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vzctl questions about hooking [message #31322]

Tue, 24 June 2008 18:39

jleggett
Messages: 2
Registered: June 2008

Junior Member

Hi...

We're trying to interface some configuration management tools with OpenVZ to streamline creation and use of containers.

I am making some assumptions here that when making a container with vzctl it does some parsing of the template.tar.gz to try and determine the OS being used as said template. For example for my test I used a centos-5-i386-minimal example so from that I assume it reads the centos.conf file to determine what shell scripts to execute? These map too:

ADD_IP=redhat-add_ip.sh
DEL_IP=redhat-del_ip.sh
SET_HOSTNAME=redhat-set_hostname.sh
SET_DNS=set_dns.sh
SET_USERPASS=set_userpass.sh
SET_UGID_QUOTA=set_ugid_quota.sh
POST_CREATE=postcreate.sh

My first question: Can I replace these shell scripts with any executable program to garner the same data as long as my return values match up to what vzctl expects? Is there any documentation for this interfacing?

I modifed the redhat-add_ip.sh script to call #!/bin/bash -x to output bash debug lines, and expected them to be either to STDOUT or /var/log/vzctl.log but I see that output in neither, so where is it called and when?

Does the OpenVZ community consider it better to directly manipulate the container data under /vz/private/CTID or is their a prime imperative to use the built in OpenVZ provided tools?

It *seems* like I could just use standard configuration management (cfengine, puppet, etc) tools to configure the container since I can write to the area of the filesystem, but
I am worried about what i don't know at this point before executing that.

Thanks in advance to replies, suggestions, comments, pointers.

Jeff Leggett

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Re: vzctl questions about hooking [message #31362 is a reply to message #31322]

Wed, 25 June 2008 16:01

kir
Messages: 1645
Registered: August 2005
Location: Moscow, Russia

Senior Member

Hi Jeff,

This is src/lib/dist.c, because all such "setting" scripts are distro-dependent, and in src/lib/vps_configure.c (because we used to call a VE a VPS).

Set of script to be run is determined by an /etc/vz/dist/$NAME.conf, where $NAME is taken from the value of OSTEMPLATE parameter of VE config file (/etc/vz/conf/$VEID.conf). Note that the value of OSTEMPLATE is taken literally first, then everything after and including the last '-' is taken out and tried again, and so on until the config file is found. If a per-distro config file is not found (say, due to bad OSTEMPLATE value), default (DIST_CONF_DEF defined in include/dist.h) is used. See get_dist_conf_name() in src/lib/dist.c for details.

After the per-distro config file is found it it read and dist_actions struct is filled in. Now vzctl knows which scripts to call. Names of scripts in file are relative to /etc/vz/dists/scripts directory.

Now, when a "set" action is run, appropriate scripts are called:

  src/vzctl-actions.c: set() calls
     src/lib/res.c vps_setup_res() calls
        src/lib/vps_configure.c vps_configure() calls
            specific action scripts one by one, using
                /src/lib/exec.c vps_exec_script() function

I suggest to use some code traversing tools such as vim + ctags to navigate all this, or gdb.

Now to your direct questions

Quote:

Can I replace these shell scripts with any executable program to garner the same data as long as my return values match up to what vzctl expects? Is there any documentation for this interfacing?

Yes you can, if you place your stuff to under /etc/vz/conf/dists/scripts and make it executable.

Documentation describing all the scripts is in vzctl sources here (vzctl with those changes are not yet released):
http://git.openvz.org/?p=vzctl;a=blob;f=etc/dists/distribution.conf-template

Quote:

I modifed the redhat-add_ip.sh script to call #!/bin/bash -x to output bash debug lines, and expected them to be either to STDOUT or /var/log/vzctl.log but I see that output in neither, so where is it called and when?

you can do something like this:

#/bin/bash

# Enable bash debugging
set -x
# Define the log file
LOGFILE=/tmp/my-$$.log
# Redirect both stdout and stderr to $LOGFILE
exec >$LOGFILE 2>&1

echo 1

If you only want to redirect stderr (and thus bash debugging messages) use the following exec instead:

exec 2>$LOGFILE

Then, see your $LOGFILE _inside_ a VE (because the script is run inside a VE to improve security).

Quote:

Does the OpenVZ community consider it better to directly manipulate the container data under /vz/private/CTID or is their a prime imperative to use the built in OpenVZ provided tools?

It doesn't matter really, just make sure to not screw up mixing both ways Smile

Kir Kolyshkin

http://static.openvz.org/userbars/openvz-developer.png

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Re: vzctl questions about hooking [message #31571 is a reply to message #31362]

Thu, 03 July 2008 16:32

jleggett
Messages: 2
Registered: June 2008

Junior Member

Good information, and it got me farther... But I still have some oddities

It would appear that these scripts get run before init? My tools are complaining abut lack of certain files in /proc within the VE but if I run same tools after entering the VE they run fine.

[Updated on: Thu, 03 July 2008 16:32]

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