Currently the idea with k8s is that you just destroy anything that has broken state and rebuild it somewhere else. While this is the easiest solution to the problem, I think that containers should not always be treated like disposable objects.
I think in many ways, Solaris Zones (and FreeBSD Jails to a lesser extent) did this right. Every administrative command in Solaris is zone-aware and you can manage your zones like you manage your host. On Linux, containers are completely opaque root filesystems which contain who-knows-what and are completely unmanagable or introspectable by the host. Everyone is cargo-culting and creating hacks around this fundamentally opaque system to try to make it less opaque (or just giving up and making it easy to purge them).
I'm working on some improvements to the OCI image-spec that _might_ help with introspection of images[1], but runtime introspection is going to be quite hard (needs runtime agreement).
I get that it's no longer sexy to work on container runtimes, now that everyone is losing their mind over orchestrators (and I imagine soon they'll be losing their mind over the next big thing). But I think that improving these fundamental blocks is pretty interesting and might result in better systems.
you mean, as in "VM"? :)
For instance in your post I didn't really get your point because at one time you seem to favor containers as a single entity from the perspective of the OS so they can be easily managed. This is what I understand you called "transparent to the OS". The is opposed to the container root fs that you call "opaque", supposedly because it cannot be easily mounted from the host OS etc.
As the implementor of container runtimes you know that there's not a container entity but an agglomeration of isolation techniques such as namespaces, cgroups etc. including some kind of overlay fs that make up an actual container. For me that's not very transparent. VMs on the other hand are in that respect – in a similar way Solaris zones and Jails are, as they are actual entities that can be seen and managed on the host OS.
> The is opposed to the container root fs that you call "opaque", supposedly because it cannot be easily mounted from the host OS etc.
Well, you can mount it and you can manually funge with it using 'nsenter' but that's not really ideal. Why (from the perspective of a user) can't you run a package upgrade across your containers? Why can't you get the free memory across all containers? Free disk space? And so on. This information is _available_ but it's not cohesive for _users_.
> VMs on the other hand are in that respect – in a similar way Solaris zones and Jails are
I agree that Solaris Zones and FreeBSD Jails are transparent (in fact that level of tooling transparency is what I wish we had on Linux). I don't agree that VMs are transparent in the same way -- they are an opaque DRAM blob from the perspective of the host kernel. You can dtrace zones/jails, you cannot dtrace a VM (and get meaningful results about what the guest kernel is doing) AFAIK.
It makes it difficult to reason about containers, as well. For instance do you see confinement technologies such as AppArmor or SELinux belonging to the container or are they slapped on top of containers? Where do you draw the boundary? And does it make sense to talk about "containers" when it's such a vague concept. Also, there are now "VM containers" such as Kata.
Well at some point we have to be able to talk about the widely-used and glued-together namespaces+cgroups+... concept. "Containers" is a perfectly fine thing to discuss (especially since the history of namespaces was definitely based in more "fully fledged" container technologies like Xen).
> Also, there are now "VM containers" such as Kata.
... which are just VMs that can interact with container tools. I'm pretty sure that most people would not call these "containers" from an OS point of view because they do not share any of the primary properties that containers (or Jails/Zones) have -- the host kernel actually knows what the container processes are doing.
My biggest issue with the current state is that the common tools (e.g. Docker, k8s) are pretty terrible. Docker overcomplicates a great many things, which is one reason for the many bugs. And k8s ... well, let's not even go there.
I don't think much more is needed than just `run-container /usr/containers/cool-container` and presto, a container with the files in that directory. No need for buggy/slow platform-dependent FS abstraction layers that change every year because they never quite work right in a bazillion edge cases. This is how e.g. FreeBSD jails work.
This won't prevent implementing tools like `docker pull`; at it simplest it could be `curl ... | tar xf - -C /usr/containers/cool-container`. Running multiple containers based of a single image? `cp -r`.
Maybe I'm just an old Unix guy, but I think that composition from generic tools is a much better approach for a lot of this stuff. It's easier, less platform-dependent, has less code (meaning less bugs), etc.
I don't think it has to be; I mean, the current Linux/Docker situation is kind of that, but that's just a single implementation.
> most containers are bundles of software (multiple binaries)
Yeah, exactly. Containers aren't just about security, also convenience. Something like "docker pull someimage" can be a handy cross-platform way to run stuff.
I think "docker pull" is the reason for Docker's popularity. You can build a self-contained container containing Ruby, all your Ruby on Rails stuff and JS stuff, and whatnot, and then send that to any server and just "docker run" it. Getting some of this dynamic stuff to run can be tricky and error-prone: need to get the correct Ruby version, Rails version, muck about with bundle, etc.
Want to add a new app-server or migrate to somewhere else? Need to spend a day setting everything up again and hope you didn't make a mistake that will bite you later :-(
A self-contained container is a lot easier, even with good OS package management or automation tools like Puppet.
Many people also use Docker as "Vagrant" (e.g. to run dev versions or tests and whatnot). Again, "docker pull" is convenient here, especially when there are certain dependencies/requirements, or for running testing against different versions of some dependency, etc.
Again, I don't think Docker is very good as such, but I do think there are some ideas worth keeping, both for security and plain convenience (not often those two go hand-in-hand!)