Nova and DevStack

This is a rough guide to various configuration parameters for nova running with DevStack.


In Juno, nova implemented a spec to allow read/write access to the serial console of an instance via nova-serialproxy.

The service can be enabled by adding n-sproxy to ENABLED_SERVICES. Further options can be enabled via local.conf, e.g.

# Options defined in nova.cmd.serialproxy

# Host on which to listen for incoming requests (string value)

# Port on which to listen for incoming requests (integer
# value)

# Options defined in nova.console.serial

# Enable serial console related features (boolean value)
# Do not set this manually.  Instead enable the service as
# outlined above.

# Range of TCP ports to use for serial ports on compute hosts
# (string value)

# Location of serial console proxy. (string value)

# IP address on which instance serial console should listen
# (string value)

# The address to which proxy clients (like nova-serialproxy)
# should connect (string value)

Enabling the service is enough to be functional for a single machine DevStack.

These config options are defined in nova.conf.serial_console.

For more information on OpenStack configuration see the OpenStack Compute Service Configuration Reference

Fake virt driver

Nova has a fake virt driver which can be used for scale testing the control plane services or testing “move” operations between fake compute nodes, for example cold/live migration, evacuate and unshelve.

The fake virt driver does not communicate with any hypervisor, it just reports some fake resource inventory values and keeps track of the state of the “guests” created, moved and deleted. It is not feature-complete with the compute API but is good enough for most API testing, and is also used within the nova functional tests themselves so is fairly robust.


Set the following in your devstack local.conf:


The NUMBER_FAKE_NOVA_COMPUTE variable controls the number of fake nova-compute services to run and defaults to 1.

When VIRT_DRIVER=fake is used, devstack will disable quota checking in nova and neutron automatically. However, other services, like cinder, will still enforce quota limits by default.


The actual value to use for NUMBER_FAKE_NOVA_COMPUTE depends on factors such as:

  • The size of the host (physical or virtualized) on which devstack is running.

  • The number of API workers. By default, devstack will run max($nproc/2, 2) workers per API service. If you are running several fake compute services on a single host, then consider setting API_WORKERS=1 in local.conf.

In addition, while quota will be disabled in neutron, there is no fake ML2 backend for neutron so creating fake VMs will still result in real ports being created. To create servers without networking, you can specify --nic=none when creating the server, for example:

$ openstack --os-compute-api-version 2.37 server create --flavor cirros256 \
    --image cirros-0.6.2-x86_64-disk --nic none --wait test-server


--os-compute-api-version greater than or equal to 2.37 is required to use --nic=none.

To avoid overhead from other services which you may not need, disable them in your local.conf, for example:

disable_service horizon
disable_service tempest