Shared Volumes

Quick Overview

OS VM DOCKSAL_VOLUMES FS Speed FS Events Comments
Linux - bind (default) 100% Yes Direct host files access, maximum filesystem speed.
macOS VirtualBox nfs (default) 80% Uses nfs for best overall for macOS. Stable, lightweight.
macOS Docker Desktop nfs (default) 80% Uses nfs for best overall for macOS. Stable, lightweight.
macOS Docker Desktop bind 60% Yes Uses osxfs. Can cause higher CPU usage.
macOS Docker Desktop unison 100% Yes Uses osxfs. Can be unstable, especially on large codebases.
Windows ANY bind (default) 50% Uses SMB - the only option for Windows.
ANY ANY none 100% Work on the codebase has to be done inside the cli container.

Project Volumes

If you are familiar with Docker Compose, then you must have attached files or dirs like this:

  cli:
    volumes:
      - /Users/alex/mysite:/var/www:rw

That is a called a bind mount - mounting a file/folder directly into a container. However, to support various OS in Docksal, we cannot always rely on bind mounts.

Docksal defines several named Docker volumes per project for you:

  • project_root stores your project files (see warnings below about use cases for this volume)
  • cli_home stores home folder of your cli container independently of the cli container
  • db_data stores your database data independently of the db container
  • docksal_ssh_agent stores SSH keys shared with all project stacks

Docksal makes these volumes to function transparently across different operating systems, but their actual definitions vary depending on the DOCKSAL_VOLUMES option.

project_root volume is mapped to a specific location on the host. If you need to move the location of a project on the computer, remove the project stack first with fin project rm, then you can move the project folder and start the project stack again.

When customizing docksal.yml, make sure to include the cached option anywhere the project_root volume is attached to a service. Mixing cached and non-cached mounts for the same volume in your project stack will lead to issues and errors with Docker Desktop on macOS. See docksal/docksal#678 for more details.

DOCKSAL_VOLUMES

DOCKSAL_VOLUMES value changes the mount type of the project volumes mentioned above and also affects fin behavior.

bind

With this option, containers access files via a bind mount, which basically means direct access.

While Docker can access files directly on Linux, on macOS and Windows it works inside the VM (VirtualBox, xhyve/Hyper-V with Docker Desktop), which means that Docker cannot directly access files from host. Those files have to be made available inside the VM first, and this is achieved in different ways on different operating systems and VMs.

On macOS with VirtualBox, files are made available from host to Docker by mounting the folder defined in DOCKSAL_NFS_PATH into the VM via NFS protocol.

             NFS mount                     bind mount
macOS Host ==============> VirtualBox VM =============> Container

On macOS with Docker Desktop, it is Docker Desktop itself that mounts folders defined in Docker Desktop UI via osxfs file system.

             osxfs mount                    bind mount
macOS Host ==============> Docker Desktop ==============> Container

On Windows with VirtualBox, Docksal mounts all physical drives into the VM via SMB protocol.

               SMB mount                    bind mount
Windows Host =============> VirtualBox VM ==============> Container

On Windows with Docker Desktop, it is Docker Desktop itself that mounts only configured Windows drives via SMB.

               SMB mount                     bind mount
Windows Host =============> Docker Desktop ==============> Container

To see how your project’s Docker volumes are defined with DOCKSAL_VOLUMES=bind, see stacks/volumes-bind.yml.

In most cases, you do not need to set the DOCKSAL_VOLUES=bind option. It is set for you automatically. The only exception is when you need fsnotify events on macOS with Docker Desktop, but don’t want to use the unison option.

nfs

This option is macOS specific and is used by default with both VirtualBox and Docker Desktop.
Docker mounts the project_root volume from the host over NFS, then project containers mount this volume.

            volume mounted via NFS
macOS Host ========================> Container

NFS generally works faster than osxfs. The downside is that NFS does not support fsnotify events.

To see how your project’s Docker volumes are defined with DOCKSAL_VOLUMES=nfs, see stacks/volumes-nfs.yml.

unison

This option only makes sense with Docker Desktop on macOS.

A unison container is added to the project stack with two volumes attached to it:

  • a bind mount of the osxfs mount from the host - slow, but supports fsnotify
  • a project_root named volume - native filesystem performance for containers (empty initially)
            osxfs                   bind                      volume
macOS Host =======> Docker Desktop ======> unison container <======== project_root

The Unison daemon is responsible for syncing files between the two volumes.

unison container   -------> osxfs mount from macOS host (w/ fsnotify)
  two-way sync     \
  between volumes   \
                      ---> project_root volume

Project containers do not access files on the host directly, so there is no performance penalty of using osxfs or NFS for containers.

The benefits of this setup:

  • Native container file system performance for codebase reads and writes
  • Support for filesystem watchers

The downsides:

  • Initial sync can take time, especially on large codebases
  • Higher disk space usage (double the size of the codebase)
  • Additional CPU load from the Unison daemon

Using “unison” Volumes

fin config set DOCKSAL_VOLUMES=unison
fin project reset

Wait until the initial unison sync finishes.

Once you set a new DOCKSAL_VOLUMES option, you must recreate the cli container. The easiest way is fin project reset, but it will also remove all data from the db volume. If you want to retain it, remove only the cli container, and start the project again: fin project remove cli; fin project start

To see how your project’s Docker volumes are defined with DOCKSAL_VOLUMES=unison see stacks/volumes-unison.yml.

none

Advanced option. With this option, host files are made accessible to the VM like in a bind mount, but after that containers do not access them directly via bind, nor files are copied over. You would have to copy files into container and back manually.

Combined with VSCode IDE, this option can provide a way of provisioning instant blank development environments with the best performance and consistency for Mac and Windows. The only added cost is having to stick with a browser-based IDE and terminal for developer UX.

See stacks/volumes-none.yml for details on Docker volumes definition with this option.

Using “none” Volumes

fin config set DOCKSAL_VOLUMES=none
fin project reset

Use fin bash to log into bash and checkout files into /var/www with git. Or use fin docker cp to copy files into the cli container.