Re:Docker isn't perfect – Issue #216
by cwyers on Thursday August 27, 2015 @05:48PM
(#10132348)
Or put another way. The kernel is deprecating multi-writer support for cgroups at some point in the future. systemd has announced they will provide an API for cgroups, where systemd serves as the single writer. On systems not using systemd, some other service will have to serve as the single writer for cgroups. They may or may not implement the same API. (I don't know that anyone has announced plans for an alternative to systemd's cgroups API.) Once this changeover happens, systemd's API will be the only way to use cgroups on systemd systems. This isn't portable, but that's not a problem with Red Hat's contributions to Docker, it's an issue with systemd. Kicking RHEL's contributors to Docker out doesn't actually solve this problem.
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> it's an issue with systemd
I wouldn't even say this is an issue with systemd. It just happens that systemd (or logind actually) is what was selected as the cgroup controller on distributions that use it.
Mostly, it's an issue with Docker (and all other cgroup clients) that are currently using their own controllers.
It doesn't matter one bit what the distributions chose as their new controller, the existing clients would need to adapt to the new environment.
If anything, having systemd handle this has simplified their jobs significantly since they can support a huge swath of distributions capturing the overwhelming majority of user's systems by targeting a single API.