• 원본, Kubecon EU 2022
• Slide
• Slide 출처

Why run containers on macOS?

• 2022 is The Year of the Linux Desktop
• But ordinary developers still need macOS (or Windows)
• Almost solely for the dev & test environment
• Not the best fit for running a production server

Existing methods

• Docker Desktop for Mac has been the popular solution

• Supports automatic host filesystem sharing
• Supports automatic port forwarding

• But proprietary

• Just install Docker and Kubernetes inside a Linux VM? Maybe via minikube?:
  • VMWare Fusion and Parallels are proprietary
  • VirtualBox is FLOSS but won’t support M1
  • QEMU is FLOSS and supports M1, but still:
    • Not easy to access the host FS from the containers
    • Not easy to access the container ports from the host

Our solution: Lima

• Similar to WSL2 but for macOS hosts

• Automatic host filesystem sharing
• Automatic port forwarding
• Built-in integration for containerd

Lima = LInux MAchine

• Originally designed as “containerd machine” to mimic Docker Machine
• The scope was extended immediately to cover other use cases too
• Still focuses on containerd and k3s

continaerd with Lima

• continared: the de facto standard container runtime:
  • CNCF Graudated project
  • Not just made for Kubernetes
  • Provides the docker-compatible CLI too: nerdctl
  • With a lot of cutting-edge features:
    • Lazy-pulling, IPFS, OCIcryupt, Faster rootless…
• Lima provides built-in support for containerd
• Even supports running Intel(AMD64) containers on M1(ARM64) and vice versa, using tonistiigi/binfmt

k3s with Lima

• k3s: Lightweight Kubernetes:
  • CNCF Sandbox project
  • Adopts containerd as the CRI runtime
  • Works with Lima too

Extra: Docker with Lima

• The original design was only to support containerd, but the scope is now expanded to support Docker Engine too

Extra: Podman with Lima

How it works: Hypervisor

• Vanilla QEMU
• Supports both Intel and ARM
• Even supports Intel-on-ARM and ARM-on-Intel (slow though)
• FAQ: why not use Apple’s Virtualization.framework?:
  • Proprietary
  • Limited functionalities

How it works: Filesystem sharing

• Lima < 1.0 : reverse SSHFS:
  • macOS works as an SSH client but as an SFTP server
  • Linux works an SSH server but as an SFTP client
• Lima >= 1.0 : virtio-9p-pci, aka virtfs( not virtio-fs):
  • Less weirdness
  • Lima 1.0 is probably available by the time of KubeCon
• FAQ: why not use virtio-fs (faster than virtfs) ?:
  • QEMU still doesn’t implement virtio-fs for macOS hosts
  • Apple’s Virtualization.framework implements virtio-fs, but it is proprietary and lacks other functionalities

How its works: Port forwarding

• THe guest is accessible as localhost from the host
• Watch guest events, and run ssh -L to let SSH forward TCP ports
• Event sources:
  • /proc/net/{tcp,tcp6}: For non-CNI ports
  • iptables, AUDIT_NETFILTER_CFG : For CNI ports

Enterprise DNS Requirements

• Use nameservers from VPN connections
• Support for split-DNS
• Other QEMU DNS limitations:
  • Picks single random nameserver from /etc/resolv.conf
  • Cannot support mDNS
  • Doesn’t load /etc/hosts from the host

How it works: Host Resolver

• 여긴 그림이 있는데, 그림은 글 상단의 Slide Page 19 를 참고하면 된다.
• 대충 이해한대로 설명을 써보자면,:
  • Lima VM 은 QEMU 내부에서 실행되며, QEMU Internal Network 에 Virtual Network 로 붙어있다.
  • QEMU 내부에 존재하며, Host 와 연결을 해주는 HostGateWay로 Resolver를 요청한다.
  • HostGateway는 Host 위에서 동작하는 Lima Host Agent에 있는 Host Resolver와 DNS over UDP&TCP 로 통신한다.
  • 즉, 기존에 QEMU 내에 구현되어있던 DNS가 /etc/resolv.conf 에서 무작위로 선택하는 방식에서, macOS resolver를 최종적으로 호출하는 구조를 형성하여 /etc/resolv.conf, /etc/hosts, mdnsResponder, VPN 등에서 Domain Name을 가져오는게 가능해졌다.
• 영상에서 굉장히 설명을 깔끔하게 잘하고 있으니 영상을 설명을 들으면 좋다.

How it works: Proxy Settings

1. Network settings
2. lima.yaml
3. Environment variable

• 이것만 적어두면 조금 이해가 어려운데, Host Netowrk를 설정하고, lima.yaml 에 환경변수로 https_proxy,http_proxy를 127.0.0.1 에서 192.168.5.2 로 교체, 나머지 환경변수들을 설정해둔뒤 lima를 시작하면 된다.
• 궁금점 : 192.168.5.2 는 고정인건가?

Port Forwarding Limitations

• Port forwarding is delayed up to 3s due to polling
• Port may already be in use on the host
• Guest IP != Host IP breaks external IP for k8s services
• UDP is not supported by ssh port forwarding

How it works: vde_vmnet

• 이거 글로만 적으려니 어렵다. Slide 22 쪽을 참고하자. 그림은 그렇게 어렵지 않다.

Lima community after one year

• 45 contributors
• 400 merged pull requests
• 26 releases
• 8k stars on Github

Third party FOSS projects

• Lima-GUI
• Colima
• Rancher Desktop

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개인생각

• UDP 가 안된다는건 이거 안들었으면 몰랐을것 같다. Network를 이런식으로 구성해놨는지 몰랐다.
• lima 를 굉장히 자주 사용하고 있는데, 쓰면서 큰 장애를 못느꼇는데 생각보다 안되는게 좀 있었다는게 신기하다.
• hosts 파일이라던가 몇몇 기능을 지원하기 위해서 lima agent 를 띄우는 방식은 참신하다. 하지만 근본적인 해결책이라고 보이지는 않는다. QEMU 는 보안상, 또는 기능상의 이유로 막아두었을텐데 왜 그런지 좀 알았으면 이해가 더 좋았을 것같다.
• filesystem layer에 대해서 고민을 많이한게 보인다.