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Migrating Xen domainU Guests Between Host Systems

1,023 bytes added, 18:52, 29 May 2016
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<td width="20%">[[Xen Monitoring Tools and Techniques|Previous]]<td align="center">[[Xen Virtualization Essentials|Table of Contents]]<td width="20%" align="right">[[Solving Common Xen Problems|Next]]</td>
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<td width="20%">Xen Monitoring Tools and Techniques<td align="center"><td width="20%" align="right">Solving Common Xen Problems</td>
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One of the most compelling features of Xen virtualization is the ability to migrate a domainU guest from one host system to another. Of particular significance, however, is Xen's ability to perform live migrations whereby a running guest domainU system is moved from one system to another such that there is only an imperceptible interruption in service. In this chapter we will discuss the requirements for performing live Xen domainU migrations before walking through an example live migration.
* The two systems need to be running compatible versions of Xen.
* Firewalls Firewall settings (and SELinux if enabled) must be configured to permit communication between the source and destination hosts.
* Both systems must be configured to allow migration of virtual machines.
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Secondly, the ''xend-relocation-hosts-allow'' value must be changed to define the hosts from which relocation requests will be accepted. This can be a list of hostnames or IP addresses including wildcards. An empty value may also be specified (somewhat insecurely) to accept connections from any host. The following example allows migration requests only from a host with an IP address of 192.168.2.20:
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(xend-relocation-hosts-allow '192.168.2.20')
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In order to resolve this problem it is essential that the firewall on the destination host be configured to allow TCP traffic on either port 8002 or , if the default value was not used, the port number specified for ''xend-relocation-port'' in the ''/etc/xen/xend-config.sxp'' files if the default value was not usedfile.
== Preparing the Xen Migration Environment ==
The next requirement for performing live migrations involves the creation of a Xen domainU guest to migrate. For the purposes of this chapter, we will use a disk image based domainU guest environment installed in the ''/xen'' directory of a server. The steps required to create such a guest are outlined in detail in the chapter entitled [[Building a Xen Virtual Guest Filesystem on a Disk Image (Cloning Host System)]], which will instruct you provides steps on how to create and configure the following files:
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== Checking the Xen Log for Migration Errors ==
The migration from a user's perspective is a silent process. This can make tracking down problems difficult since a failed migration will often not report anything on the command-line. If problems are encountered during the migration the first place to look for information is the Xen log file which can be viewed by running the ''xm log'' command. The following shows partial output from a successful live migration:
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VmError: I need 524288 KiB, but dom0_min_mem is 262144 and shrinking to 262144 KiB would leave only 248744 KiB free.
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<hr>
<table border="0" cellspacing="0" width="100%">
<tr>
<td width="20%">[[Xen Monitoring Tools and Techniques|Previous]]<td align="center">[[Xen Virtualization Essentials|Table of Contents]]<td width="20%" align="right">[[Solving Common Xen Problems|Next]]</td>
<tr>
<td width="20%">Xen Monitoring Tools and Techniques<td align="center"><td width="20%" align="right">Solving Common Xen Problems</td>
</table>

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