Moving Xen Guests to another Xen host

Shrink the LVs of Xen guest first, but before shrinking the LVM logical volumn, check its usage first
Follow this guide to shrink the LVs

http://linux-bsd-sharing.blogspot.com/2012/06/howto-shrink-size-of-ext4-lvm-logical.html

prerequisites:

create lvm on target machine
install "pv" on src machine
# apt-get install pv
run

root@src:# dd if=/dev/vg/disk bs=4096 | pv | gzip -1 | ssh -p22 targethost.org "gzip -dc | dd of=/dev/vg/disk"
on your target machine you may want to:

resize2fs if the target lvm is larger
fsck.extX /dev/vg/disk on the target machine
edit the domU.cfg according to your target machine
mount /dev/vg/disk /mnt && chroot /mnt ** edit network, hostname, hosts

Setup Fail2ban for Asterisk Verion 11.16 on Debian

INSTALL PACKAGES

Install iptables
# apt-get install iptables

Install fail2ban
# apt-get install fail2ban


SETUP


1 - Add Asterisk into fail2ban filter directory to be monitored
Create this file: /etc/fail2ban/filter.d/asterisk.conf
with the following content:

# Fail2Ban configuration file
#
#
# $Revision: 250 $
#

[INCLUDES]

# Read common prefixes. If any customizations available -- read them from
# common.local
#before = common.conf


[Definition]

#_daemon = asterisk

# Option:  failregex
# Notes.:  regex to match the password failures messages in the logfile. The
#          host must be matched by a group named "host". The tag "<HOST>" can
#          be used for standard IP/hostname matching and is only an alias for
#          (?:::f{4,6}:)?(?P<host>\S+)
# Values:  TEXT
#

# Asterisk 1.4 use the following failregex

failregex = NOTICE.* .*: Registration from '\".*\".*' failed for '<HOST>:.*' - Wrong password
# you can add more regrex here depend on log lines in /var/log/asterisk/full

2 - Now, edit the fail2ban configuration, FreePBX configuration is in /etc/fail2ban/jail.conf, so we will add these configuration info at the end of the file as here:

[asterisk-iptables]
enabled  = true
filter   = asterisk
action   = iptables-allports[name=ASTERISK, protocol=all]
           sendmail-whois[name=ASTERISK, dest=root, sender=fail2ban@example.org]
logpath  = /var/log/asterisk/full
maxretry = 4
bantime = 259200


3 - Turn it on for good

If all is well up to this point, let's make sure that fail2ban and iptables restart with the server by issuing the following commands.

Debian/Ubuntu:

update-rc.d iptables defaults
update-rc.d fail2ban defaults

You should now be somewhat protected against SIP scans and brute force attacks!

How to Clone a Xen Guest on LVM

DD Copy Method

Make the second LV for the cloned one:

lvcreate -L 5000 -n guest02 VG0

Then use dd to copy the contents of the first volume into the second. Be sure to shut down the guest01 VM before you begin:

xm shutdown guest01

Copy the contents of one LV into another:

dd if=/dev/VG0/guest01 bs=4096 of=/dev/VG0/guest02

Configure Xen

In order to make the hypervisor aware of this new guest, a new configuration file must be created. To do this, make a copy of the original configuration file:

cp /etc/xen/guest01 /etc/xen/guest02

Then, edit the new file, /etc/xen/guest02. In order for the guest to function the following lines must be changed:

• The name of the guest (from "guest01" to "guest02"
• The MAC address of the guest on the "vif =" line
• The UUID of the guest
• The logical volume on the "disk = " line.

Other parameters can also be changed as desired (the amount of memory for example). The MAC and the UUID are both random numbers. It is sufficient to simply change a few digits of each. Or, a utility that creates random MAC and UUID numbers can be used.

The new guest can now be started with the command:

xm create guest02 -c

Xen Tuning Commands

1- Resize the Xen guest Disk
Shut down the Xen guest
Resize its logical volume

Linux Commands:

# xm shutdown erp8
# lvresize /dev/VolGroup1/erp8-disk -L +1GB
# e2fsck -f /dev/VolGroup1/erp8-disk
# resize2fs /dev/VolGroup1/erp8-disk

Create new xen guest on DOM0

SSH to DOM0 (Xen host machine)

and run this statement to create one:

# sudo xen-create-image --hostname=myhost --memory=512mb --swap=1024mb --vcpus=2 --pygrub --dist=wheezy

Which is will run Debian Wheezy

RAM 512

SWAP 1024

vcpus number is 2

How To Remove Xen Guest from DOM0

1 - SSH into the Dom0 (the host machine).

2 -
$ xm list | grep <DomU> 
where <DomU> is the short hostname of the virtual machine, e.g. yoyodyne. The DomU to be decommissioned should not be listed. If it is, execute

$ xm destroy <DomU> 
This command force shutdowns the VM

3 - Remove the auto-boot symlink:
$ rm /etc/xen/auto/<DomU>.cfg 

4 - Remove the Xen domain configuration:
$ rm /etc/xen/<DomU>.cfg 

5 - Remove all logical volumes associated with the domU. In most cases this will consist of a single LV:
lvremove /dev/<Dom0>/<DomU>-<device> 

For example:
lvremove /dev/dom0server/yoyodyne.example.com-hda

Process events, functions in Background in Odoo / OpenERP by using cron

In Odoo / OpenERP, sometime we have to wait for a while when we press on a button. We have to wait after all processes completed. Like a Send Mail button, after pressing Send Mail button we have to wait program to send out the email, as long as work is in not done the openerp UI is blocked.
We can escape this waitting. In Odoo / OpenERP, we can have our processes run in background, by using ir.cron of OpenERP like this way:

Example:
In function _let_process_in_backrgound which is invoked by our button, we use a cron task, the cron task will call method:  'function': 'do_something', of model: 'model': 'hr_timesheet_sheet.sheet' (for example), agurments are:


def _let_process_in_backrgound(self, cr, uid, data, context = {}):
    timesheet_id = 1
    str_now = datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
    nextcall = parser.parse(str_now) + datetime.timedelta(seconds = 60)
    pool.get('ir.cron').create(cr, uid, {
                'name': 'Cron job to do something that take very long time',
                'user_id': uid,
                'model': 'hr_timesheet_sheet.sheet',
                'function': 'do_something',
                'nextcall': nextcall,
                'args': repr([timesheet_id])
            })
    return {}


In Odoo / OpenERP, we have the method do_something like this:

def do_something(self, cr, uid, timesheet_id):
    ....
    ....
    return True

By this way we created a cron task in OpenERP to be executed at nextcall time.