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Sail can be thought of as a wrapper around the Docker toolchain, focused on managing development environments.

It stores most of it’s state in the Docker daemon in the form of metadata and labels.


Sail tries to encourage a workflow of explicitly describing your development environment in a way that’s easy to share and iterate on.

If you want to make a change to the environment, you should modify your hat or the project’s Dockerfile.

Project Defined Environment

Projects can define their own environment by specifying a .sail/Dockerfile file. If a .sail/Dockerfile is not present in a repository, the codercom/ubuntu-dev image will be used as the base environment.

When specifying a custom project environment, the dev container must have be an ancestor of codercom/ubuntu-dev in order to have the proper dependencies setup.

When building the project’s image, the build will be rooted in the project’s root, essentially calling this docker build command:

 docker build -f $project_root/<org>/<repo>/.sail/Dockerfile $project_root/<org>/<repo>

Container Permissions

The current user on the host is mapped to the user named user within the development environment. That means files permissioned to user within the container, will appear to have the same set of permissions for your user on the host.

Sail uses user and not root within the container because:

  • A lot of tools will complain about being root.
  • Most developers are used to being non-root and the sudo workflow.

Container Naming

Containers are named <org>_<project> in Docker, but <org>/project in Sail.


To keep workflow as close to local development as possible, sail uses docker host networking when possible. That means if your webserver within Sail binds to :8080, it will be accessible from in your browser.

Docker for Mac doesn’t support host networking, so this won’t work when running Sail on a Mac host. A workaround is planned for a future release of Sail.

Dockerfile Best Practices

Dockerfile best practices for a reference on how to properly structure and write your project and hat Dockerfiles.