4 ms·

Yep, and you'd generally expect to spend time understanding the complexity that systemd brings, the subsystems that power it, and how you can separate resources

Yep, and you'd generally expect to spend time understanding the complexity that systemd brings, the subsystems that power it, and how you can separate resources there! There is no free lunch. 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).

c0l0 6y ago
I don't see how appending --cpus 2 --memory 500mb to the argument vector liberates these options' definer from "understanding [...] the subsystems that power it", and reflect on their potential impact. And I'd argue that THIS is the real complexity incurred by these kinds of resource constraints that seem so simple on the surface - not the specific syntax or location you have to use to introduce them. All of which makes systemd unit files and their settings' implications (which are amazingly well-documented btw) as good as any other option, imho.
- hardwaresofton 6y ago
  Systemd is great software -- it is useful, and powerful. A systemd unit file, the idea of what a unit is, when they run, how they run, what shells they use, what permissions they run under, and lots of other complexities are expressed as options in the unit file, configuration files on the system, and in other places. 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 Than to write the equivalent systemd unit file, set up the isolated filesystems that docker would let you easily bind mount in, etc. This is like comparing systemd-nspawn to systemd -- if systemd-nspawn isn't simpler than systemd then what are we even doing. 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.
  - hartmel 6y ago
    Then you will want to manage the configuration file and to browse logs, and you ll have to mount files to you container. And your deployment start to reimplement (a subset to your needs) what distros did System integration complexity didn't disappear thanks to containers. It was just moved to another place. I dd add that, being convenient for developers doesn't mean it's convenient for hosting management. At the end, when one side convenience is taken in consideration, it often translate to complexity and pain at the other side. K8S become in some companies more a mandatory runtime requirement than a hosting commodity/facility. 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)
    - hardwaresofton 6y ago
      > Then you will want to manage the configuration file and to browse logs, and you ll have to mount files to you container. And your deployment start to reimplement (a subset to your needs) what distros did System integration complexity didn't disappear thanks to containers. 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.
  - slt2021 6y ago
    can anyone explain why you might need to limit memory consumption of your service? 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?
SahAssar 6y ago
Let's say you are installing this from a normal package manager and want to limit it: To install: apt install mypackage To edit the systemd unit (automatically creating the file in the right place): systemctl edit mypackage Then add these lines to limit to 2 cpus and 500mb memory: [Service] CPUAccounting=true CPUQuota=200% MemoryAccounting=true MemoryHigh=500M And then to start it now and on boot: systemctl enable --now mypackage This is now integrated with package updates, starts on boot, logs to the same place that most other system utilities do and so on.
- hardwaresofton 6y ago
  I'm not about to argue against systemd, it's great software, and it's in every distro right now for a reason. Understanding apt (+/- how to package for it), systemctl, and the options you've laid out in your unit file are not trivial, and I would argue that they are less trivial (or harder) than understanding what's happening with containers, especially if you're running rootless containers, and/or using a container tool like podman which does without the daemon. --cpus 2 --memory 500M is easier, and gets you the same results though they may not be as permanent or as well managed -- the management and external stuff is an orthogonal concern, and that's not the situation I was addressing. The original point was insinuating that throwing up a binary and getting it to run. your filesystem is also not available to the container by default, and in this way docker sort of fails closed. If you're running a rootless container, the story is even better. 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. [0]: https://www.redhat.com/sysadmin/mastering-systemd https://www.redhat.com/sysadmin/mastering-systemd
- aequitas 6y ago

c0l0 6y ago

I don't see how appending --cpus 2 --memory 500mb to the argument vector liberates these options' definer from "understanding [...] the subsystems that power it", and reflect on their potential impact. And I'd argue that THIS is the real complexity incurred by these kinds of resource constraints that seem so simple on the surface - not the specific syntax or location you have to use to introduce them. All of which makes systemd unit files and their settings' implications (which are amazingly well-documented btw) as good as any other option, imho.

hardwaresofton 6y ago
Systemd is great software -- it is useful, and powerful. A systemd unit file, the idea of what a unit is, when they run, how they run, what shells they use, what permissions they run under, and lots of other complexities are expressed as options in the unit file, configuration files on the system, and in other places. 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 Than to write the equivalent systemd unit file, set up the isolated filesystems that docker would let you easily bind mount in, etc. This is like comparing systemd-nspawn to systemd -- if systemd-nspawn isn't simpler than systemd then what are we even doing. 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.
- hartmel 6y ago
  Then you will want to manage the configuration file and to browse logs, and you ll have to mount files to you container. And your deployment start to reimplement (a subset to your needs) what distros did System integration complexity didn't disappear thanks to containers. It was just moved to another place. I dd add that, being convenient for developers doesn't mean it's convenient for hosting management. At the end, when one side convenience is taken in consideration, it often translate to complexity and pain at the other side. K8S become in some companies more a mandatory runtime requirement than a hosting commodity/facility. 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)
  - hardwaresofton 6y ago
    > Then you will want to manage the configuration file and to browse logs, and you ll have to mount files to you container. And your deployment start to reimplement (a subset to your needs) what distros did System integration complexity didn't disappear thanks to containers. 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.
- slt2021 6y ago
  can anyone explain why you might need to limit memory consumption of your service? 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?

SahAssar 6y ago

Let's say you are installing this from a normal package manager and want to limit it: To install: apt install mypackage To edit the systemd unit (automatically creating the file in the right place): systemctl edit mypackage Then add these lines to limit to 2 cpus and 500mb memory: [Service] CPUAccounting=true CPUQuota=200% MemoryAccounting=true MemoryHigh=500M And then to start it now and on boot: systemctl enable --now mypackage This is now integrated with package updates, starts on boot, logs to the same place that most other system utilities do and so on.

hardwaresofton 6y ago
I'm not about to argue against systemd, it's great software, and it's in every distro right now for a reason. Understanding apt (+/- how to package for it), systemctl, and the options you've laid out in your unit file are not trivial, and I would argue that they are less trivial (or harder) than understanding what's happening with containers, especially if you're running rootless containers, and/or using a container tool like podman which does without the daemon. --cpus 2 --memory 500M is easier, and gets you the same results though they may not be as permanent or as well managed -- the management and external stuff is an orthogonal concern, and that's not the situation I was addressing. The original point was insinuating that throwing up a binary and getting it to run. your filesystem is also not available to the container by default, and in this way docker sort of fails closed. If you're running a rootless container, the story is even better. 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. [0]: https://www.redhat.com/sysadmin/mastering-systemd https://www.redhat.com/sysadmin/mastering-systemd
aequitas 6y ago