Using Xen with Entropy

This document describes the necessary steps to use Entropy with the Xen hypervisor . For this version, we use the version 3.2.1 of Xen (the debian package for the distribution lenny). This document does not discuss about the compilation and the installation of Xen and we suppose that each node run the Xen hypervisor and the Domain-0.

Domain-0 and Entropy

The Domain-0 is a particular virtual machine. In the context of Entropy, it comes from the impossibility to migrate this domain. This situation has some consequences when we want to use Entropy with Xen.

We choose to exclude the Domain-0 from the pool of virtual machines to manage. However, we cannot ignore that it consumes some resources. At this moment, we suppose that its CPU consumption is neglictible but we consider its memory consumption.

When we use Xen as Hypervisor, we choose to remove the Domain-0 from the list of virtual machines to manage and to reduce the total amount of memory usuable for the virtual machines by the amount of memory allocated to the Domain-0. These considerations appears during the monitoring.

The xen migration driver:

Before using the migration driver, you have to check that the relocation server is enabled and allows incoming migrations. Check this in /etc/xen/xend-config.sxp :

(xend-relocation-server yes)
(xend-relocation-address '')
(xend-relocation-hosts-allow '')
(xend-relocation-port 8002)

The migration driver uses the HTTP interface of xend. Thus, the HTTP server must be enabled and accepting migration requests from Entropy. Check this in /etc/xen/xend-config.sxp :

#Enable the HTTP server
(xend-http-server yes) 
#Binding address from the HTTP server (here, it listening on all the addresses)
(xend-address '')
#Listening port
(xend-port 8000)

At this moment, the relocation port must be 8002, the migrations are performed in live and the HTTP server must be listening on the port 8000.

Warning : As Xen is only focused on the migration of the state of the virtual machine, you have to provide a shared storage management system that supports the live migration, such as NFS server, iSCSI, DRDB, ...