In Salt 0.14.0, an advanced cloud control system was introduced, allowing private cloud VMs to be managed directly with Salt. This system is generally referred to as Salt Virt.
The Salt Virt system already exists and is installed within Salt itself. This means that besides setting up Salt, no additional salt code needs to be deployed.
libvirt python module and the
certtool binary are required.
The main goal of Salt Virt is to facilitate a very fast and simple cloud that can scale and is fully featured. Salt Virt comes with the ability to set up and manage complex virtual machine networking, powerful image and disk management, and virtual machine migration with and without shared storage.
This means that Salt Virt can be used to create a cloud from a blade center and a SAN, but can also create a cloud out of a swarm of Linux Desktops without a single shared storage system. Salt Virt can make clouds from truly commodity hardware, but can also stand up the power of specialized hardware as well.
The first step to set up the hypervisors involves getting the correct software installed and setting up the hypervisor network interfaces.
Salt Virt is made to be hypervisor agnostic but currently, the only fully implemented hypervisor is KVM via libvirt.
The required software for a hypervisor is libvirt and kvm. For advanced features, install libguestfs or qemu-nbd.
Libguestfs and qemu-nbd allow for virtual machine images to be mounted before startup and get pre-seeded with configurations and a salt minion.
This sls will set up the needed software for a hypervisor, and run the routines to set up the libvirt pki keys.
Package names and setup used is Red Hat specific. Different package names will be required for different platforms.
libvirt: pkg.installed:  file.managed: - name: /etc/sysconfig/libvirtd - contents: 'LIBVIRTD_ARGS="--listen"' - require: - pkg: libvirt virt.keys: - require: - pkg: libvirt service.running: - name: libvirtd - require: - pkg: libvirt - network: br0 - libvirt: libvirt - watch: - file: libvirt libvirt-python: pkg.installed:  libguestfs: pkg.installed: - pkgs: - libguestfs - libguestfs-tools
The hypervisors will need to be running a network bridge to serve up network devices for virtual machines. This formula will set up a standard bridge on a hypervisor connecting the bridge to eth0:
eth0: network.managed: - enabled: True - type: eth - bridge: br0 br0: network.managed: - enabled: True - type: bridge - proto: dhcp - require: - network: eth0
Salt Virt comes with a system to model the network interfaces used by the
deployed virtual machines. By default, a single interface is created for the
deployed virtual machine and is bridged to
br0. To get going with the
default networking setup, ensure that the bridge interface named
on the hypervisor and is bridged to an active network device.
To use more advanced networking in Salt Virt, read the Salt Virt Networking document:
One of the challenges of deploying a libvirt based cloud is the distribution
of libvirt certificates. These certificates allow for virtual machine
migration. Salt comes with a system used to auto deploy these certificates.
Salt manages the signing authority key and generates keys for libvirt clients
on the master, signs them with the certificate authority, and uses pillar to
distribute them. This is managed via the
libvirt state. Simply execute this
formula on the minion to ensure that the certificate is in place and up to
The above formula includes the calls needed to set up libvirt keys.
Salt Virt requires that virtual machine images be provided as these are not generated on the fly. Generating these virtual machine images differs greatly based on the underlying platform.
Virtual machine images can be manually created using KVM and running through the installer, but this process is not recommended since it is very manual and prone to errors.
Virtual Machine generation applications are available for many platforms:
Once virtual machine images are available, the easiest way to make them
available to Salt Virt is to place them in the Salt file server. Just copy an
/srv/salt and it can now be used by Salt Virt.
For purposes of this demo, the file name
centos.img will be used.
Many existing Linux distributions distribute virtual machine images which can be used with Salt Virt. Please be advised that NONE OF THESE IMAGES ARE SUPPORTED BY SALTSTACK.
These images have been prepared for OpenNebula but should work without issue with Salt Virt, only the raw qcow image file is needed: https://wiki.centos.org/Cloud/OpenNebula
With hypervisors set up and virtual machine images ready, Salt can start issuing cloud commands using the virt runner.
Start by running a Salt Virt hypervisor info command:
This will query the running hypervisor(s) for stats and display useful information such as the number of CPUs and amount of memory.
You can also list all VMs and their current states on all hypervisor nodes:
Now that hypervisors are available a virtual machine can be provisioned, the
virt.init routine will create a new virtual machine:
salt-run virt.init centos1 2 512 salt://centos.img
The Salt Virt runner will now automatically select a hypervisor to deploy
the new virtual machine on. Using
salt:// assumes that the CentOS virtual
machine image is located in the root of the Salt File Server on the master.
When images are cloned (i.e. copied locally after retrieval from the file
server), the destination directory on the hypervisor minion is determined by the
virt:images config option; by default this is
When a VM is initialized using
virt.init, the image is copied to the
cp.cache_file and will be mounted and seeded with a minion.
Seeding includes setting pre-authenticated keys on the new machine. A minion
will only be installed if one can not be found on the image using the default
The biggest bottleneck in starting VMs is when the Salt Minion needs to be installed. Making sure that the source VM images already have Salt installed will GREATLY speed up virtual machine deployment.
You can also deploy an image on a particular minion by directly calling the
virt execution module with an absolute image path. This can be quite handy for
salt 'hypervisor*' virt.init centos1 2 512 image=/var/lib/libvirt/images/centos.img
Now that the new VM has been prepared, it can be seen via the
This command will return data about all of the hypervisors and respective virtual machines.
Now that the new VM is booted, it should have contacted the Salt Master. A
test.ping will reveal if the new VM is running.
For fast image cloning, you can use the qcow disk image format.
enable_qcow flag and a .qcow2 image path to virt.init:
salt 'hypervisor*' virt.init centos1 2 512 image=/var/lib/libvirt/images/centos.qcow2 enable_qcow=True start=False
Beware that attempting to boot a qcow image too quickly after cloning
can result in a race condition where libvirt may try to boot the machine
before image seeding has completed. For that reason, it is recommended to
Also know that you must not modify the original base image without
first making a copy and then rebasing all overlay images onto it.
qemu-img rebase usage docs.
Salt Virt comes with full support for virtual machine migration. Using the libvirt state in the above formula makes migration possible.
A few things need to be available to support migration. Many operating systems turn on firewalls when originally set up; the firewall needs to be opened up to allow for libvirt and kvm to cross communicate and execution migration routines. On Red Hat based hypervisors in particular, port 16514 needs to be opened on hypervisors:
iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 16514 -j ACCEPT
More in-depth information regarding distribution specific firewall settings can be found in:
Salt also needs the
virt:tunnel option to be turned on. This flag tells Salt
to run migrations securely via the libvirt TLS tunnel and to use port 16514.
virt:tunnel, libvirt tries to bind to random ports when running
To turn on
virt:tunnel, simply apply it to the master config file:
virt: tunnel: True
Once the master config has been updated, restart the master and send out a call to the minions to refresh the pillar to pick up on the change:
salt \* saltutil.refresh_modules
Now, migration routines can be run! To migrate a VM, simply run the Salt Virt migrate routine:
salt-run virt.migrate centos <new hypervisor>
Although not enabled by default, Salt Virt can also set up VNC consoles allowing
for remote visual consoles to be opened up. When creating a new VM using
virt.init, pass the
enable_vnc=True parameter to have a console
configured for the new VM.
The information from a
virt.query routine will display the VNC console port
for the specific VMs:
centos CPU: 2 Memory: 524288 State: running Graphics: vnc - hyper6:5900 Disk - vda: Size: 2.0G File: /srv/salt-images/ubuntu2/system.qcow2 File Format: qcow2 Nic - ac:de:48:98:08:77: Source: br0 Type: bridge
The line Graphics: vnc - hyper6:5900 holds the key. First the port named, in this case 5900, will need to be available in the hypervisor's firewall. Once the port is open, then the console can be easily opened via vncviewer:
By default there is no VNC security set up on these ports, which suggests that keeping them firewalled and mandating that SSH tunnels be used to access these VNC interfaces. Keep in mind that activity on a VNC interface that is accessed can be viewed by any other user that accesses that same VNC interface, and any other user logging in can also operate with the logged in user on the virtual machine.
Now with Salt Virt running, new hypervisors can be seamlessly added just by running the above states on new bare metal machines, and these machines will be instantly available to Salt Virt.