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Zero-Downtime Migration

Starting with Virtuozzo Containers 3.0, the vzmigrate utility allows you to migrate your Containers from one Hardware Node to another with zero downtime. The zero downtime migration technology has the following main advantages as compared with the standard one:

Note: Zero-downtime migration cannot be performed on Containers having one or several opened sessions established with the vzctl enter CT_ID command.

Before performing zero-downtime migration, it is recommended to synchronize the system time on the Source and Destination Nodes, e.g. by means of NTP (http://www.ntp.org). The reason for this recommendation is that some processes running in the Container might rely on the system time being monotonic and thus might behave unpredictably if they see an abrupt step forward or backward in the time once they find themselves on the new Node with different system clock parameters.

In the current version of Virtuozzo Containers, you can make use of the following types of zero-downtime migration:

To migrate a Container by using the zero downtime migration technology, you should pass the --online option to the vzmigrate utility. By default, the iterative online migration type is used to move a Container from one Hardware Node to another. For example, you can migrate Container 101 from the current Hardware Node to the Destination Node named my_node.com by executing the following command:

Note: If the CPU capabilities on the Source Node exceed those on the Destination Node (e.g. you migrate from a Source Node running the Pentium 4 processor to a Destination Node running the Pentium 3 processor), the migration may fail and you will be presented with the corresponding warning message. However, if you are sure that the CPU power on the Destination Node is sufficient to start and run the Container(s) being migrated, you can use the -f option to force the migration process.

# vzmigrate --online --require-realtime my_node.com 101

Enter password:

Connection to destination Hardware Node (192.168.1.57) \

is successfully established

Moving/copying Container#101 -> Container#101, [], [] ...

Syncing private area '/vz/private/101'

- 100% |***************************************

done

Suspending Container#101 ...

done

Dumping Container#101 ...

done

...

Migration completed

The --require--realtime option tells vzmigrate to move the Container by using the iterative online migration type only. So, if this migration type cannot be carried out for some reason or other, the command will fail and exit. If this option is omitted and in the case of failure while performing the iterative migration, vzmigrate will try to move your Container by means of the simple online migration type or the lazy online migration type (if the --lazy option is given). You can specify more than one Container ID simultaneously; in this case, all specified Containers will be moved to a new Hardware Node one by one.

If you wish to use another migration type for moving your Containers to another Node, you should additionally pass certain options to vzmigrate:

To migrate one or more Containers in Parallels Management Console, select these Containers from the list in the right pane after selecting the Containers item in the left pane. Then right-click the selection and point to Tasks --> Migrate to Another Hardware Node on the context menu. Note that the target Hardware Node must be already registered in Parallels Management Console; otherwise, the migration option will not be available. A migration dialog appears, for example:

Management Console - Migrating Containers

In this window you can do the following:

When you are ready, click the Migrate button.

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