Using HTTP to interact with XenServer¶
XenServer exposes an HTTP interface on each host, that can be used to perform various operations. This chapter describes the available mechanisms.
VM Import and Export¶
Because the import and export of VMs can take some time to complete, an asynchronous HTTP interface to the import and export operations is provided. To perform an export using the XenServer API, construct an HTTP GET call providing a valid session ID, task ID and VM UUID, as shown in the following pseudo code:
task = Task.create() result = HTTP.get(server, 80, "/export?session_id=session_id&task_id=task_id&ref=vm_uuid");
For the import operation, use an HTTP PUT call as demonstrated in the following pseudo code:
task = Task.create() result = HTTP.put(server, 80, "/import?session_id=session_id&task_id=task_id&ref=vm_uuid");
Getting XenServer Performance Statistics¶
XenServer records statistics about the performance of various aspects of your XenServer installation. The metrics are stored persistently for long term access and analysis of historical trends. Where storage is available to a VM, the statistics are written to disk when a VM is shut down. Statistics are stored in RRDs (Round Robin Databases), which are maintained for individual VMs (including the control domain) and the server. RRDs are resident on the server on which the VM is running, or the pool master when the VM is not running. The RRDs are also backed up every day.
In earlier versions of the XenServer API, instantaneous performance metrics could be obtained using the
host_metricsmethods and associated methods. These methods has been deprecated in favor of using the http handler described in this chapter to download the statistics from the RRDs on the VMs and servers. Note that by default the legacy metrics will return zeroes. To revert to periodic statistical polling as present in earlier versions of XenServer, set the
other-config:rrd_update_interval=intervalparameters on your host to one of the following values, and restart your host:
never : This is the default, meaning no periodic polling is performed.
1 : Polling is performed every 5 seconds.
2 : Polling is performed every minute.
By default, the older metrics APIs will not return any values, and so this key must be enabled to run monitoring clients which use the legacy monitoring protocol.
Statistics are persisted for a maximum of one year, and are stored at different granularities. The average and most recent values are stored at intervals of:
5 seconds for the past 10 minutes
one minute for the past 2 hours
one hour for the past week
one day for the past year
RRDs are saved to disk as uncompressed XML. The size of each RRD when written to disk ranges from 200KiB to approximately 1.2MiB when the RRD stores the full year of statistics.
If statistics cannot be written to disk, for example when a disk is full, statistics will be lost and the last saved version of the RRD will be used.
Statistics can be downloaded over HTTP in XML format, for example using
wget. See rrddump
and rrdxport for
information about the XML format. HTTP authentication can take the form
of a username and password or a session token. Parameters are appended
to the URL following a question mark (?) and separated by ampersands
To obtain an update of all VM statistics on a host, the URL would be of the form:
This request returns data in an rrdtool
xport style XML format, for
every VM resident on the particular host that is being queried. To
differentiate which column in the export is associated with which VM,
legend field is prefixed with the UUID of the VM.
To obtain host updates too, use the query parameter
The step will decrease as the period decreases, which means that if you request statistics for a shorter time period you will get more detailed statistics.
Additional rrd_updates parameters¶
cf= ave|min|max: the data consolidation mode
interval= interval: the interval between values to be reported
By default only
avestatistics are available. To obtain
maxstatistics for a VM, run the following command:xe pool-param-set uuid=pool_uuid other-config:create_min_max_in_new_VM_RRDs
To obtain all statistics for a host:
To obtain all statistics for a VM: