[lxc-devel] Q: general lxc architecture

Wed Nov 11 20:30:27 UTC 2009

Andrian Nord wrote:
>  On Tue, Nov 10, 2009 at 09:40:46PM +0100, Daniel Lezcano wrote:
> > * finish with the /var/lxc/* cleanup and maybe change lxc-create
> > and lxc-destroy to a simple wrapper script doing roughly cp and rm.
> >
>  Heh, just like I'm doing now (copying 'template' container, that
>  sed'ing config and fstab as s/template/<container>/) - maybe it make
>  some sense not to rm -Rf container config directory, but silently
>  move it to .<container>.destroyed, as vzctl does, so it could be
>  reused if container whould be ressurected (or user may just simply rm
>  -Rf it himself).

I don't see the point of resurrecting a destroyed container.

>  Still, if you want to just copy container, you need the source,
>  which, theoretically, should be user-modifitable. It could be some
>  hardcoded path/name or, maybe, do you plan something like global
>  lxc.conf config?

What I have in mind is to just copy the file somewhere with lxc-create 
and remove it with lxc-destroy. And, much more later, integrate in a 
nicer way lxc-debian, lxc-sshd, lxc-fedora, lxc-busybox, etc ...

> > / * launch containers without creating it (not persistent in the
> > system).
>  I.e. autocreating following some hardcoded defaults inside memory,
>  without producing corresponding disc structures? And how it will be
>  controlled by user, if he want to have other defaults? Or you mean
>  ability of start-time changing of particular config options,
>  following user to specify something like lxc-execute -n lxc.temporary
>  --hostname ssh.example.com /usr/sbin/sshd where 'lxc.temporary' is
>  name of some persistent configuration, which is loaded as defaults?

Not exactly.

1) You created the container before, lxc-start/lxc-execute use the 
configuration.
2) You didn't create the container before, lxc-start/lxc-execute use the 
configuration file specified in the command line (if none specified, 
then default values).

eg.  lxc-start/lxc-execute -f <config> -n mycontainer -- /bin/bash

At present, this is what happens more or less because when you call 
lxc-execute and the container does not exist, it is created before and 
destroyed after. In case of failure, (machine crash, lxc bug, kill -9), 
the container is not destroyed.

And I think it is much more simple to keep a single generic 
configuration to pass it to several lxc-start/lxc-execute instead of 
creating them before. But that do not prevent the create the containers 
before to keep a persistent configuration for a specific container. Both 
behavior are kept.

> > * check and fix the lxc-debian and lxc-sshd to match the recent
> > modifications around the /var/lxc/*
>  And lxc-netstat, it assumes that initpid contained into
>  ${lxcroot}/${name}/initpid

Aha, good point ! To be fixed :)

> > Yes, that makes sense with the cleanup of /var/lxc. But there are
> > some clarifications to do around the owner of a container. eg.
> > shall we let only root to create the containers and assign
> > permissions to it so a non-root user can use it ?
>
>  Hm, at least this is configurable by root. He may specify some
>  write-group for lxcpath, of for some specific containers only. Or he
>  may just make a simple sed+echo script and give sudo on it for
>  specific users =)

I think that makes sense to let root to create a container and assign 
the permissions.
That can be added in the lxc-create script.

> > I am fine with this patch, is it tested ? Shall I take it ?
>
>  When i've posted it i'd tested that it at compiles and changes
>  LXCPATH correctly. Now I've tested it more - with this patch and
>  copied configs all my 16 containers succesfully were restarted. So it
>  works.

Cool, thanks.

>  But, maybe it will be also usefull to move than all contents that are
>  installed currently into /etc/lxc/ (examples) into
>  ${docdir}/examples, where they should be, theoretically?

Yes.

>  Here comes additional patch for that. I don't sure if we really need
>  another configure switch for examples, but some distros like to
>  provide documentation themselfs, i.e. with additional compression, so
>  this could be useful for them.
>
>  Also, if everyone in agreement, that /etc/lxc/ is better placement
>  for configurations, maybe it could be done as default? It will break
>  backward compability, but everyone who uses git version must be
>  awared of such things and next release will probably need some
>  migration-tool anyway.

I would like to keep the actual default and let the different distro 
maintainers to change that in their spec files and add a post-install 
script to move the existing containers from /var/lxc to /etc/lxc. When 
everyone moved to /etc then we can change the default.
As I specified in the man page of lxc, I don't guarantee, until version 
1.0.0 is reached, the compatibility between version. Of course, that 
don't prevent us to take care of that in the changes ;)

lxc is not yet stable enough (in terms of api / cli syntax / behaviour), 
to plan a migration tool.

>  Also, if you are planning to have some general lxc-utils' config (say
>  /etc/lxc/lxc.conf), maybe lxcpath should be pointed at
>  /etc/lxc/containers/ or something like that? (I'm currently using
>  /etc/lxc/common/ directory for internal use, i.e. for common for
>  containers configuration files that are bind'ed into container and
>  symliked at their systems path)
>
>  Patch moves etc/* contents into doc/examples/ and adds
>  --disable-examples configure switch which may be used not to install
>  examples. Default is to install them into ${docdir}/examples
>  (commonly: /usr/share/doc/lxc/examples)
>
>  Signed-off-by: Andrian Nord <NightNord at gmail.com>
>
>  diff --git a/Makefile.am b/Makefile.am index 3933d2a..90b771b 100644
>  --- a/Makefile.am +++ b/Makefile.am @@ -2,8 +2,8 @@
>
>  ACLOCAL_AMFLAGS = -I config
>
>  -SUBDIRS = src etc scripts doc -DIST_SUBDIRS = config src etc scripts
>  doc +SUBDIRS = src scripts doc +DIST_SUBDIRS = config src scripts doc
>  EXTRA_DIST = autogen.sh lxc.spec CONTRIBUTING MAINTAINERS ChangeLog
>
>  pcdatadir = $(datadir)/pkgconfig diff --git a/configure.ac
>  b/configure.ac index 5e4ac46..66f9b1b 100644 --- a/configure.ac +++
>  b/configure.ac @@ -25,6 +25,12 @@ fi
>
>  AM_CONDITIONAL([ENABLE_DOCBOOK], [test "x$have_docbook" = "xyes"])
>
>  +AC_ARG_ENABLE([examples], +    [AC_HELP_STRING([--disable-examples],
>  [do not install configuration examples])], +    [],
>  [enable_examples=yes]) + +AM_CONDITIONAL([ENABLE_EXAMPLES], [test
>  "x$enable_examples" = "xyes"]) + AS_AC_EXPAND(PREFIX, $prefix)
>  AS_AC_EXPAND(LIBDIR, $libdir) AS_AC_EXPAND(BINDIR, $bindir) @@
>  -107,13 +113,13 @@ AC_CONFIG_FILES([ src/lxc/lxc-setcap
>  src/lxc/lxc-version
>
>  -    etc/Makefile -    etc/lxc-macvlan.conf -    etc/lxc-no-netns.conf -
>  etc/lxc-empty-netns.conf -    etc/lxc-phys.conf -    etc/lxc-veth.conf -
>  etc/lxc-complex-config +    doc/examples/Makefile +
>  doc/examples/lxc-macvlan.conf +    doc/examples/lxc-no-netns.conf +
>  doc/examples/lxc-empty-netns.conf +    doc/examples/lxc-phys.conf +
>  doc/examples/lxc-veth.conf +    doc/examples/lxc-complex-config ])
>  AC_CONFIG_COMMANDS([default],[[]],[[]]) AC_OUTPUT diff --git
>  a/doc/Makefile.am b/doc/Makefile.am index 9f7bf69..bd96c99 100644 ---
>  a/doc/Makefile.am +++ b/doc/Makefile.am @@ -1,3 +1,5 @@ +SUBDIRS =
>  examples +DIST_SUBDIRS = examples
>
>  EXTRA_DIST = \ FAQ.txt \ diff --git a/doc/examples/Makefile.am
>  b/doc/examples/Makefile.am new file mode 100644 index
>  0000000..0490a8b --- /dev/null +++ b/doc/examples/Makefile.am @@ -0,0
>  +1,21 @@ +EXTRA_DIST = $(pkgexamples_DATA) + +if ENABLE_EXAMPLES
>  +pkgexamplesdir=$(docdir)/examples + +pkgexamples_DATA = \ +
>  lxc-macvlan.conf \ +    lxc-no-netns.conf \ +    lxc-empty-netns.conf \ +
>  lxc-phys.conf \ +    lxc-veth.conf \ +    lxc-complex-config +endif +
>  +noinst_DATA = \ +    lxc-macvlan.conf.in \ +    
lxc-empty-netns.conf.in \
>  +    lxc-no-netns.conf.in \ +    lxc-phys.conf.in \ +    
lxc-veth.conf.in \ +
>  lxc-complex-config.in diff --git a/doc/examples/lxc-complex-config
>  b/doc/examples/lxc-complex-config

Oops, you moved a wrong one :)

Thanks
  -- Daniel