Brad Curran

Moving from docker to nerdctl on macOS

TL;DR:

brew install lima
limactl start template://default
nerdctl.lima run --rm -it ubuntu:latest

Overview

If you've worked with docker on macOS, you've probably used Docker Desktop. It's an all-in-one solution for working with images and containers on macOS. While Docker Desktop is great to get started with containers, it hides a lot of the internals. Now that I'm doing a deep dive on docker, I thought it was time to upgrade.

Let's back up and explain how docker works. When you use docker on the command line, you're using the docker client. The client interacts with dockerd, the docker server. dockerd interacts with the linux container APIs.

macOS doesn't natively support container APIs, so how can we use containers in macOS? We have to run linux somehow. Typically, you'll run a linux virtual machine on macOS, then run the containers inside the linux VM.

We need to configure a linux VM on our mac. There's a bunch of ways to do this, but the method I've found easiest, while still maintaining low-level control is lima. It uses QEMU to run linux virtual machines on mac.

Setting up lima

Install brew if you haven't already. Install lima using brew:

brew install lima

This will add two commands, lima and limactl. limactl is used to manage VMs and lima is used to shell into the VMs.

Verify that the lima installed:

limactl ls
WARN[0000] No instance found. Run `limactl start` to create an instance.

We don't have any VMs installed, so let's install one:

limactl start template://default

? Creating an instance "default"  [Use arrows to move, type to filter]
> Proceed with the current configuration
  Open an editor to review or modify the current configuration
  Choose another example (docker, podman, archlinux, fedora, ...)
  Exit

Proceed with the current configuration. This will download and startup a VM configured to manage containers.

Note: You can see the example configurations available to you on GitHub or /usr/local/share/lima/examples/.

You should now be able to shell into the VM:

lima

Or if you want to type more characters (they both do the same thing):

limactl shell default

This should open a shell on the VM.

I have a VM, but I wanted to do container things

We still need a way to interact with the lima VM. The docker client interacts with dockerd over a unix socket. But lima uses containerd instead of dockerd. So we need to run an alternative docker client. Fortunately, lima comes with a client called nerdctl. The CLI is very close to the existing docker CLI, which makes migration really easy. 

lima nerdctl images

The above is SSHing into your lima VM, running nerdctl images, and printing the output. You can use the nerdctl.lima command as an alternative too:

nerdctl.lima images

I like to alias nerdctl to nerdctl.lima in my shell to make things a little easier:

# in my .zshrc
alias nerdctl='nerdctl.lima'

Now you can finally start using containers!

nerdctl run --rm -it ubuntu:latest
...
elapsed: 22.5s
root@d5d2eb94204a:/# echo 'hello world!'
hello world!

Now you can work with containers and have a lot more control over the system that runs the containers. Happy hacking!

References

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