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Secure live migration with QEMU-native TLS

Context

The encryption offered by nova's :oslo.configlibvirt.live_migration_tunnelled does not secure all the different migration streams of a nova instance, namely: guest RAM, device state, and disks (via NBD) when using non-shared storage. Further, the "tunnelling via libvirtd" has inherent limitations: (a) it cannot handle live migration of disks in a non-shared storage setup (a.k.a. "block migration"); and (b) has a huge performance overhead and latency, because it burns more CPU and memory bandwidth due to increased number of data copies on both source and destination hosts.

To solve this existing limitation, QEMU and libvirt have gained (refer below <Prerequisites> for version details) support for "native TLS", i.e. TLS built into QEMU. This will secure all data transports, including disks that are not on shared storage, without incurring the limitations of the "tunnelled via libvirtd" transport.

To take advantage of the "native TLS" support in QEMU and libvirt, nova has introduced new configuration attribute :oslo.configlibvirt.live_migration_with_native_tls.

Prerequisites

Version requirement: This feature needs at least libvirt 4.4.0 and QEMU 2.11.
A pre-configured TLS environment—i.e. CA, server, and client certificates, their file permissions, et al—must be "correctly" configured (typically by an installer tool) on all relevant compute nodes. To simplify your PKI (Public Key Infrastructure) setup, use deployment tools that take care of handling all the certificate lifecycle management. For example, refer to the "TLS everywhere" guide from the TripleO project.
Password-less SSH setup for all relevant compute nodes.
On all relevant compute nodes, ensure the TLS-related config attributes in /etc/libvirt/qemu.conf are in place:
```
default_tls_x509_cert_dir = "/etc/pki/qemu"
default_tls_x509_verify = 1
```
If it is not already configured, modify /etc/sysconfig/libvirtd on both (ComputeNode1 & ComputeNode2) to listen for TCP/IP connections:
```
LIBVIRTD_ARGS="--listen"
```
Then, restart the libvirt daemon (also on both nodes):
```
$ systemctl restart libvirtd
```
Refer to the "Related information" section on a note about the other TLS-related configuration attributes in /etc/libvirt/qemu.conf.

Validating your TLS environment on compute nodes

Assuming you have two compute hosts (ComputeNode1, and ComputeNode2) run the virt-pki-validate tool (comes with the libvirt-client package on your Linux distribution) on both the nodes to ensure all the necessary PKI files are configured are configured:

[ComputeNode1]$ virt-pki-validate
Found /usr/bin/certtool
Found CA certificate /etc/pki/CA/cacert.pem for TLS Migration Test
Found client certificate /etc/pki/libvirt/clientcert.pem for ComputeNode1
Found client private key /etc/pki/libvirt/private/clientkey.pem
Found server certificate /etc/pki/libvirt/servercert.pem for ComputeNode1
Found server private key /etc/pki/libvirt/private/serverkey.pem
Make sure /etc/sysconfig/libvirtd is setup to listen to
TCP/IP connections and restart the libvirtd service

[ComputeNode2]$ virt-pki-validate
Found /usr/bin/certtool
Found CA certificate /etc/pki/CA/cacert.pem for TLS Migration Test
Found client certificate /etc/pki/libvirt/clientcert.pem for ComputeNode2
Found client private key /etc/pki/libvirt/private/clientkey.pem
Found server certificate /etc/pki/libvirt/servercert.pem for ComputeNode2
Found server private key /etc/pki/libvirt/private/serverkey.pem
Make sure /etc/sysconfig/libvirtd is setup to listen to
TCP/IP connections and restart the libvirtd service

IMPORTANT: Ensure that the permissions of certificate files and keys in /etc/pki/qemu/* directory on both source and destination compute nodes to be the following 0640 with root:qemu as the group/user. For example, on a Fedora-based system:

$ ls -lasrtZ /etc/pki/qemu
total 32
0 drwxr-xr-x. 10 root root system_u:object_r:cert_t:s0      110 Dec 10 10:39 ..
4 -rw-r-----.  1 root qemu unconfined_u:object_r:cert_t:s0 1464 Dec 10 11:08 ca-cert.pem
4 -rw-r-----.  1 root qemu unconfined_u:object_r:cert_t:s0 1558 Dec 10 11:08 server-cert.pem
4 -rw-r-----.  1 root qemu unconfined_u:object_r:cert_t:s0 1619 Dec 10 11:09 client-cert.pem
8 -rw-r-----.  1 root qemu unconfined_u:object_r:cert_t:s0 8180 Dec 10 11:09 client-key.pem
8 -rw-r-----.  1 root qemu unconfined_u:object_r:cert_t:s0 8177 Dec 11 05:35 server-key.pem
0 drwxr-xr-x.  2 root root unconfined_u:object_r:cert_t:s0  146 Dec 11 06:01 .

Performing the migration

On all relevant compute nodes, enable the :oslo.configlibvirt.live_migration_with_native_tls configuration attribute and set the :oslo.configlibvirt.live_migration_scheme configuration attribute to tls:
```
[libvirt]
live_migration_with_native_tls = true
live_migration_scheme = tls
```
Note

Setting both :oslo.configlibvirt.live_migration_with_native_tls and :oslo.configlibvirt.live_migration_tunnelled at the same time is invalid (and disallowed).

Note

Not setting :oslo.configlibvirt.live_migration_scheme to tls will result in libvirt using the unencrypted TCP connection without displaying any error or a warning in the logs.

And restart the nova-compute service:
```
$ systemctl restart openstack-nova-compute
```
Now that all TLS-related configuration is in place, migrate guests (with or without shared storage) from ComputeNode1 to ComputeNode2. Refer to the live-migration-usage document on details about live migration.

If you have the relevant libvirt and QEMU versions (mentioned in the "Prerequisites" section earlier), then using the :oslo.configlibvirt.live_migration_with_native_tls is strongly recommended over the more limited :oslo.configlibvirt.live_migration_tunnelled option, which is intended to be deprecated in future.
There are in total nine TLS-related config options in /etc/libvirt/qemu.conf:
```
default_tls_x509_cert_dir
default_tls_x509_verify
nbd_tls
nbd_tls_x509_cert_dir
migrate_tls_x509_cert_dir

vnc_tls_x509_cert_dir
spice_tls_x509_cert_dir
vxhs_tls_x509_cert_dir
chardev_tls_x509_cert_dir
```
If you set both default_tls_x509_cert_dir and default_tls_x509_verify parameters for all certificates, there is no need to specify any of the other *_tls* config options.

The intention (of libvirt) is that you can just use the default_tls_x509_* config attributes so that you don't need to set any other *_tls* parameters, _unless you need different certificates for some services. The rationale for that is that some services (e.g. migration / NBD) are only exposed to internal infrastructure; while some sevices (VNC, Spice) might be exposed publically, so might need different certificates. For OpenStack this does not matter, though, we will stick with the defaults.
If they are not already open, ensure you open up these TCP ports on your firewall: 16514 (where the authenticated and encrypted TCP/IP socket will be listening on) and 49152-49215 (for regular migration) on all relevant compute nodes. (Otherwise you get error: internal error: unable to execute QEMU command 'drive-mirror': Failed to connect socket: No route to host).

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