--- title: "LXD: Containers for Human Beings" subtitle: "Docker's great and all, but I prefer the workflow of interacting with VMs" date: 2023-08-11T16:30:00-04:00 categories: - Technology tags: - Sysadmin - Containers - VMs - Docker - LXD draft: true rss_only: false cover: ./cover.png --- This is a blog post version of a talk I presented at both Ubuntu Summit 2022 and SouthEast LinuxFest 2023. The first was not recorded, but the second was and is on [SELF's PeerTube instance.][selfpeertube] I apologise for the terrible audio, but there's unfortunately nothing I can do about that. If you're already intimately familiar with the core concepts of VMs or containers, I would suggest skipping those respective sections. If you're vaguely familiar with either, I would recommend reading them because I do go a little bit in-depth. [selfpeertube]: https://peertube.linuxrocks.online/w/hjiTPHVwGz4hy9n3cUL1mq?start=1m {{< adm type="warn" >}} **Note:** Canonical has decided to [pull LXD out][lxd] from under the Linux Containers entity and instead continue development under the Canonical brand. The majority of the LXD creators and developers have congregated around a fork called [Incus.][inc] I'll be keeping a close eye on the project and intend to migrate as soon as there's an installable release. [lxd]: https://linuxcontainers.org/lxd/ [inc]: https://linuxcontainers.org/incus/ {{< /adm >}} ## The benefits of VMs and containers - **Isolation:** you don't want to allow an attacker to infiltrate your email server through your web application; the two should be completely separate from each other and VMs/containers provide strong isolation guarantees. - **Flexibility:** VMs and containers only use the resources they've been given. If you tell the VM it has 200 MBs of RAM, it's going to make do with 200 MBs of RAM and the kernel's OOM killer is going to have a fun time 🤠 - **Portability:** once set up and configured, VMs and containers can mostly be treated as black boxes; as long as the surrounding environment of the new host is similar to the previous in terms of communication (proxies, web servers, etc.), they can just be picked up and dropped between various hosts as necessary. - **Density:** applications are usually much lighter than the systems they're running on, so it makes sense to run many applications on one system. VMs and containers facilitate that without sacrificing security. - **Cleanliness:** VMs and containers are applications in black boxes. When you're done with the box, you can just throw it away and most everything related to the application is gone. ## Virtual machines As the name suggests, Virtual Machines are all virtual; a hypervisor creates virtual disks for storage, virtual CPUs, virtual NICs, virtual RAM, etc. On top of the virtualised hardware, you have your kernel. This is what facilitates communication between the operating system and the (virtual) hardware. Above that is the operating system and all your applications. At this point, the stack is quite large; VMs aren't exactly lightweight, and this impacts how densely you can pack the host. I mentioned a "hypervisor" a minute ago. I've explained what hypervisors in general do, but there are actually two different kinds of hypervisor. They're creatively named **Type 1** and **Type 2**. ### Type 1 hypervisors These run directly in the host kernel without an intermediary OS. A good example would be [KVM,][kvm] a **VM** hypervisor than runs in the **K**ernel. Type 1 hypervisors can communicate directly with the host's hardware to allocate RAM, issue instructions to the CPU, etc. [debian]: https://debian.org [kvm]: https://www.linux-kvm.org [vb]: https://www.virtualbox.org/ ```kroki {type=d2,d2theme=flagship-terrastruct,d2sketch=true} hk: Host kernel hk.h: Type 1 hypervisor hk.h.k1: Guest kernel hk.h.k2: Guest kernel hk.h.k3: Guest kernel hk.h.k1.os1: Guest OS hk.h.k2.os2: Guest OS hk.h.k3.os3: Guest OS hk.h.k1.os1.app1: Many apps hk.h.k2.os2.app2: Many apps hk.h.k3.os3.app3: Many apps ``` ### Type 2 hypervisors These run in userspace as an application, like [VirtualBox.][vb] Type 2 hypervisors have to first go through the operating system, adding an additional layer to the stack. ```kroki {type=d2,d2theme=flagship-terrastruct,d2sketch=true} hk: Host kernel hk.os: Host OS hk.os.h: Type 2 hypervisor hk.os.h.k1: Guest kernel hk.os.h.k2: Guest kernel hk.os.h.k3: Guest kernel hk.os.h.k1.os1: Guest OS hk.os.h.k2.os2: Guest OS hk.os.h.k3.os3: Guest OS hk.os.h.k1.os1.app1: Many apps hk.os.h.k2.os2.app2: Many apps hk.os.h.k3.os3.app3: Many apps ``` ## Containers As most people know them right now, containers are exclusive to Linux.[^1] This is because they use namespaces and cgroups to achieve isolation. - **[Linux namespaces]** partition kernel resources like process IDs, hostnames, user IDs, directory hierarchies, network access, etc. - **[Cgroups]** limit, track, and isolate the hardware resource use of a set of processes [Linux namespaces]: https://en.wikipedia.org/wiki/Linux_namespaces [Cgroups]: https://en.wikipedia.org/wiki/Cgroups ### Application containers ```kroki {type=d2,d2theme=flagship-terrastruct,d2sketch=true} Host kernel.Container runtime.c1: Container Host kernel.Container runtime.c2: Container Host kernel.Container runtime.c3: Container Host kernel.Container runtime.c1.One app Host kernel.Container runtime.c2.Few apps Host kernel.Container runtime.c3.Full OS.Many apps ``` ### System containers ```kroki {type=d2,d2theme=flagship-terrastruct,d2sketch=true} hk: Host kernel hk.c1: Container hk.c2: Container hk.c3: Container hk.c1.os1: Full OS hk.c2.os2: Full OS hk.c3.os3: Full OS hk.c1.os1.app1: Many apps hk.c2.os2.app2: Many apps hk.c3.os3.app3: Many apps ``` ## When to use VMs - Virtualising esoteric hardware - Virtualising non-Linux operating systems (Windows, macOS) - Completely isolating processes from one another with a decades-old, battle-tested technique {{< adm type="note" >}} See Drew DeVault's blog post [_In praise of qemu_](https://earl.run/rmBs) for a great use of VMs {{< /adm >}} ### When you use application containers - Microservices - Extremely reproducible builds - (NixOS.org would likely be a better fit though) - Dead-set on using cloud platforms with extreme scaling capabilities (AWS, GCP, etc.) - When the app you want to run is _only_ distributed as a Docker container and the maintainers adamantly refuse to support any other deployment method - (Docker does run in LXD 😉) ### System containers - Anything not listed above 👍 ## Crash course to LXD ### Installation {{< adm type="note" >}} **Note:** the instructions below say to install LXD using [Snap.][snap] I personally dislike Snap, but LXD is a Canonical product and they're doing their best to prmote it as much as possible. One of the first things the Incus project did was [rip out Snap support,][rsnap] so it will eventually be installable as a proper native package. [snap]: https://en.wikipedia.org/wiki/Snap_(software) [rsnap]: https://github.com/lxc/incus/compare/9579f65cd0f215ecd847e8c1cea2ebe96c56be4a...3f64077a80e028bb92b491d42037124e9734d4c7 {{< /adm >}} 1. Install snap following [Canonical's tutorial](https://earl.run/ZvUK) - LXD is natively packaged for Arch and Alpine, but configuration can be a massive headache. 2. `sudo snap install lxd` 3. `lxd init` 4. `lxc image copy images:debian/11 local: --alias deb-11` 5. `lxc launch deb-11 container-name` 6. `lxc shell container-name` ### Usage {install my URL shortener} [^1]: Docker containers on Windows and macOS actually run in a Linux VM.