Using live migration feature

Overview of this feature

OS: Ubuntu lucid 10.04/10.10 (both instances and host).
Shared strorage: The NOVA-INST-DIR/instances directory of nova-computes have to be mounted same shared storage(tested using NFS)
Instances : Instance can be migrated with ISCSI/AoE based volumes.
Hypervisor: KVM with libvirt
("NOVA-INST-DIR/instance" is expected that vm image is put on to. see "flags.instances_path" in nova.compute.manager for the default value)

Sample Nova Installation before starting

Prepare 3 Ubuntu lucid 10.04/10.10 host at least, lets say, HostA, HostB, HostC
nova-api/nova-network/nova-volume/nova-objectstore/nova-scheduler(and other daemon) are running on HostA.
nova-compute is running on both HostB and HostC.
All nova daemon runs as root.
HostA export NOVA-INST-DIR/instances, HostB and HostC mount it.
To avoid any confusion, NOVA-INST-DIR is same at HostA/HostB/HostC("NOVA-INST-DIR" shows top of install dir) .
HostA export NOVA-INST-DIR/instances, HostB and HostC mount it.
detail description is below.

Pre-requisite settings

(a) /etc/hosts setting at HostA/HostB/HostC

Make sure 3 Hosts can name-resolution with each other. ping with each other is better way to test.

ping HostA
ping HostB
ping HostC

(b) NFS settings at HostA. add the below desctiption to /etc/exports.

NOVA-INST-DIR/instances HostA/255.255.0.0(rw,sync,fsid=0,no_root_squash

Change "255.255.0.0" appropriate netmask, which should include HostB/HostC. Then restart nfs server.

/etc/init.d/nfs-kernel-server restart
/etc/init.d/idmapd restart

Also, at any compute nodes, add below line to /etc/fstab:

HostA:/ DIR nfs4 defaults 0 0

Then try to mount at compute node. Check exported directory is successfully mounted.

mount -a -v

If fail, try this at any hosts.

iptables -F

Also, check file/daemon permissions. We expect any nova daemons are running as root.

root@openstack2-api:/opt/nova-2010.4# ps -ef | grep nova
root 5948 5904 9 11:29 pts/4 00:00:00 python /opt/nova-2010.4//bin/nova-api
root 5952 5908 6 11:29 pts/5 00:00:00 python /opt/nova-2010.4//bin/nova-objectstore
... (snip)

"NOVA-INST-DIR/instances/" directory can be seen at HostA:

root@openstack:~# ls -ld NOVA-INST-DIR/instances/
drwxr-xr-x 2 root root 4096 2010-12-07 14:34 nova-install-dir/instances/

Also, at HostB and HostC:

# ls -ld NOVA-INST-DIR/instances/
drwxr-xr-x 2 root root 4096 2010-12-07 14:34 nova-install-dir/instances/

# df -k
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1            921514972   4180880 870523828   1% /
none                  16498340      1228  16497112   1% /dev
none                  16502856         0  16502856   0% /dev/shm
none                  16502856       368  16502488   1% /var/run
none                  16502856         0  16502856   0% /var/lock
none                  16502856         0  16502856   0% /lib/init/rw
HostA:        921515008 101921792 772783104  12% /opt  ( <--- this line is important.)

(b) libvirt settings (Necessary to use simple tcp (qemu+tcp://)).

Modify /etc/libvirt/libvirt.conf :

before : #listen_tls = 0
after : listen_tls = 0

before : #listen_tcp = 1
after : listen_tcp = 1

Adding following line to /etc/libvirt/libvirt.conf :

auth_tcp = "none"

Modify /etc/init/libvirt-bin.conf

 before : exec /usr/sbin/libvirtd -d
 after : exec /usr/sbin/libvirtd -d -l

Modify modify /etc/default/libvirt-bin

before :libvirtd_opts=" -d"
after :libvirtd_opts=" -d -l"

then, restart libvirt

# stop libvirt-bin && start libvirt-bin ps -ef | grep libvirt

Make sure you get the below result.

# /opt/nova-2010.2# ps -ef | grep libvirt
root 1145 1 0 Nov27 ? 00:00:03 /usr/sbin/libvirtd -d -l

if you would like to use qemu+ssh, change "live_migration_uri" flag at nova.vir.libvirt_conn and make appropriate settings described at http://libvirt.org/.

Usage

To get a list of physical hosts,
- nova-manage service list
To get a available pysical resource of each host,
- nova-manage host shows hostname
- An example result is below. The 1st line shows total amount of resource that the specified host has. The 2nd and latter lines show usage resource per project. This command is created because admins can decide which host should be a destination of live migration.

HOST PROJECT cpu mem(mb) disk(gb)
openstack2-c2 16 32232 878 > openstack2-c2 admin 1 2048 20

For live migration,
- nova-manage instances live_migration ec2-id(i-xxxx) destination-host-name.
- Once this command is executed, admins will check the status through euca-describe-instances. The status is changed from 'running' to 'migrating', and changed to 'running' when live migration finishes. Note that it depends on an environment how long it takes to live migration finishes. If it finishes too fast, admins cannot see 'migrating' status.

# euca-describe-instances
Reservation:r-qlg3favp
RESERVATION r-qlg3favp adminINSTANCE i-2ah453 ami-tiny 12.1.0.14 10.0.0.3
migrating testkey (admin, openstack2-c2) 0 m1.small 2010-11-28 16:09:16

When live migration finishes successfully, admin can check the part of euca-describe-instances which shows physical node information. ( only when euca-describe-instances is executed by admin user ) Admins also can check live migration source compute node logfile which may show a log.

Live migration i-xxxx to DESTHOST finishes successfully.

Trouble shooting

When live migration fails somehow, error messages are shown at:
- scheduler logfile
- source compute node logfile
- dest compute node logfile

Obsolete:LiveMigrationUsage