While there are many reasons containerization helps, I'll just touch on one real quick that is relevant to the conversation. Orchestration. Implementing orchestration of an entire clustered software with many different: * package managers * dependency chains * init systems * distro specific quirks * configuration management systems has over the years proven intractable. Each project cant implement all permutations of each of those with high quality. Which is especially important in a data storage system. Good orchestration of complex systems before containers was very rare. Finding two that you wanted to use, that supported the same base systems was even more rare. Standardizing on containers allow orchestration to be performed without concern to those things, making it significantly easier to write good orchestration that is usable by a broad audience. Such as cephadm. rook-ceph takes it to another level IMO and only requires managing just the orchestration bits that are specific to ceph over the base orchestration layer, k8s. So even more orchestration layer can be shared between the devs and the admins. This allows admins to generalize their skills even more. Yes, its another thing to learn. but its worth it in the long term IMO. Being able to quickly deploy ceph, elasticsearch, and greenplum clusters and deal with the day two issues with ease is something that hasn't been a thing before. Yes, its a big shift from the traditional distro philosophy. But the advanced orchestration abilities possible once we step outside the traditional linux distro really is game changing. ________________________________________ From: Matthew Vernon <mv3@xxxxxxxxxxxx> Sent: Wednesday, June 2, 2021 2:36 AM To: ceph-users@xxxxxxx Subject: Why you might want packages not containers for Ceph deployments Check twice before you click! This email originated from outside PNNL. 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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