Citrix Hypervisor 8.2

Using HTTP to interact with Citrix Hypervisor

Citrix Hypervisor 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 Citrix Hypervisor Management 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");
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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");
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Getting Citrix Hypervisor Performance Statistics

Citrix Hypervisor records statistics about the performance of various aspects of your Citrix Hypervisor 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.

Warning

In earlier versions of the Citrix Hypervisor Management API, instantaneous performance metrics could be obtained using the VM_metrics, VM_guest_metrics, host_metrics classes 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 Citrix Hypervisor, set the other-config:rrd_update_interval=interval parameters 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.

Warning

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:

http://username:password@host/rrd_updates?start=secondssinceepoch

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, the legend field is prefixed with the UUID of the VM.

To obtain host updates too, use the query parameter host=true:

http://username:password@host/rrd_updates?start=secondssinceepoch&host=true

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

Note:

By default only ave statistics are available. To obtain min and max statistics 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:

http://username:password@host/host_rrd

To obtain all statistics for a VM:

http://username:password@host/vm_rrd?uuid=vm_uuid
Using HTTP to interact with Citrix Hypervisor