progress on LXD post

content/posts/lxd-containers-for-human-beings.md

@@ -48,10 +48,10 @@ migrate as soon as there's an installable release.
   RAM, it's going to make do with 200 MBs of RAM and the kernel's <abbr
   title="Out Of Memory">OOM</abbr> 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.
+  treated as closed 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.
@@ -124,19 +124,43 @@ 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.
+VMs use virtualisation to achieve isolation. Containers use **namespaces** and
+**cgroups**, technologies pioneered in the Linux kernel. By now, though, there
+are [equivalents for Windows] and possibly other platforms.
 
-- **[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
+[equivalents for Windows]: https://learn.microsoft.com/en-us/virtualization/community/team-blog/2017/20170127-introducing-the-host-compute-service-hcs
+
+**[Linux namespaces]** partition kernel resources like process IDs, hostnames,
+user IDs, directory hierarchies, network access, etc. This prevents one
+collection of processes from seeing or gaining access to data regarding another
+collection of processes.
+
+**[Cgroups]** limit, track, and isolate the hardware resource use of a
+collection of processes. If you tell a cgroup that it's only allowed to spawn
+500 child processes and someone executes a fork bomb, the fork bomb will expand
+until it hits that limit. The kernel will prevent it from spawning further
+children and you'll have to resolve the issue the same way you would with VMs:
+delete and re-create it, restore from a good backup, etc. You can also limit CPU
+use, the number of CPU cores it can access, RAM, disk use, and so on.
 
 [Linux namespaces]: https://en.wikipedia.org/wiki/Linux_namespaces
 [Cgroups]: https://en.wikipedia.org/wiki/Cgroups
 
 ### Application containers
 
+The most well-known example of application container tech is probably
+[Docker.][docker] The goal here is to run a single application as minimally as
+possible inside each container. In the case of a single, statically-linked Go
+binary, a minimal Docker container might contain nothing more than the binary.
+If it's a Python application, you're more likely to use an [Alpine Linux image]
+and add your Python dependencies on top of that. If a database is required, that
+goes in a separate container. If you've got a web server to handle TLS
+termination and proxy your application, that's a third container. One cohesive
+system might require many Docker containers to function as intended.
+
+[docker]: https://docker.com/
+[Alpine Linux image]: https://hub.docker.com/_/alpine
+
 ```kroki {type=d2,d2theme=flagship-terrastruct,d2sketch=true}
 Host kernel.Container runtime.c1: Container
 Host kernel.Container runtime.c2: Container
@@ -149,6 +173,21 @@ Host kernel.Container runtime.c3.Full OS.Many apps
 
 ### System containers
 
+One of the most well-known examples of system container tech is the subject of
+this post: LXD! Rather than containing a single application or a very small set
+of them, system containers are designed to house entire operating systems, like
+[Debian] or [Rocky Linux,][rocky] along with everything required for your
+application. Using our examples from above, a single statically-linked Go binary
+might run in a full Debian container, just like the Python application might.
+The database and webserver might go in _that same_ container.
+
+[Debian]: https://www.debian.org/
+[rocky]: https://rockylinux.org/
+
+You treat each container more like you would a VM, but you get the performance
+benefit of _not_ virtualising everything. Containers are _much_ lighter than any
+virtual machine.
+
 ```kroki {type=d2,d2theme=flagship-terrastruct,d2sketch=true}
 hk: Host kernel
 hk.c1: Container
@@ -162,29 +201,42 @@ hk.c2.os2.app2: Many apps
 hk.c3.os3.app3: Many apps
 ```
 
-## When to use VMs
+## When to use which
 
-- 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 type="warn" >}}
+**Warning:** this is my personal opinion. Please evaluate each technology and
+determine for yourself whether it's a suitable fit for your environment.
 {{< /adm >}}
 
-### When you use application containers
+As far as I'm aware, VMs are your only option when you want to work with
+esoteric hardware or hardware you don't physically have on-hand. It's also your
+only option when you want to work with foreign operating systems: running Linux
+on Windows, Windows on Linux, or OpenBSD on a Mac all require virtualisation.
+Another reason to stick with VMs is for compliance purposes. Containers are
+still very new and some regulatory bodies require virtualisation because it's a
+decades-old and battle-tested isolation technique.
 
-- 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 😉)
+{{< adm type="note" >}}
+See Drew DeVault's blog post [_In praise of qemu_][qemu] for a great use of VMs
 
-### System containers
+[qemu]: https://drewdevault.com/2022/09/02/2022-09-02-In-praise-of-qemu.html
+{{< /adm >}}
 
-- Anything not listed above 👍
+Application containers are particularly popular for [microservices] and
+[reproducible builds,][repb] though I personally think [NixOS] is a better fit
+for the latter. App containers are also your only option if you want to use
+cloud platforms with extreme scaling capabilities like Google Cloud's App Engine
+standard environment or AWS's Fargate.
+
+[microservices]: https://en.wikipedia.org/wiki/Microservices
+[repb]: https://en.wikipedia.org/wiki/Reproducible_builds
+[NixOS]: https://nixos.org/
+
+  - 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