This change moves the .rst files into the main adming-guide-cloud folder now conversion is complete. changes to the project config and to the openstack manuals to stop sync of .xml files are also needed. Change-Id: I498e8d6ac3cb80da413e23b14a0959abd58e7d79 Implements: blueprint reorganise-user-guides
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Configure migrations
Note
Only cloud administrators can perform live migrations. If your cloud is configured to use cells, you can perform live migration within but not between cells.
Migration enables an administrator to move a virtual-machine instance from one compute host to another. This feature is useful when a compute host requires maintenance. Migration can also be useful to redistribute the load when many VM instances are running on a specific physical machine.
The migration types are:
- Non-live migration (sometimes referred to simply as 'migration'). The instance is shut down for a period of time to be moved to another hypervisor. In this case, the instance recognizes that it was rebooted.
- Live migration (or 'true live migration'). Almost
no instance downtime. Useful when the instances must be kept running
during the migration. The different types of live migration are:
- Shared storage-based live migration. Both hypervisors have access to shared storage.
- Block live migration. No shared storage is required. Incompatible with read-only devices such as CD-ROMs and Configuration Drive (config_drive).
- Volume-backed live migration. Instances are backed by volumes rather than ephemeral disk, no shared storage is required, and migration is supported (currently only available for libvirt-based hypervisors).
The following sections describe how to configure your hosts and compute nodes for migrations by using the KVM and XenServer hypervisors.
KVM-Libvirt
Shared storage
Prerequisites
- Hypervisor: KVM with libvirt
- Shared storage:
NOVA-INST-DIR/instances/
(for example,/var/lib/nova/instances
) has to be mounted by shared storage. This guide uses NFS but other options, including the OpenStack Gluster Connector are available. - Instances: Instance can be migrated with iSCSI-based volumes.
Note
- Because the Compute service does not use the libvirt live migration functionality by default, guests are suspended before migration and might experience several minutes of downtime. For details, see :ref:Enabling True Live Migration.
- This guide assumes the default value for
instances_path
in yournova.conf
file (NOVA-INST-DIR/instances
). If you have changed thestate_path
orinstances_path
variables, modify the commands accordingly. - You must specify
vncserver_listen=0.0.0.0
or live migration will not work correctly. - You must specify the
instances_path
in each node that runs nova-compute. The mount point forinstances_path
must be the same value for each node, or live migration will not work correctly.
Example Compute installation environment
Prepare at least three servers. In this example, we refer to the servers as
HostA
,HostB
, andHostC
:HostA
is the Cloud Controller, and should run these services: nova-api, nova-scheduler,nova-network
, cinder-volume, andnova-objectstore
.HostB
andHostC
are the compute nodes that run nova-compute.
Ensure that
NOVA-INST-DIR
(set withstate_path
in thenova.conf
file) is the same on all hosts.In this example,
HostA
is the NFSv4 server that exportsNOVA-INST-DIR/instances
directory.HostB
andHostC
are NFSv4 clients that mountHostA
.
Configuring your system
Configure your DNS or
/etc/hosts
and ensure it is consistent across all hosts. Make sure that the three hosts can perform name resolution with each other. As a test, use theping
command to ping each host from one another:$ ping HostA $ ping HostB $ ping HostC
Ensure that the UID and GID of your Compute and libvirt users are identical between each of your servers. This ensures that the permissions on the NFS mount works correctly.
Export
NOVA-INST-DIR/instances
fromHostA
, and ensure it is readable and writable by the Compute user onHostB
andHostC
.For more information, see: SettingUpNFSHowTo or CentOS/Red Hat: Setup NFS v4.0 File Server
Configure the NFS server at
HostA
by adding the following line to the/etc/exports
file:NOVA-INST-DIR/instances HostA/255.255.0.0(rw,sync,fsid=0,no_root_squash)
Change the subnet mask (
255.255.0.0
) to the appropriate value to include the IP addresses ofHostB
andHostC
. Then restart the NFS server:# /etc/init.d/nfs-kernel-server restart # /etc/init.d/idmapd restart
On both compute nodes, enable the 'execute/search' bit on your shared directory to allow qemu to be able to use the images within the directories. On all hosts, run the following command:
$ chmod o+x NOVA-INST-DIR/instances
Configure NFS on
HostB
andHostC
by adding the following line to the/etc/fstab
fileHostA:/ /NOVA-INST-DIR/instances nfs4 defaults 0 0
Ensure that you can mount the exported directory
$ mount -a -v
Check that
HostA
can see theNOVA-INST-DIR/instances/
directory$ ls -ld NOVA-INST-DIR/instances/ drwxr-xr-x 2 nova nova 4096 2012-05-19 14:34 nova-install-dir/instances/
Perform the same check on
HostB
andHostC
, paying special attention to the permissions (Compute should be able to write)$ ls -ld NOVA-INST-DIR/instances/ drwxr-xr-x 2 nova nova 4096 2012-05-07 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% /var/lib/nova/instances ( <--- this line is important.)
Update the libvirt configurations so that the calls can be made securely. These methods enable remote access over TCP and are not documented here.
- SSH tunnel to libvirtd's UNIX socket
- libvirtd TCP socket, with GSSAPI/Kerberos for auth+data encryption
- libvirtd TCP socket, with TLS for encryption and x509 client certs for authentication
- libvirtd TCP socket, with TLS for encryption and Kerberos for authentication
Restart libvirt. After you run the command, ensure that libvirt is successfully restarted
# stop libvirt-bin && start libvirt-bin $ ps -ef | grep libvirt root 1145 1 0 Nov27 ? 00:00:03 /usr/sbin/libvirtd -d -l\
Configure your firewall to allow libvirt to communicate between nodes. By default, libvirt listens on TCP port 16509, and an ephemeral TCP range from 49152 to 49261 is used for the KVM communications. Based on the secure remote access TCP configuration you chose, be careful which ports you open, and always understand who has access. For information about ports that are used with libvirt, see the libvirt documentation.
You can now configure options for live migration. In most cases, you will not need to configure any options. For advanced configuration options, see the OpenStack Configuration Reference Guide <http://docs.openstack.org/ kilo/config-reference/content/list-of-compute-config-options.html #config_table_nova_livemigration>.
Enabling true live migration
Prior to the Kilo release, the Compute service did not use the
libvirt live migration function by default. To enable this function, add
the following line to the [libvirt]
section of the nova.conf
file:
live_migration_flag=VIR_MIGRATE_UNDEFINE_SOURCE,VIR_MIGRATE_PEER2PEER,VIR_MIGRATE_LIVE,VIR_MIGRATE_TUNNELLED
On versions older than Kilo, the Compute service does not use libvirt's live migration by default because there is a risk that the migration process will never end. This can happen if the guest operating system uses blocks on the disk faster than they can be migrated.
Block migration
Configuring KVM for block migration is exactly the same as the above
configuration in configuring-migrations-kvm-shared-storage
the section
called shared storage, except that NOVA-INST-DIR/instances
is local to each host rather than shared. No NFS client or server
configuration is required.
Note
- To use block migration, you must use the
--block-migrate
parameter with the live migration command. - Block migration is incompatible with read-only devices such as CD-ROMs and Configuration Drive (config_drive).
- Since the ephemeral drives are copied over the network in block migration, migrations of instances with heavy I/O loads may never complete if the drives are writing faster than the data can be copied over the network.
XenServer
Shared storage
Prerequisites
Compatible XenServer hypervisors. For more information, see the Requirements for Creating Resource Pools section of the XenServer Administrator's Guide.
Shared storage. An NFS export, visible to all XenServer hosts.
Note
For the supported NFS versions, see the NFS VHD section of the XenServer Administrator's Guide.
To use shared storage live migration with XenServer hypervisors, the hosts must be joined to a XenServer pool. To create that pool, a host aggregate must be created with specific metadata. This metadata is used by the XAPI plug-ins to establish the pool.
Using shared storage live migrations with XenServer Hypervisors
Add an NFS VHD storage to your master XenServer, and set it as the default storage repository. For more information, see NFS VHD in the XenServer Administrator's Guide.
Configure all compute nodes to use the default storage repository (
sr
) for pool operations. Add this line to yournova.conf
configuration files on all compute nodes:sr_matching_filter=default-sr:true
Create a host aggregate. This command creates the aggregate, and then displays a table that contains the ID of the new aggregate
$ nova aggregate-create POOL_NAME AVAILABILITY_ZONE
Add metadata to the aggregate, to mark it as a hypervisor pool
$ nova aggregate-set-metadata AGGREGATE_ID hypervisor_pool=true $ nova aggregate-set-metadata AGGREGATE_ID operational_state=created
Make the first compute node part of that aggregate
$ nova aggregate-add-host AGGREGATE_ID MASTER_COMPUTE_NAME
The host is now part of a XenServer pool.
Add hosts to the pool
$ nova aggregate-add-host AGGREGATE_ID COMPUTE_HOST_NAME
Note
The added compute node and the host will shut down to join the host to the XenServer pool. The operation will fail if any server other than the compute node is running or suspended on the host.
Block migration
Compatible XenServer hypervisors. The hypervisors must support the Storage XenMotion feature. See your XenServer manual to make sure your edition has this feature.
Note
- To use block migration, you must use the
--block-migrate
parameter with the live migration command. - Block migration works only with EXT local storage storage repositories, and the server must not have any volumes attached.
- To use block migration, you must use the