> Subordinate charms only make sense when collocated. And I would argue that subordinates are extremely common, at least in production environments.
> In this context clean up is very important because it's not unusual for > operators to switch technologies. For example replace telegraf with node-exporter or collectd. With that in mind, I'd like to reiterate one of my original questions: how do we handle cleanup in the case where two or more colocated charms have the same dependencies? In the case of background services, do we not stop & disable them? Do we stop & disable them and expect the remaining charms to repair the situation? On Thu, Oct 20, 2016 at 3:32 AM, Jacek Nykis <jacek.ny...@canonical.com> wrote: > On 19/10/16 16:15, Marco Ceppi wrote: > >> 2. Don't colocate units if at all possible. In separate containers on > the > >> same machine, sure. But there's absolutely no guarantee that colocated > >> units won't conflict with each other. What you're asking about is the > very > >> problem colocation causes. If both units try to take over the same > port, or > >> a common service, or write to the same file on disk, etc... the results > >> will very likely be bad. Stop hooks should clean up everything they > >> started. Yes, this may break other units that are colocated, but the > >> alternative is leaving machines in a bad state when they're not > colocated. > >> > > > > Colocation is a rare scenario, a more common one is manual provider. > > Subordinate charms only make sense when collocated. And I would argue > that subordinates are extremely common, at least in production > environments. > > In any production deployment I expect some form of monitoring (nrpe, > telegraf). Many deployments will also use logstash-forwarder, > landscape-client, ntp, container-log-archive and other subordinate charms. > > So you are looking at 3-4 or more services on each juju machine, > including LXC/LXD guests and manually provisioned systems. > > In this context clean up is very important because it's not unusual for > operators to switch technologies. For example replace telegraf with > node-exporter or collectd. > > Regards, > Jacek > >
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