Shared Volumes

Quick Overview of the Volumes Options

If option is marked Automatic, then you do not have to do anything for this option to be used.

If option is not Automatic, then you need to enable it manually on the global or project level to use. All non-automatic options are enabled by placing DOCKSAL_VOLUMES="<value from volumes column>" into the respective docksal.env file or using fin config set for the same, e.g., fin config set DOCKSAL_VOLUMES="NFS". Once you set a new volumes option, you must re-create cli container. The easiest way is fin project reset, but it will also remove all the data from db volume. If you want to retain it, remove cli container and start the project again to recreate it: fin p remove cli; fin p start

OS Docker Volumes Automatic Comments
Linux Native bind Yes Direct project files access, native FS speed.
macOS VirtualBox nfs Yes cli accesses project files from host via NFS.
Pros: pretty fast, only 10-15% slower than native filesystem.
Cons: does not support filesystem events (fsnotify).
macOS Docker for Mac bind Yes Files from host are shared with VM via osxfs, then cli accesses them directly.
Pros: supports filesystem events and is default for Docker for Mac.
Cons: pretty slow, 40-50% slower than native filesystem.
macOS Docker for Mac nfs No cli accesses project files from host via NFS.
Pros: much faster than bind option. NFS is only 10-15% slower than native filesystem.
Cons: does not support filesystem events (fsnotify).
Windows ANY bind Yes Files from host are shared with VM via SMB, then cli accesses them directly.
Pros: relatively fast, 20% overhead as compared to native FS.
Cons: does not support filesystem events (fsnotify).
ANY ANY unison No Files from host are shared with VM, but cli does not access them directly. Instead, cli filesystem is an independent volume, and files are synced from the VM to cli via an additional Unison container. Useful for huge projects where FS performance is a bottleneck.
Pros: maximum cli filesystem performance.
Cons: initial wait for files to sync into cli; additional Docksal disk space use; sync delay when you switch git branches; higher CPU usage during files sync; sometimes Unison might ‘break.’
ANY ANY none No none option is like unison, but without the auto-sync. Useful for huge projects where FS performance is a bottleneck, but when unison does not work for you.
Pros: maximum cli filesystem performance and no wait for the initial sync.
Cons: you have to copy files manually or checkout and edit files inside cli container only.

Full explanation on volumes in Docksal

Let’s go over volumes in Docker first.

In Docker, volumes are used primarily for persisting data generated by and used by Docker containers. Docker automatically creates and manages volumes, storing them in a special location within the host machine’s filesystem. There are also different volume plugins, which add support for various other data storage backends for volumes.

Mounting an existing folder from the host machine can also be done via volumes using bind mounts.

By default, Docksal uses the bind mount approach.

The VM layer used on macOS/Windows (through VirtualBox or Docker for Mac/Windows) adds some complexity to that, however that’s not something you normally have to worry about. Both Docksal and Docker for Mac/Windows handle that automatically.

From the perspective of a container, a local Linux path is mounted regardless of the underlying host OS. On Mac, the host filesystem is mounted with NFS, on Windows - using SMB.

Let’s take a look at an example.

The host machine is a macOS and the codebase root directory (the “Projects” folder) is /Users/username/Projects. This directory is mounted with the same path inside the VM: /Users/username/Projects. Any path within that directory is exactly the same on the host and inside the VM.

When a project stack is started, the project root directory (e.g., /Users/username/Projects/myproject) is bind mounted into /var/www inside the containers. A corresponding line in docksal.yml for this would be:

version: "2.1"

      - ${PROJECT_ROOT}:/var/www:rw

${PROJECT_ROOT} is automatically set to the project’s root directory on the host.

The whole mount chain looks like this (drop the last part for Linux hosts).

container ==bind mount==> Linux VM ==NFS/SMB mount==> Mac/Windows host   

Bind Volumes

Bind volumes mean native binding of files on host filesystem to Docker. But remember that on macOS and Windows “host filesystem” for Docker is actually a filesystem of a Virtual Machine it runs in. So while bind volumes can be used there it actually means that files from your real host has to be mapped into the VM first for this option to work. On macOS it means mapping via osxfs:cached, while on Windows via SMB.

Instead of using a host path every time we want to mount a volume, we can give the volume a name and refer to it by name:

version: "2.1"

      # Project root volume
      - project_root:/var/www:rw,nocopy
      # Shared ssh-agent socket
      - docksal_ssh_agent:/.ssh-agent:ro

    driver: local
      type: none
      device: ${PROJECT_ROOT}
      o: bind
    external: true

In the example above, project_root and docksal_ssh_agent are “named volumes.” The first one is a project level one, while the second one is a global volume and is used by all projects.

See stacks/volumes-bind.yml.

Defining volumes this way makes it much easier to override volume settings in one place (volumes section) vs multiple places in the yaml file. We can now swap bind mounting with something else. See below.

osxfs:cached Mode with Docker for Mac

As explained above for bind volumes option the files are actually mapped to the VM that Docker runs in via osxfs:cached. Docksal automatically enables the osxfs:cached mode on Docker for Mac.

See stacks/overrides-osxfs.yml.

NFS Volumes

With this option cli container will map files directly from your real host, rather than mapping them from the Virtual Machine that Docker runs in.

version: "2.1"

  cli_home:  # /home/docker volume in cli
  project_root:  # Project root volume (NFS)
    driver: local
      type: nfs
      device: :${PROJECT_ROOT}
      o: addr=${DOCKSAL_HOST_IP},vers=3,nolock,noacl,nocto,noatime,nodiratime,actimeo=1
  db_data:  # Database data volume (bind)
  docksal_ssh_agent:  # Shared ssh-agent volume
    external: true

See stacks/volumes-nfs.yml.

This is what the file sharing chain looks like with a NFS volume.

container:/var/www ==bind mount==> project_root ==> Linux:project_root ==NFS==> macOS:PROJECT_ROOT

As you can see, containers mount NFS via the host machine and not directly. This setup method only makes sense on macOS with Docker for Mac, for testing and performance comparison purposes.

Using NFS Volumes

  • Add DOCKSAL_VOLUMES=nfs either globally in $HOME/.docksal/docksal.env or in .docksal/docksal.env in a project
  • fin project reset

Unison Volumes

We can also do more advanced and pretty interesting solutions, like using Unison to synchronize files between the host and the project_root volume.

See stacks/volumes-unison.yml.

Unison volumes make the most sense for Docker for Mac users as an alternative to the (still slow) osxfs file sharing.

This is what the file sharing chain looks like with Unison over osxfs.

container:/var/www ==bind mount==> project_root <==unison daemon==> Linux:PROJECT_ROOT ==osxfs==> macOS:PROJECT_ROOT

project_root is a named volume, PROJECT_ROOT is a path on the host mounted into the same path in the VM via osxfs. unison daemon does a TWO WAY sync between PROJECT_ROOT and project_root.

Unlike NFS or SMB, osxfs supports inotify events, which makes it an ideal option for front-end developers relying on automatic compilation tools and in-browser live reloading. In the chain above, inotify events are not lost and are propagated all the way from the macOS host to the container.

The benefits of this setup:

  • Full native container file system performance (reads and writes)
  • ionitify event support
  • Low latency (~1s), two way file sync

The downsides:

  • Initial sync can take time, especially on large codebases
  • Higher disk space usage (double the size of the codebase)
  • Additional load from the unison daemon, but nothing compared to the load osxfs produces.

Using Unison Volumes

Unprecedented, native-like FS speed on macOS and Windows (Linux is already native). See docksal/unison for details

  • Install Docksal
  • Add DOCKSAL_VOLUMES=unison in .docksal/docksal.env in a project
  • fin project reset
  • Wait until initial sync finishes.

None Volumes

This method is similar to the Unison method, but without the actual sync happening at all.
Nothing is mounted from the host. An empty project_root volume is created and mounted inside containers.

This can be used to provision completely blank environments and have all work (code checkout, etc.) done inside cli.

Provides THE BEST file system performance. Combined with Cloud9, can provide a way of provisioning instant blank development environments with the best performance and consistency for Mac and Windows (Linux has the best performance naturally). The only added cost is having to stick with a web based IDE and terminal.

See stacks/volumes-none.yml.

When a project is created, there are a few volumes created for it. One of them is called <project_name>_project_root (where <project_name> is the machine name of your project). This volume is mapped to a specific location on the host. If you need to move the location of a project on the host system, the project stack will first need to be removed (run fin project rm inside the project), then you can move the project folder and start the project stack again.