[lxc-devel] lxc-clone rewrite
Stéphane Graber
stgraber at ubuntu.com
Fri Sep 4 17:47:11 UTC 2015
On Fri, Sep 04, 2015 at 07:42:50PM +0200, Christian Brauner wrote:
> On Fri, Sep 04, 2015 at 01:11:14PM -0400, Stéphane Graber wrote:
> > On Fri, Sep 04, 2015 at 04:21:42PM +0200, Christian Brauner wrote:
> > > On Fri, Sep 04, 2015 at 02:04:29PM +0000, Serge Hallyn wrote:
> > > > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > > > On Mon, Aug 31, 2015 at 09:53:03PM +0200, Christian Brauner wrote:
> > > > > > On Mon Aug 31, 2015 at 04:08:33PM +0000, Serge Hallyn wrote:
> > > > > > > Quoting Stéphane Graber (stgraber at ubuntu.com):
> > > > > > > > On Mon, Aug 31, 2015 at 01:43:07PM +0000, Serge Hallyn wrote:
> > > > > > > > > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > > > > > > > > On Fri, Aug 28, 2015 at 12:46:17AM +0200, Christian Brauner wrote:
> > > > > > > > > > > On Thu, Aug 27, 2015 at 03:41:03PM -0400, Stéphane Graber wrote:
> > > > > > > > > > > > On Sun, Aug 16, 2015 at 04:46:31PM +0000, Serge Hallyn wrote:
> > > > > > > > > > > > > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > > > > > > > > > > > Hey,
> > > > > > > > > > > > >
> > > > > > > > > > > > > I'll leave this to Stéphane, as he's pretty keen on leaving the #
> > > > > > > > > > > > > commands
> > > > > > > > > > > > > low. As you say we might eventually be able to deprecate
> > > > > > > > > > > > > lxc-clone,
> > > > > > > > > > > > > and
> > > > > > > > > > > > > lxc-copy might eventually be a nice hook for migration.
> > > > > > > > > > > >
> > > > > > > > > > > > That'd be fine with me I think, bonus point if we can somehow merge
> > > > > > > > > > > > lxc-start-ephemeral in there and kill two birds with one stone
> > > > > > > > > > > > (lxc-clone & lxc-start-ephemeral).
> > > > > > > > > > > >
> > > > > > > > > > > > The timeline for this would be having lxc-copy in 1.2 with both
> > > > > > > > > > > > lxc-clone and lxc-start-ephemeral doing arg swapping + re-exec
> > > > > > > > > > > > tricks
> > > > > > > > > > > > with a warning that they'll go away for good in 2.0.
> > > > > > > > > > > >
> > > > > > > > > > > > How does that sound?
> > > > > > > > > > >
> > > > > > > > > > > Sounds good! I'm on it!
> > > > > > > > > > >
> > > > > > > > > > > Christian
> > > > > > > > > >
> > > > > > > > > > In the current python implementation of lxc-start-ephemeral we generate
> > > > > > > > > > a
> > > > > > > > > > pre-mount and post-stop script. The post-stop script seems to be used to
> > > > > > > > > > destroy
> > > > > > > > > > the container. For the rewrite in C and the merge with lxc-clone I
> > > > > > > > > > thought
> > > > > > > > > > about
> > > > > > > > > > using a simple snapshot-clone with c->clone() with a random name, start
> > > > > > > > > > it
> > > > > > > > > > c->start() and when the container is shutdown destroy it with
> > > > > > > > > > c->destroy().
> > > > > > > > > > This seems cleaner to me then generating scripts. Are there any reasons
> > > > > > > > > > to
> > > > > > > > > > not
> > > > > > > > > > do it this way? And if so what would you prefer?
> > > > > > > > >
> > > > > > > > > If you can do this robustly and cleanly then I prefer this.
> > > > > > > >
> > > > > > > > The reason was that the container could be started backgrounded (-d) in
> > > > > > > > which case lxc-start-ephemeral wasn't around anymore to clean things up
> > > > > > > > when the container exits.
> > > > > > > >
> > > > > > > > The post-stop method ensured that the container would be destroyed
> > > > > > > > whenever it finally dies and regardless of how it was killed (either
> > > > > > > > shutdown from inside the container or lxc-stop/lxc-destroy).
> > > > > > >
> > > > > > > Right, so to do this without post-stop we'd probably have to hack a special
> > > > > > > case into the reboot: loop around container-start. Maybe even hardcode the
> > > > > > > 'transient' case into the lxc_handler struct. Or just have a 'special'
> > > > > > > post-stop hook (doesn't even have to be a script, just a hard-code value
> > > > > > > checked for before we run the script) telling us 'delete this thing'.
> > > > > > >
> > > > > > > It could end up looking nice, or could end up a mess. I reserve final
> > > > > > > judgement until there's code :)
> > > > > > Agreed. Let's see how mess-less I can code this.
> > > > > >
> > > > > > As long as the container is started in foreground mode the container will be
> > > > > > destroyed regardless of whether it was killed by lxc-stop or shutdown from
> > > > > > inside. The only problematic case is when the container is started daemonized.
> > > > > >
> > > > > > I need to think about how to handle that case for a bit. I'd like to code more
> > > > > > than one option I think. Unless there's need for rush. :) Suggestions of course
> > > > > > welcome.
> > > > > I'm currently in favour of the lxc.hook.post-stop version for daemonized
> > > > > containers. The rest means fiddling with a lot of the api-functions for the
> > > > > a rather special case. But there are two things I would like to have input
> > > > > about:
> > > > >
> > > > > 1) Should we register ephemeral clone-snapshots in the lxc_snapshots file of the
> > > > > original container? (I would think not.)
> > > >
> > > > If for instance it is a overlayfs based snapshot, and you allow the parent
> > > > to be deleted, then the ephemeral container will misbehave. I'm pretty
> > > > sure that's the case now and I haven't heard any complaints, but it is
> > > > non-ideal.
> > > >
> > > > > 2) Should we have an additional state TRANSIENT in addition to RUNNING,
> > > > > STARTING, etc.?
> > > >
> > > > What exactly would it mean? STARTING is already inherently TRANSIENT. Would
> > > > TRANSIENT mean 'building but not yet starting'?
> > > I was unclear. TRANSIENT or EPHEMERAL in the sense of "this is a running
> > > container but it will be deleted once it is shutdown". So when you do work on a
> > > container and you're unsure whether it is an ephemeral container you could check
> > > with lxc-info -n NAME and see TRANSIENT or EPHEMERAL and know "this thing is
> > > going to be deleted when I shut it down."
> >
> > It seems to me like this has the potential to break a fair amount of
> > existing tools which wait for "RUNNING" before interacting with a
> > container. If we were to have multiple "RUNNING" equivalent state, we
> > ought to add a new exported function that'd check whether the container
> > is running regardless of the state's name but requiring the use of this
> > would only be possible when we break backward compatibility (so LXC
> > 2.0).
>
> Agreed!.
>
> >
> > I suspect a cleaner way would be to have a config option for ephemeral
> > containers, something like lxc.ephemeral=1 that will cause LXC to
> > destroy the container when it dies and can be used by API clients to
> > query whether a container is ephemeral.
>
> I actually already done that. I just need to bring it in final shape. But here
> is a sneak-preview so you can stop me if you'd rather have it a different way.
> And thanks for all the feedback and quick answers!
>
> PRELIMINARY: Destroy ephemeral overlayfs container
I personally prefer ephemeral as a name, if only because that's what
we've been using for years in both LXC and LXD, so one less thing to
confuse people with :)
>
> ---
> src/lxc/conf.h | 3 +++
> src/lxc/confile.c | 16 ++++++++++++++++
> src/lxc/start.c | 14 ++++++++++++++
> 3 files changed, 33 insertions(+)
>
> diff --git a/src/lxc/conf.h b/src/lxc/conf.h
> index dc5328a..6e75713 100644
> --- a/src/lxc/conf.h
> +++ b/src/lxc/conf.h
> @@ -370,6 +370,9 @@ struct lxc_conf {
> * should run under when using lxc-execute */
> uid_t init_uid;
> gid_t init_gid;
> +
> + /* transient */
> + int transient;
> };
>
> #ifdef HAVE_TLS
> diff --git a/src/lxc/confile.c b/src/lxc/confile.c
> index ca3b8d8..356d85f 100644
> --- a/src/lxc/confile.c
> +++ b/src/lxc/confile.c
> @@ -108,6 +108,8 @@ static int config_environment(const char *, const char *, struct lxc_conf *);
> static int config_init_cmd(const char *, const char *, struct lxc_conf *);
> static int config_init_uid(const char *, const char *, struct lxc_conf *);
> static int config_init_gid(const char *, const char *, struct lxc_conf *);
> +static int config_transient(const char *key, const char *value,
> + struct lxc_conf *lxc_conf);
>
> static struct lxc_config_t config[] = {
>
> @@ -176,6 +178,7 @@ static struct lxc_config_t config[] = {
> { "lxc.init_cmd", config_init_cmd },
> { "lxc.init_uid", config_init_uid },
> { "lxc.init_gid", config_init_gid },
> + { "lxc.transient", config_transient },
> };
>
> struct signame {
> @@ -2490,6 +2493,8 @@ int lxc_get_config_item(struct lxc_conf *c, const char *key, char *retv,
> return lxc_get_conf_int(c, retv, inlen, c->init_uid);
> else if (strcmp(key, "lxc.init_gid") == 0)
> return lxc_get_conf_int(c, retv, inlen, c->init_gid);
> + else if (strcmp(key, "lxc.transient") == 0)
> + return lxc_get_conf_int(c, retv, inlen, c->transient);
> else return -1;
>
> if (!v)
> @@ -2759,3 +2764,14 @@ bool network_new_hwaddrs(struct lxc_conf *conf)
> }
> return true;
> }
> +
> +static int config_transient(const char *key, const char *value,
> + struct lxc_conf *lxc_conf)
> +{
> + int v = atoi(value);
> +
> + lxc_conf->transient = v;
> +
> + return 0;
> +}
> +
> diff --git a/src/lxc/start.c b/src/lxc/start.c
> index ffb8d12..e551ca4 100644
> --- a/src/lxc/start.c
> +++ b/src/lxc/start.c
> @@ -495,6 +495,20 @@ void lxc_fini(const char *name, struct lxc_handler *handler)
> close(handler->ttysock[0]);
> close(handler->ttysock[1]);
> }
> + if (handler->conf->transient > 0) {
> + char *check_rootfs = handler->conf->rootfs.path;
> + if (strncmp(check_rootfs, "overlayfs:", 10) == 0) {
> + int ret;
> + char destroy[MAXPATHLEN];
> + ret = snprintf(destroy, MAXPATHLEN, "%s/%s", handler->lxcpath, name);
> + if (ret < 0)
> + ERROR("Error creating string");
> + INFO(destroy);
> + ret = lxc_rmdir_onedev(destroy, NULL);
> + if (ret < 0)
> + ERROR("Destroying container failed");
> + }
> + }
> cgroup_destroy(handler);
> free(handler);
> }
> --
> 2.5.1
>
--
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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