations.
  4. Detected dev containers appear in the Coder dashboard.
  5. If auto-start is configured (via coder_devcontainer or autostart settings), the integration builds and starts the dev container automatically.
  6. Coder creates a sub-agent (or updates the pre-created one) for the running container, enabling direct access.

Without auto-start, users can manually start discovered dev containers from the dashboard.

Agent naming

Each dev container gets its own agent name, derived from the workspace folder path. For example, a dev container with workspace folder /home/coder/my-app will have an agent named my-app.

Agent names are sanitized to contain only lowercase alphanumeric characters and hyphens. You can also set a custom agent name in your devcontainer.json.

Limitations

  • Linux only: Dev Containers are currently not supported in Windows or macOS workspaces
  • Changes to devcontainer.json require manual rebuild using the dashboard button
  • The forwardPorts property in devcontainer.json with host:port syntax (for example, "db:5432") for Docker Compose sidecar containers is not yet supported. For single-container dev containers, use coder port-forward to access ports directly on the sub-agent.
  • Some advanced dev container features may have limited support

Next steps