I'd like to pick up on something that Matthew alluded to, although what I'm saying may not be popular. I agree that containers are compelling for cloud deployment and application scaling, and we can all be glad that container technology has progressed from the days of docker privilege escalation. I also agree that for Ceph users switching from native Ceph processes to containers carries a learning curve that could be as intimidating as learning Ceph itself. However, here is where I disagree with containerized Ceph: I worked for 19 years as a software developer for a major world-wide company. In that time, I noticed that most of the usability issues experienced by customers were due to the natural and understandable tendency for software developers to program in a way that's easy for the programmer, and in the process to lose sight of what's easy for the user. In the case of Ceph, containers make it easier for the developers to produce and ship releases. It reduces dependency complexities and testing time. But the developers aren't out in the field with their deployments when something weird impacts a cluster and the standard approaches don't resolve it. And let's face it: Ceph is a marvelously robust solution for large scale storage, but it is also an amazingly intricate matrix of layered interdependent processes, and you haven't got all of the bugs worked out yet. Just note that the beauty of software (or really of anything that is 'designed') is that a few people (developers) can produce something that a large number of people (storage administrators, or 'users') will want to use. Please remember the ratio of users (cluster administrators) to developers and don't lose sight of the users in working to ease and simplify development. -Dave -- Dave Hall Binghamton University kdhall@xxxxxxxxxxxxxx On Wed, Jun 2, 2021 at 5:37 AM Matthew Vernon <mv3@xxxxxxxxxxxx> wrote: > Hi, > > In the discussion after the Ceph Month talks yesterday, there was a bit > of chat about cephadm / containers / packages. IIRC, Sage observed that > a common reason in the recent user survey for not using cephadm was that > it only worked on containerised deployments. I think he then went on to > say that he hadn't heard any compelling reasons why not to use > containers, and suggested that resistance was essentially a user > education question[0]. > > I'd like to suggest, briefly, that: > > * containerised deployments are more complex to manage, and this is not > simply a matter of familiarity > * reducing the complexity of systems makes admins' lives easier > * the trade-off of the pros and cons of containers vs packages is not > obvious, and will depend on deployment needs > * Ceph users will benefit from both approaches being supported into the > future > > We make extensive use of containers at Sanger, particularly for > scientific workflows, and also for bundling some web apps (e.g. > Grafana). We've also looked at a number of container runtimes (Docker, > singularity, charliecloud). They do have advantages - it's easy to > distribute a complex userland in a way that will run on (almost) any > target distribution; rapid "cloud" deployment; some separation (via > namespaces) of network/users/processes. > > For what I think of as a 'boring' Ceph deploy (i.e. install on a set of > dedicated hardware and then run for a long time), I'm not sure any of > these benefits are particularly relevant and/or compelling - Ceph > upstream produce Ubuntu .debs and Canonical (via their Ubuntu Cloud > Archive) provide .debs of a couple of different Ceph releases per Ubuntu > LTS - meaning we can easily separate out OS upgrade from Ceph upgrade. > And upgrading the Ceph packages _doesn't_ restart the daemons[1], > meaning that we maintain control over restart order during an upgrade. > And while we might briefly install packages from a PPA or similar to > test a bugfix, we roll those (test-)cluster-wide, rather than trying to > run a mixed set of versions on a single cluster - and I understand this > single-version approach is best practice. > > Deployment via containers does bring complexity; some examples we've > found at Sanger (not all Ceph-related, which we run from packages): > > * you now have 2 process supervision points - dockerd and systemd > * docker updates (via distribution unattended-upgrades) have an > unfortunate habit of rudely restarting everything > * docker squats on a chunk of RFC 1918 space (and telling it not to can > be a bore), which coincides with our internal network... > * there is more friction if you need to look inside containers > (particularly if you have a lot running on a host and are trying to find > out what's going on) > * you typically need to be root to build docker containers (unlike > packages) > * we already have package deployment infrastructure (which we'll need > regardless of deployment choice) > > We also currently use systemd overrides to tweak some of the Ceph units > (e.g. to do some network sanity checks before bringing up an OSD), and > have some tools to pair OSD / journal / LVM / disk device up; I think > these would be more fiddly in a containerised deployment. I'd accept > that fixing these might just be a SMOP[2] on our part. > > Now none of this is show-stopping, and I am most definitely not saying > "don't ship containers". But I think there is added complexity to your > deployment from going the containers route, and that is not simply a > "learn how to use containers" learning curve. I do think it is > reasonable for an admin to want to reduce the complexity of what they're > dealing with - after all, much of my job is trying to automate or > simplify the management of complex systems! > > I can see from a software maintainer's point of view that just building > one container and shipping it everywhere is easier than building > packages for a number of different distributions (one of my other hats > is a Debian developer, and I have a bunch of machinery for doing this > sort of thing). But it would be a bit unfortunate if the general thrust > of "let's make Ceph easier to set up and manage" was somewhat derailed > with "you must use containers, even if they make your life harder". > > I'm not going to criticise anyone who decides to use a container-based > deployment (and I'm sure there are plenty of setups where it's an > obvious win), but if I were advising someone who wanted to set up and > use a 'boring' Ceph cluster for the medium term, I'd still advise on > using packages. I don't think this makes me a luddite :) > > Regards, and apologies for the wall of text, > > Matthew > > [0] I think that's a fair summary! > [1] This hasn't always been true... > [2] Simple (sic.) Matter of Programming > > > -- > The Wellcome Sanger Institute is operated by Genome Research > Limited, a charity registered in England with number 1021457 and a > company registered in England with number 2742969, whose registered > office is 215 Euston Road, London, NW1 2BE. > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx > _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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