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Docker

Overview​

Docker is useful because it allows you to both package and run software with all its dependencies and configuration in isolation. It also allows you (in theory) to have the same environment in development as in CI and production.

Installation​

You should install via homebrew

brew cask install docker

Configuration of Shared Folders​

Anecdata suggests that removing some of the default shared folders can decrease CPU usage. Usually you only need to share volumes under your home directory. Open the docker for mac preferences, then select "File Sharing" and then remove /Volumes and /private. You may also find improvements removing /Users and replacing it with /Users/YOUR_USERNAME_GOES_HERE.

Configuration of Storage Driver​

If you've been running Docker for Mac for some time, make sure you are using the overlay2 storage driver.

$ docker info |grep Storage
Storage Driver: overlay2

If you don't see overlay2, upgrading to the latest version will add that support, but you would need to recreate all of your docker data to utilize it. The Reset bomb should do it.

Configuration of Disk Image​

If you've been running Docker for Mac for some time, make sure you are using the raw disk image format and not qcow2. Open Docker for Mac preferences and select Disk. Make sure the image ends with Docker.raw.

Configuration of Resources​

Because docker uses a Virtual Machine under the hood on macOS, you can choose the maximum number of resources it is allowed to use. In the preferences under Advanced, you can select how many CPUs to assign, how much memory to assign, and how much swap to give the VM.

See also Understanding memory usage in Docker Desktop on Mac by the docker developers.

Volume Mount Performance​

Synchronizing the data between the host (your Mac) and the container can be resource intensive and/or slow. Read about the performance tuning options to see if they might apply to the conditions in your project.

Inspecting the Docker Virtual Machine​

If you are having performance problems or are just curious, you can run commands inside the Virtual Machine with

docker run --rm=true -it --privileged --pid=host \
    justincormack/nsenter1 /usr/bin/top

Inspecting Container Resources​

To get a top like report of what your containers are doing

docker stats

Cleaning Up​

To see where all your disk space is going:

docker system df

To remove stopped containers, dangling images, the build cache and unused networks:

docker system prune

See the docker system prune documentation for more options like pruning volumes

Docker Configuration​

You can configure all sorts of defaults in the docker config.json.

Keybindings​

If you dislike the default detach keybindings of CTRL-p CTRL-q, you can override it in config.json with something like:

{
  "detachKeys": "ctrl-@,ctrl-["
}

Credentials Store​

You can store docker credentials in an external credentials store.

On macOS, the keychain will be used by default, but if you need/want to store shared credentials, pass can be used.

Additional Resources​

If you would like to dig deeper into how Docker works, how it isolates code from the host machine, and related ramifications a good place to start are the articles listed below.