To install:
apt install mypackage
systemctl edit mypackage
[Service]
CPUAccounting=true
CPUQuota=200%
MemoryAccounting=true
MemoryHigh=500M
systemctl enable --now mypackage
--cpus 2 --memory 500M
One thing you have not covered is filesystem isolation, which docker also does very easily. There is a lot to configure on the systemd side[0] and the parts that are overlapping are just easier to configure and run with docker. Systemd is the better tool to build repeatable installs for pet processes, but again, there is a lot of knowledge underneath that is related. People to this day still complain that systemd does too much (I personally like it a lot, and it's great to have everything in one place).
[EDIT] Just to make myself clear, systemd is an amazing tool -- I like it, I run it, I'm not smart enough to administer a more complicated setup -- but docker is easier, for a large part of the small subset of systemd's capabilities that docker covers.
--cpus 2 --memory 500mb
If I want to run a useful piece of software like redis let's say, but I want to run it with a resource constraint to make sure that it doesn't take more than 2CPUs and 500MB of memory, it is far easier to do that with the following command line:
docker run --rm redis --cpus 2 --memory 500mb -p 6379:6379
Docker won because of it's developer ergonomics (containers weren't new), systemd won because of it's feature set, convenience and sturdiness. They're different tools with different primary use-cases.
As a (former) developer I d rather ran redis in a container during development, but for production I d rather rely on boring VMs unless some scaling is required. (Managed k8s case set apart)
Agree, but my view on this is that the implicit answer of how you do all that (i.e. the file system, syslog) is now gone. There will be pain (complexity) in the short term, but at the end of the day, we're going to be able to build much better orchestration and systems. To kind of restate that, before you had to worry where a process wrote out it's output (stdout? /var/log/<program>? /etc/<program>/logs? /home/<user>/<program>/logs? syslog?), now you know want to get the non-stdout/stderr logs of the thing you're running, you'd better give it a volume to write to (which may be fake, and actually write everything to some remote storage or something), and I think that's a step forward.
Of course, I'm not saying containers should go everywhere -- relying on boring VMs over containers is fine too -- but I think rich world of functionality available to container-driven workflows is popular for good and bad reasons, and the good reasons are worth exploring/beneficial to me.
I thought the kernel has virtual memory and if you consume more it will swap some memory and thats it.
Couldnt you just manage memory from inside your app? if its redis, then check the db size and shutdown/cleanup gracefully, and not crash redis with OOM?
> I thought the kernel has virtual memory and if you consume more it will swap some memory and thats it.
Well just to make sure the right memory goes to the right places -- if someone uploads a large file and you've made a mistake in your code that tries to hold it all in memory instead of buffering it straight to disk for example, you'd want that process to crash, and not your machine.
Also you generally don't want to swap, so much so that Kubernetes disables it immediately[0]. Not that Google is the only group with the right answer but they seem to think nothing can come of a machine having to swap. Maybe they're right. Even if they're not, A world where one service swaps[1] (I've never done this with docker to try it though) is probably better than one where it uses all the memory and everything swaps.
> Couldnt you just manage memory from inside your app? if its redis, then check the db size and shutdown/cleanup gracefully, and not crash redis with OOM?
You'd be surprised -- some languages just don't have a way to very easily get feedback from GC[2]. It's also something that I don't think most people think about, messing with the -XmXx<setting>s in Java is definitely year 2/3/4 java development for most people.
[0]: https://github.com/kubernetes/kubernetes/issues/53533
[1]: https://docs.docker.com/config/containers/resource_constrain...
Wow, given how expensive RAM is it is no surprise they will never allow kubernetes work with swap, becausr it directly translates to $$$ for GCP and other cloud providers. Also since everyone loves using Java/Spring/Node and other memory hungry frameworks - it print enormous $ for cloud providers to require users overallocate RAM and disable swap.
or am I just spitballing conspiracy theory here and there is no conflict btw decisions like these and vendors' revenue streams?
contrast it to Ops mentality of software is a cattle (here is your memory quota and if its OOM, just kill/restart the service and hope next run it wont run OOM)
Restated, my point here is that while containers can be more complex and have pitfalls (a lot of which have been worked out somewhat at this point), there is no complexity free lunch -- `[docker|podman|crictl] run --rm --cpus 2 --memory 500mb ...` is pretty darn easy, and more so than writing properly portable and well-considered systemd unit files (and putting them in the right place, with the right permissions, under the right slice, etc). It's easier than most of the options out there (including the old methods of per-user resource segregation).