config: Shift Linux-namespace no-tweaking rule to a generic rule #540
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There are more background references for the Linux-namespaces no-tweaking rule in 01c2d55 (config-linux: Extend no-tweak requirement to runtime namespaces, 2016-08-24, opencontainers#538). But the old rule's: > ... error out if the config specifies anything else related to that > namespace. was overly broad. For example, it arguably blocked you from setting network interface priorities for interfaces belonging to an old network namespace even if you were setting those priorities in a new cgroup (because the interfaces and therefore priorities for them are related to the old network namespace). The new rule tries to apply the spirit of the old rule ("don't touch things that already exist") more generally so we have a consistent approach that clearly *does* allow you to configure a new cgroup without having to care about new/old namespaces. I'm personally fine with join-and-tweak, but the maintainer consensus is that it's too complicated to allow (at least for now) [1,2]. [1]: opencontainers#158 Subject: Clarify behavior around namespaces paths [2]: opencontainers#537 (comment) Subject: [linux] Tweaking host namespaces? Signed-off-by: W. Trevor King <[email protected]>
| While the following are invalid: | ||
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| * A Linux configuration that sets [`hostname`](#hostname) but does not create a new [UTS namespace](config-linux.md#namespaces). | ||
| * A Linux configuration that sets [network limits][config-linux.md#network] with an existing [control group][config-linux.md#control-groups]. |
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How to judge a cgroup is an existing one or a new one?
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On Fri, Aug 26, 2016 at 01:24:04AM -0700, Ma Shimiao wrote:
+* A Linux configuration that sets [network limits][config-linux.md#network] with an existing [control group][config-linux.md#control-groups].
How to judge a cgroup is an existing one or a new one?
If cgroupsPath is absolute, you can require no cgroups to exist at
that relative path from the controller mount points 1. You can also
compare cgroupsPath with values set for other running containers 2,
if you happen to know which other containers are running and which
runtime was used to launch them. In other cases, external tooling
like ocitools should probably skip this test.
Runtimes creating a container, on the other hand, have an easy way to
tell: they're using a new cgroup if they try to mkdir the leaf group
and it does not return EEXIST or other error.
This was referenced Sep 18, 2016
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This restriction originally landed via 02b456e (Clarify behavior around namespaces paths, 2015-09-08, opencontainers#158). The hostname case landed via 66a0543 (config: Require a new UTS namespace for config.json's hostname, 2015-10-05, opencontainers#214) citing the namespace restriction. The restriciton extended to runtime namespaces in 01c2d55 (config-linux: Extend no-tweak requirement to runtime namespaces, 2016-08-24, opencontainers#538). There was a proposal in-flight to get config-wide consistency around the no-tweaking concept [1]. In today's meeting, the maintainer consensus was to strike the no-tweaking restriction [2], which is what I've done here. The hostname entry still mentions the UTS namespace to provide a guard against accidental foot-gunning. There was no no-tweaking language for properties related to other namespaces (e.g. 'mounts'). Maybe the other namespaces have more obvious names. [1]: opencontainers#540 [2]: http://ircbot.wl.linuxfoundation.org/meetings/opencontainers/2017/opencontainers.2017-01-11-22.04.log.html#l-117 Signed-off-by: W. Trevor King <[email protected]>
wking
added a commit
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Jan 11, 2017
This restriction originally landed via 02b456e (Clarify behavior around namespaces paths, 2015-09-08, opencontainers#158). The hostname case landed via 66a0543 (config: Require a new UTS namespace for config.json's hostname, 2015-10-05, opencontainers#214) citing the namespace restriction. The restriciton extended to runtime namespaces in 01c2d55 (config-linux: Extend no-tweak requirement to runtime namespaces, 2016-08-24, opencontainers#538). There was a proposal in-flight to get config-wide consistency around the no-tweaking concept [1]. In today's meeting, the maintainer consensus was to strike the no-tweaking restriction [2], which is what I've done here. I've removed the ROADMAP entry because this gives folks a way to adjust existing containers (launch a new container which joins and tweaks the original). The hostname entry still mentions the UTS namespace to provide a guard against accidental foot-gunning. There was no no-tweaking language for properties related to other namespaces (e.g. 'mounts'). Maybe the other namespaces have more obvious names. [1]: opencontainers#540 [2]: http://ircbot.wl.linuxfoundation.org/meetings/opencontainers/2017/opencontainers.2017-01-11-22.04.log.html#l-117 Signed-off-by: W. Trevor King <[email protected]>
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There are more background references for the Linux-namespaces no-tweaking rule in 01c2d55 (config-linux: Extend no-tweak requirement to runtime namespaces, 2016-08-24, #538). But the old rule's:
was overly broad. For example, it arguably blocked you from setting network interface priorities for interfaces belonging to an old network namespace even if you were setting those priorities in a new cgroup (because the interfaces and therefore priorities for them are related to the old network namespace).
The new rule tries to apply the spirit of the old rule (“don't touch things that already exist”) more generally so we have a consistent approach that clearly does allow you to configure a new cgroup without having to care about new/old namespaces.
I'm personally fine with join-and-tweak, but the maintainer consensus is that it's too complicated to allow (at least for now, some folks want it).