Add configuration options to set SPICE compression settings

This spec proposes to add SPICE-related options to a Nova configuration. These options can be used to enable and set the SPICE compression settings for libvirt (QEMU/KVM) provisioned instances. Note that those options are only taken into account if SPICE support is enabled (and the VNC support is disabled).

Problem description

Sometimes, network bandwidth is limited especially if physical network hardware is involved in an OpenStack setup, e.g. if old network switches with limited uplink bandwidth are used. Nevertheless, a data-intensive transfer of console data between compute nodes and remote console clients should be possible in such an infrastructure. Here it would be beneficial if builtin compression settings could be activated for transport protocols (currently only SPICE) in order to transmit graphic-intense desktop content in networks with limited bandwidth while gaining an acceptable quality of experience (QoE).

Use Cases

  • An operator should be able to decide how to configure a desktop (console) transport via SPICE. In particular, he should be able to configure the SPICE compression algorithms and modes in order to

    • lower network bandwidth for graphical console accesses from (remote) networks with limited bandwidth. Users can benefit from such a configuration especially if they access a graphical console of an instance from home.

    • completely turn off default compression settings for local console accesses while keeping latency as low as possible within a local (wired) network. Such a configuration can be useful if users should only have local access to graphical instances for visualizing computation results.

    • select an appropriate SPICE video detection/streaming for graphic-intense use cases such as office work, media editing, and visualization of computation results, depending on the available network bandwidth and the QoE to be achieved.

  • A user should be able to access the graphical console of an instance from Horizon’s built-in spice-html5 client as before, even from (remote) networks with limited bandwidth (e.g. from home).

Proposed change

This spec proposes to add configuration options for all transport protocols in OpenStack that support the explicit activation of builtin compression settings. Currently only the integrated SPICE protocol allows the activation of various image [1] and video [2] compression settings to lower the network bandwidth while improving data transmission for graphic-intense desktops. Since SPICE is only supported by the libvirt hypervisor (through the QEMU backend), all other hypervisors and transport protocols are not affected by this proposed change. Libvirt already provides an automatic configuration of SPICE-related compression settings for the QEMU backend (see the spice documentation in the libvirt XML domain documentation [3]). Therefore, the change only requires to make the libvirt hypervisor driver capable to generate a valid libvirt XML config with activated SPICE compression settings. The OpenStack configuration for the config generation should be stored in the spice configuration group of a Nova configuration. This configuration group should be extended with configuration options that are capable of specifying the SPICE-related compression settings (choose compression algorithms and toggle compression modes on/off).



Data model impact


REST API impact


Security impact


Notifications impact


Other end user impact


Performance Impact


Other deployer impact

The following SPICE-related options will be added to the spice configuration group of a Nova configuration:

  • image_compression = [ auto_glz | auto_lz | quic | glz | lz | off ];

  • jpeg_compression = [ auto | never | always ];

  • zlib_compression = [ auto | never | always ];

  • playback_compression = [ True | False ];

  • streaming_mode = [ filter | all | off ];

Each configuration option is optional and can be set explictly to configure the associated SPICE compression setting for libvirt. If all configuration options are not set, then none of the SPICE compression settings will be configured for libvirt, which corresponds to the behavior before this proposed change. In this case, the built-in defaults from the libvirt backend (e.g. QEMU) are used.

Developer impact


Upgrade impact




Primary assignee:


Other contributors:


Feature Liaison

Feature liaison:


Work Items

  • Add SPICE-related configuration options to the Nova configuration.

  • Create documentation for the SPICE-related configuration options.

  • Extend the SPICE config generation in the libvirt hypervisor driver.




  • Implement unit tests for each function to cover testing of added and changed methods.

Documentation Impact

  • Extend the Nova configuration documentation and add documentation for the SPICE-related compression settings.




Release Name


2023.1 Antelope